Biology, Politics

Medicine, the Inside View, and Historical Context

If you don’t live in Southern Ontario or don’t hang out in the skeptic blogosphere, you will probably have never heard the stories I’m going to tell today. There are two of, both about young Ontarian girls. One story has a happier ending than the other.

First is Makayla Sault. She died two years ago, from complications of acute lymphoblastic leukemia. She was 11. Had she completed a full course of chemotherapy, there is a 75% chance that she would be alive today.

She did not complete a full course of chemotherapy.

Instead, after 12-weeks of therapy, she and her parents decided to seek so-called “holistic” treatment at the Hippocrates Health Institute in Florida, as well as traditional indigenous treatments. . This decision killed her. With chemotherapy, she had a good chance of surviving. Without it…

There is no traditional wisdom that offers anything against cancer. There is no diet that can cure cancer. The Hippocrates Health Institute offers services like Vitamin C IV drips, InfraRed Oxygen, and Lymphatic Stimulation. None of these will stop cancer. Against cancer all we have are radiation, chemotherapy, and the surgeon’s knife. We have ingenuity, science, and the blinded trial.

Anyone who tells you otherwise is lying to you. If they are profiting from the treatments they offer, then they are profiting from death as surely as if they were selling tobacco or bombs.

Makayla’s parents were swindled. They paid $18,000 to the Hippocrates Health Institute for treatments that did nothing. There is no epithet I possess suitable to apply to someone who would scam the parents of a young girl with cancer (and by doing so, kill the young girl).

There was another girl (her name is under a publication ban; I only know her by her initials, J.J.) whose parents withdrew her from chemotherapy around the same time as Makayla. She too went to the Hippocrates Health Institute. But when she suffered a relapse of cancer, her parents appear to have fallen out with Hippocrates. They returned to Canada and sought chemotherapy alongside traditional Haudenosaunee medicine. This is the part of the story with a happy ending. The chemotherapy saved J.J.’s life.

When J.J. left chemotherapy, her doctors at McMaster Children’s Hospital [1] sued the Children’s Aid Society of Brant. They wanted the Children’s Aid Society to remove J.J. from her parents so that she could complete her course of treatment. I understand why J.J.’s doctors did this. They knew that without chemotherapy she would die. While merely telling the Children’s Aid Society this fact discharged their legal duty [2], it did not discharge their ethical duty. They sued because the Children’s Aid Society refused to act in what they saw as the best interest of a child; they sued because they found this unconscionable.

The judge denied their lawsuit. He ruled that indigenous Canadians have a charter right to receive traditional medical care if they wish it [3].

Makayla died because she left chemotherapy. J.J. could have died had she and her parents not reversed their decision. But I’m glad the judge didn’t order J.J. back into chemotherapy.

To explain why I’m glad, I first want to talk about the difference between the inside view and the outside view. The inside view is what you get when you search for evidence from your own circumstances and experiences and then apply that to estimate how you will fare on a problem you are facing. The outside view is when you dispassionately look at how people similar to you have fared dealing with similar problems and assume you will fare approximately the same.

Dr. Daniel Kahneman gives the example of a textbook he worked on. After completing two chapters in a year, the team extrapolated and decided it would take them two more years to finish. Daniel asked Seymour (another team member) how long it normally took to write a text book. Surprised, Seymour explained that it normally took seven to ten years all told and that approximately 40% of teams failed. This caused some dismay, but ultimately everyone (including Seymour) decided to preserver (probably believing that they’d be the exception). Eight years later, the textbook was finished. The outside view was dead on.

From the inside view, the doctors were entirely correct to try and demand that J.J. complete her treatment. They were fairly sure that her parents were making a lot of the medical decisions and they didn’t want J.J. to be doomed to die because her parents had fallen for a charlatan.

From an outside view, the doctors were treading on thin ice. If you look at past groups of doctors (or other authority figures), intervening with (they believe) all due benevolence to force health interventions on Indigenous Canadians, you see a chilling litany of abuses.

This puts us in a bind. Chemotherapy doesn’t cease to work because people in the past did terrible things. Just because we have an outside view that suggest dire consequences doesn’t mean science stops working. But our outside view really strongly suggests dire consequences. How could the standard medical treatment lead to worse outcomes?

Let’s brainstorm for a second:

  • J. could have died regardless of chemotherapy. Had there been a court order, this would have further shaken indigenous Canadian faith in the medical establishment.
  • A court order could have undermined the right of minors in Ontario to consent to their own medical care, with far reaching effects on trans youth or teenagers seeking abortions.
  • The Children’s Aid society could have botched the execution of the court order, leading to dramatic footage of a young screaming indigenous girl (with cancer!) being separated from her weeping family. Indigenous Canadians would have been reminded strongly of the Sixties Scoop.
  • There could have been a stand-off when Children’s Aid arrived to collect J.J.. Knowing Canada, this is the sort of thing that could have escalated into something truly ugly, with blockades and an armed standoff with the OPP or the military.

The outside view doesn’t suggest that chemotherapy won’t work. It simply suggests that any decision around forcing indigenous Canadians to receive health care they don’t want is ripe with opportunities for unintended consequences. J.J.’s doctors may have been acting out of a desire to save her life. But they were acting in a way that showed profound ignorance of Canada’s political context and past.

I think this is a weakness of the scientific and medical establishment. They get so caught up on what is true that they forget the context for the truth. We live in a country where we have access to many lifesaving medicines. We also live in a country where many of those medicines were tested on children that had been stolen from their parents and placed in residential schools – tested in ways that spit on the concept of informed consent.

When we are reminded of the crimes committed in the name of science and medicine, it is tempting to say “that wasn’t us; it was those who came before, we are innocent” – to skip to the end of the apologies and reparations and find ourselves forgiven. Tempting and so, so unfair to those who suffered (and still do suffer) because of the actions of some “beneficent” doctors and scientists. Instead of wishing to jump ahead, we should pause and reflect. What things have we done and advocated for that will bring shame on our fields in the future?

Yes, indigenous Canadians sometimes opt out of the formal medical system. So do white hippies. At least indigenous Canadians have a reason. If trips to the hospital occasionally for people that looked like me, I’d be a lot warier of them myself.

Scientists and doctors can’t always rely on the courts and on civil society to save us from ourselves. At some point, we have to start taking responsibility for our own actions. We might even have to stop sneering at post-modernism (something I’ve been guilty of in the past) long enough to take seriously its claim that we have to be careful about how knowledge is constructed.

In the end, the story of J.J., unlike that of Makayla, had a happy ending. Best of all, by ending the way it did, J.J.’s story should act as an example, for the medical system and indigenous Canadians both, on how to achieve good outcomes together.

In the story of Pandora’s Box, all of the pestilence and disease of the world sprung as demons from a cursed box and humanity was doomed to endure them ever more. Well we aren’t doomed forever; modern medicine has begun to put the demons back inside the box. It has accomplished this by following one deceptively simple rule: “do what works”. Now the challenge is to extend what works beyond just the treatments doctors choose. Increasingly important is how diseases are treated. When doctors respect their patients, respect their lived experiences, and respect the historical contexts that might cause patients to be fearful of treatments, they’ll have far more success doing what it is they do best: curing people.

It was an abrogation of duty to go to the courts instead of respectfully dealing with J.J.’s family. It was reckless and it could have put years of careful outreach by other doctors at risk. Sometimes there are things more important than one life. That’s why I’m glad the judge didn’t order J.J. back into chemo.


[1] I have a lot of fondness for McMaster, having had at least one surgery and many doctors’ appointments there. ^

[2] Doctors have a legal obligation to report any child abuse they see. Under subsection 37(2)e of the Child and Family Services Act (CFSA), this includes “the child requires medical treatment to cure, prevent or alleviate physical harm or suffering, and the child’s parent refuses to consent to treatment”. ^

[3] I’m not actually sure how relevant that is here – Brian Clement is no one’s idea of an expert in Indigenous medicine and it’s not clear that this ruling still sets any sort of precedent, given that the judge later amended his ruling to “make it clear that the interests of the child must be paramount” in cases like this. ^

Model, Physics, Science

Understanding Radiation via Antennas

It can be hard to grasp that radio waves, deadly radiation, and the light we can see are all the same thing. How can electromagnetic (EM) radiation – photons – sometimes penetrate walls and sometimes not? How can some forms of EM radiation be perfectly safe and others damage our DNA? How can radio waves travel so much further than gamma rays in air, but no further through concrete?

It all comes down to wavelength. But before we get into that, we should at least take a glance at what EM radiation really is.

Electromagnetic radiation takes the form of two orthogonal waves. In one direction, you have an oscillating magnetic field. In the other, an oscillating electric field. Both of these fields are orthogonal to the direction of travel.

These oscillations take a certain amount of time to complete, a time which is calculated by observing the peak value of one of the fields and then measuring how long it takes for the field to return to that value. Luckily, we only need to do this once, because the time an oscillation takes (called the period) will stay the same unless acted on by something external. You can invert the period to get the frequency – the number of times oscillations occur in a second. Frequency uses the unit Hertz, which are just inverted seconds. If something has the frequency 60Hz, it happens 60 times per seconds.

EM radiation has another nifty property: it always travels at the same speed, a speed commonly called “the speed of light” [1] (even when applied to EM radiation that isn’t light). When you know the speed of an oscillating wave and the amount of time it takes for the wave to oscillate, you can calculate the wavelength. Scientists like to do this because the wavelength gives us a lot of information about how radiation will interact with world. It is common practice to represent wavelength with the Greek letter Lambda (λ).

lambda class shuttle from star wars
Not that type of lambda. Image Credit: Marshal Banana on Flickr

Put in a more mathy way: if you have an event that occurs with frequency f to something travelling at velocity v, the event will have a spatial periodicity λ (our trusty wavelength) equal to v / f. For example, if you have a sound that oscillates 34Hz (this frequency is equivalent to the lowest C♯ on a standard piano) travelling at 340m/s (the speed of sound in air), it will have a wavelength of (340 m/s)/(34 s-1) = 10m. I’m using sound here so we can use reasonably sized numbers, but the results are equally applicable to light or other forms of EM radiation.

Wavelength and frequency are inversely related to each other. The higher the frequency of something, the smaller its wavelength. The longer the wavelength, the lower the frequency. I’m used to people describing EM radiation in terms of frequency when they’re talking about energy (the quicker something is vibrating, the more energy it has) and wavelength when talking about what it will interact with (the subject of the rest of this post).

With all that background out of the way, we can actually “look” at electromagnetic radiation and understand what we’re seeing.

animated gif showing oscillating magnetic and electric fields orthogonal to direction of travel
Here wavelength is labeled with “λ”, the electric field is red and labelled with “E” and the magnetic field is blue and labelled with “B”. “B” is the standard symbol for magnetic fields, for reasons I have never understood. Image Credit: Lookang on Wikimedia Commons.

Wavelength is very important. You know those big TV antennas houses used to have?

picture of house with old fashioned aerial antenna
Image Credit: B137 on Wikimedia Commons

Turns out that they’re about the same size as the wavelength of television signals. The antenna on a car? About the same size as the radio waves it picks up. Those big radio telescopes in the desert? Same size as the extrasolar radio waves they hope to pick up.

image of the VLA radio telescopes
Fun fact: these dishes together make up a very large radio telescope, unimaginatively called the “Very Large Array”. Image Credit: Hajor on Wikimedia Commons

Even things we don’t normally think of as antennas can act like them. The rod and cone cells in your eyes act as antennas for the light of this very blog post [2]. Chains of protein or water molecules act as antennas for microwave radiation, often with delicious results. The bases in your DNA act as antennas for UV light, often with disastrous results.

These are just a few examples, not an exhaustive list. For something to be able to interact with EM radiation, you just need an appropriately sized system of electrons (or electrical system; the two terms imply each other). You get this system of electrons more or less for free with metal. In a metal, all of the electrons are delocalized, making the whole length of a metal object one big electrical system. This is why the antennas in our phones or on our houses are made of metal. It isn’t just metal that can have this property though. Organic substances can have appropriately sized systems of delocalized electrons via double bonding [3].

EM radiation can’t really interact with things that aren’t the same size as its wavelength. Interaction with EM radiation takes the form of the electric or magnetic field of a photon altering the electric or magnetic field of the substance being interacted with. This happens much more readily when the fields are approximately similar sizes. When fields are the same size, you get an opportunity for resonance, which dramatically decreases the loss in the interaction. Losses for dissimilar sized electric fields are so high that you can assume (as a first approximation) that they don’t really interact.

In practical terms, this means that a long metal rod might heat up if exposed to a lot of radio waves (wavelengths for radio waves vary from 1mm to 100km; many are a few metres long due to the ease of making antennas in that size) because it has a single electrical system that is the right size to absorb energy from the radio waves. A similarly sized person will not heat up, because there is no single part of them that is a unified electrical system the same size as the radio waves.

Microwaves (wavelengths appropriately micron-sized) might heat up your food, but they won’t damage your DNA (nanometres in width). They’re much larger than individual DNA molecules. Microwaves are no more capable of interacting with your DNA than a giant would be of picking up a single grain of rice. Microwaves can hurt cells or tissues, but they’re incapable of hurting your DNA and leaving the rest of the cell intact. They’re just too big. Because of this, there is no cancer risk from microwave exposure (whatever paranoid hippies might say).

Gamma rays do present a cancer risk. They have a wavelength (about 10 picometres) that is similar in size to electrons. This means that they can be absorbed by the electrons in your DNA, which kick these electrons out of their homes, leading to chemical reactions that change your DNA and can ultimately lead to cancer.

Wavelength explains how gamma rays can penetrate concrete (they’re actually so small that they miss most of the mass of concrete and only occasionally hit electrons and stop) and how radio waves penetrate concrete (they’re so large that you need a large amount of concrete before they’re able to interact with it and be stopped [4]). Gamma rays are stopped by the air because air contains electrons (albeit sparsely) that they can hit and be stopped by. Radio waves are much too large for this to be a possibility.

When you’re worried about a certain type of EM radiation causing cancer, all you have to do is look at its wavelength. Any wavelength smaller than that of ultraviolet light (about 400nm) is small enough to interact with DNA in a meaningful way. Anything large is unable to really interact with DNA and is therefore safe.

Epistemic Status: Model. Looking at everything as antenna will help you understand why EM radiation interacts with the physical world the way it does, but there is a lot of hidden complexity here. For example, eyes are far from directly analogous to antennas in their mechanism of action, even if they are sized appropriately to be antennas for light. It’s also true that at the extreme ends of photon energy, interactions are based more on energy than on size. I’ve omitted this in order to write something that isn’t entirely caveats, but be aware that it occurs.


[1] You may have heard that the speed of light changes in different substances. Tables will tell you that the speed of light in water is only about ¾ of the speed of light in air or vacuum and that the speed of light in glass is even slower still. This isn’t technically true. The speed of light is (as far as we know) cosmically invariant – light travels the same speed everywhere in the galaxy. That said, the amount of time light takes to travel between two points can vary based on how many collisions and redirections it is likely to get into between two points. It’s the difference between how long it takes for a pinball to make its way across a pinball table when it hits nothing and how long it takes when it hits every single bumper and obstacle. ^

[2] This is a first approximation of what is going on. Eyes can be modelled as antennas for the right wavelength of EM radiation, but this ignores a whole lot of chemistry and biophysics. ^

[3] The smaller the wavelength, the easier it is to find an appropriately sized system of electrons. When your wavelength is the size of a double bond (0.133nm), you’ll be able to interact with anything that has a double bond. Even smaller wavelengths have even more options for interactions – a wavelength that is well sized for an electron will interact with anything that has an electron (approximately everything). ^

[4] This interaction is actually governed by quantum mechanical tunneling. Whenever a form of EM radiation “tries” to cross a barrier larger than its wavelength, it will be attenuated by the barrier. The equation that describes the probability distribution of a particle (the photons that make up EM radiation are both waves and particles, so we can use particle equations for them) is approximately  (I say approximately because I’ve simplified all the constants into a single term, k), which becomes  (here I’m using k1 to imply that the constant will be different), the equation for exponential decay, when the energy (to a first approximation, length) of the substance is higher than the energy (read size of wavelength) of the light.

This equation shows that there can be some probability – occasionally even a high probability – of the particle existing on the other side of a barrier.  All you need for a particle to traverse a barrier is an appropriately small barrier. ^

Falsifiable, Literature, Model, Science

Pump Six and the Perils of Speculative Fiction

I just finished Pump Six, a collection of short stories by Paolo Bacigalupi. A few weeks prior to this, I read Ted Chiang’s short story collection, Stories of Your Life and Others and I couldn’t help but be struck by the contrast between them. Ted Chiang writes stories about different ways the world could work. Paolo Bacigalupi writes stories about different ways the future could happen.

These are two very different sorts of speculation. The first requires extreme attention to detail in order to make the setting plausible, but once you clear that bar, you can get away with anything. Ted Chiang is clearly a master at this. I couldn’t find any inconsistencies to pick at in any of his stories.

When you try to predict the future – especially the near future – you don’t need to make up a world out of whole cloth. Here it’s best to start with plausible near future events and let those give your timeline a momentum, carrying you to where you want to go on a chain of reason. No link has to be perfect, but each link has to be plausible. If any of them leave your readers scratching their heads, then you’ve lost them.

Predicting the future is also vulnerable to the future happening. Predictions are rooted in their age and tend to tell us more about the context in which they were made than about the future.

I think Pump Six is a book where we can clearly see and examine both of these problems.

First, let’s talk about chains of events. The stories The Fluted Girl, The Calorie Man, The Tamarisk Hunter, and Yellow Card Man all hinge on events that probably seem plausible to Bacigalupi, but that feel deeply implausible to me.

The Fluted Girl imagines the revival of feudalism in America. Fiefs govern the inland mountains, while there is a democracy (presumably capitalist) on the coasts. This arrangement felt unstable and unrealistic to me.

Feudal societies tend to have much less economic growth than democracies (see part 2 of Scott’s anti-reactionary FAQ). Democracies also aren’t exactly great at staying calm about atrocities right on their doorsteps. These two facts combined make me wonder why the (Coloradan?) feudal society in The Fluted Girl hasn’t been smashed by its economically (and therefore, inevitably militarily) more powerful neighbours.

In The Tamarisk Hunter, the Colorado River is slowly being covered by a giant concrete straw, a project that has been going on for a while and requires massive amounts of resources. The goal is to protect the now diminished Colorado River from evaporation as it winds its way into a deeply drought-stricken California.

In the face of a bad enough drought, every bit counts. But there are much more cost effective ways to get your drinking water. The Colorado river today has an average discharge of 640m3/s. In a bad drought, this would be lower. Let’s say it’s at something like 200m3/s.

You could get that amount of water from building about 100 desalination plants, which would cost something like $100 billion today (using a recently built plant in California as a baseline). Bridges cost something like $3,000 per m2 (using this admittedly flawed report for guidance), so using bridges to estimate the cost, the “straw” would cost about $300 million per kilometer (using the average width of the Colorado river). Given the relative costs of the two options, it is cheaper to replace the whole river (assuming reduced flow from the drought) with desalination plants than it is to build even 330km (<200 miles) of straw.

A realistic response to a decades long California drought would involve paying farmers not to use water, initiating water conservation measures, and building desalination plants. It wouldn’t look like violent conflict over water rights up and down the whole Colorado River.

In The Calorie Man and Yellow Card Man, bioengineered plagues have ravaged the world and oil production has declined to the point where the main source of energy is once again the sun (via agriculture). Even assuming peak oil will happen (more on that in a minute), there will always be nuclear power. Nuclear power plants currently provide for only ten percent of the world’s energy needs, but there’s absolutely no good reason they couldn’t meet basically all of them (especially if combined with solar, hydro, wind, and if necessary, coal).

With improved uranium enrichment techniques and better energy storage technology, it’s plausible that sustainable energy sources could, if necessary, entirely displace oil, even in the transportation industry.

The only way to get from “we’re out of oil” to “I guess it’s back to agriculture as our main source of energy” is if you forget about (or don’t even consider) nuclear power.

This is why I think the stories in Pump Six tell me a lot more about Bacigalupi than about the future. I can tell that he cares deeply about the planet, is skeptical of modern capitalism, and fearful of the damage industrialization, fossil fuels, and global warming may yet bring.

But the story that drove home his message for me wasn’t any of the “ecotastrophes”, where humans are brought to the brink of destruction by our mistreatment of the planet. It was The People of Sand and Slag that made me stop and wonder. It asks us to consider what we’d lose if we poison the planet while adapting to the damage. Is it okay if beaches are left littered with oil and barbed wire if these no longer pose us any threat?

I wish more of the stories had been like that, instead of infected with the myopia that causes environmentalists to forget about the existence of nuclear power (when they aren’t attacking it) and critics of capitalism to assume that corporations will always do the evil thing, with no regard to the economics of the situation.

Disregard for economics and a changing world intersect when Bacigalupi talks about peak oil. Peak oil was in vogue among environmentalists in the 2000s as oil prices rose and rose, but it was never taken seriously by the oil industry. As per Wikipedia, peak oil (as talked about by environmentalists in the ’00s, not as originally formulated) ignored the effects of price on supply and demand, especially in regard to unconventional oil, like the bitumen in the Albertan Oil Sands.

Price is really important when it comes to supply. Allow me to quote from one of my favourite economics stories. It’s about a pair of Texan brothers who (maybe) tried to corner the global market for silver and in the process made silver so unaffordable that Tiffany’s ran an advertisement denouncing them in the third page of the New York Times. The problems the Texans ran into as silver prices rose are relevant here:

But as the high prices persisted, new silver began to come out of the woodwork.

“In the U.S., people rifled their dresser drawers and sofa cushions to find dimes and quarters with silver content and had them melted down,” says Pirrong, from the University of Houston. “Silver is a classic part of a bride’s trousseau in India, and when prices got high, women sold silver out of their trousseaus.”

Unfortunately for the Hunts, all this new supply had a predictable effect. Rather than close out their contracts, short sellers suddenly found it was easier to get their hands on new supplies of silver and deliver.

“The main factor that has caused corners to fail [throughout history] is that the manipulator has underestimated how much will be delivered to him if he succeeds [at] raising the price to artificial levels”

By the same token, many people underestimated the amount of oil that would come out of the woodwork if oil prices remained high – arguably artificially high, no thanks to OPEC – for a prolonged period. As an aside, it’s also likely that we underestimate the amount of unconventional water that could be found if prices ever seriously spiked, another argument against the world in The Tamarisk Hunter.

This isn’t to say that there won’t be a peak in oil production. The very real danger posed by global warming and the fruits of investments in alternative energy when oil prices were high will slowly wean us off of oil. This formulation of peak oil is much different than the other one. A steady decrease in demand for oil  will be hard on oil producing regions, but it won’t come as a sharp shock to the whole world economic order.

I don’t know how much of this could have been known in 2005, especially to anyone deeply embedded in the environmentalist movement. As an exoneration, that’s wonderful. But this is exactly my point from above. You can try and predict the future, but you can only predict from your flawed vantage point. In retrospect, it is often easier to triangulate the vantage point than to see the imagined future as plausible.

Another example: almost all science fiction before the late 00s drastically underestimated the current prevalence in mobile devices. In series that straddle the divide, you often see mobile devices mentioned much more in the latter books, as authors adjust their visions of the future to take into account what they now know in the present.

Writing is hard and the critic will always have an easier time than the author. I don’t mean to be so hard on Bacigalupi, I really did enjoy Pump Six and it’s caused me to do no end of thinking and discussing since I finished reading it. In this regard, it was an immensely successful book.

Epistemic Status: The math is Falsifiable, the rest is a Model.

Politics, Science

Special Topics in Nuclear Weapons: Laser Enrichment

In an effort to make my nuclear weapons post series a one stop resource for anyone interested in getting up to speed on nuclear weapons, I’ve decided to add supplementary materials filling any gaps that are pointed out to me. This supplementary post is on laser enrichment.

Enrichment is one of the more difficult steps in the building of certain nuclear weapons. Currently, enrichment is accomplished through banks of hundreds or thousands of centrifuges, feeding their products forward towards higher and higher enrichment percentages.

Significant centrifuge plants are relatively big (the Natanz plant in Iran covers 100,000m2, for example) and require a large and consistent supply of energy, which often makes it possible spot them in satellite imagery. The centrifuges themselves require a recognizable combination of components, which are carefully monitored. If a nation were to suddenly buy up components implicated in centrifuge design, it would clearly signal its intention to increase its enrichment capacity.

Recently, laser enrichment has emerged as an additional vector for proliferation. Properly called SILEX (separation of isotopes by laser excitation), this new technology has the potential to make enrichment (and therefore proliferation easier). This post discusses how laser enrichment works and puts the threat it represents in context. It’s both a summarization (and simplification) of the recent paper on laser enrichment in published in Science & Global Security by Ryan Snyder and the product of my extensive background reading on nuclear weapons.

How It Works

Like gas centrifugation, laser enrichment requires gaseous uranium hexafluoride (Hex). While the preparation of uranium hexafluoride doesn’t represent a significant technical challenge (compared to all of the rest of the work of building a nuclear weapon), it’s still the sort of work that most reasonable chemists try to avoid. “Requires work with a poisonous, corrosive, radioactive gas” will never be a selling feature of enrichment work.

Laser enrichment also requires a large laser capable of outputting 10.2µm light (which must be converted to 16µm using Raman scattering off of H2 gas), capable of pulsing 30,000 times per second. This appears to be just barely possible with current technology and impossible with off the shelf technology. It’s the sort of thing that would have to be custom assembled.

Also requiring custom assembly is the enrichment cell, which must have a nozzle capable of injecting a supersonic stream of uranium hexafluoride in such a way as to minimize post-injection expansion. The cell also must have an optically transparent window for your laser to shine through and must have several egress lines – peripheral ones for enriched product and a central one for the jet to flow out of.

Finally, if you want to make this maximally efficient, you’re going to need a mirror set up so as to have your laser pass through the gas twice. This corrects for the circular shape of the laser. Without this mirror, you won’t have enough coverage at that edges of the gas and you’re only going to operate at 78.5% of the maximum efficiency.

The whole setup looks like this:

Image Credit: A Proliferation Assessment of Third Generation Laser
Uranium Enrichment Technology

Once you’ve assembled all of this, you’re good to start enriching.

Remember, natural Hex is largely made up of 238UF6 and is only about 0.7% 235UF6. The purpose of enrichment is to increase the percentage of 235UF6 in the gas until it is almost entirely made up of this isotope of uranium.

The process SILEX uses to achieve this is relatively simple. You run the Hex and a carrier gas (the paper says SF6) through this system at supersonic speeds and low temperatures while pulsing the laser so as to hit the jet just as it leaves the nozzle. If you’ve tuned your wavelength as directed, then photons from the laser will kick any 235UF6 molecules they hit into a heightened vibrational state (called the v3 vibrational mode), while doing nothing to the 238UF6 molecules that make up most of the Hex.

235UF6 in the v3 vibrational mode will eventually revert to a lower energy (or “ground”) state, but it is unlikely to spontaneously revert to a ground state during the few milliseconds it takes to traverse the cell. For the purposes of SILEX, 235UF6 in the v3 vibrational mode will remain in that mode unless something acts on it to change it. To improperly anthropomorphize a particle for a second, this is “bad” for the excited 235UF6, because it “wants” to be at a lower ground state.

The excited 235UF6 could get external “help” from a collision with 238UF6 (this collision would allow it to release a photon and revert to its ground state), but this is unlikely if you keep the overall concentration of UF6 in the carrier gas low (the paper recommends 5%). This is in fact exactly what is done, because efficiency is maximized when 238UF6 doesn’t get a chance to collide with 235UF6.

When you put Hex in a carrier gas like SF6, you’re going to see the formation of transitory dimers. These are temporary, weak bonds between one Hex molecule and one SF6 molecule. These bonds are fairly stable, unless the Hex is in the v3 (or similar) vibrational mode. If dimer formation occurs between v3 235UF6 and SF6, the dimer is very short-lived. The excited 235UF6 dumps all of its extra energy into the dimer bond, resulting in a lot of recoil; both the 235UF6 and the SF6 go flying apart in opposite directions. It’s the dimer formation that causes a very different outcome from a simple collision with 238UF6.

This recoil tends to push 235UF6 to the edges of the stream. A skimmer positioned around the outlet collects this enriched product. Note that it won’t be entirely enriched; the outside edges of the jet will have plenty of 238UF6 because the jet is going to be mostly 238UF6 – or at least, it will be when natural or lightly enriched uranium is the input.

If you were doing this on an industrial scale, you’d set a bunch of these cells up in series, with the enriched product of each cell being the feed for the next. In this way, you’d get the same sort of cascade towards higher enrichment as you would with centrifuges.


Laser enrichment might be more space and energy efficient than centrifuge arrays.

I have to say might because there’s some uncertainty here. A few key parameters that determine ease of proliferation using SILEX are missing. This isn’t because of censors removing them for security reasons. It’s because this technology is so new that there are serious question marks hanging over it. SILEX has shown promise in lab scale experiments, but there doesn’t yet exist any proof that SILEX will be superior to centrifuge enrichment when it comes to enriching uranium on an industrial scale. Given that the pilot project has been stalled since GE pulled out, it may be quite a while before we know if SELIX will fulfill its promise or not.

It looks like a SILEX would allow a country with technology on the level of Iran to enrich the same amount of uranium with only 59% of the floor area. This would make enrichment a bit easier to hide, but would do nothing to stop leaks. It was human intelligence, not satellite photos that allowed the west to discover the work at Natanz.

The error bound on SILEX energy consumption is large enough that it’s unclear if there would be a power consumption benefit or cost for rogue states switching to SILEX from indigenous centrifuge technology. State of the art American centrifuges still beat SILEX on floor space and they may beat it in energy use.

Estimates for SILEX efficiency span an order of magnitude and in the upper two-thirds of that range it seems to be a clear winner (in terms of amount of energy required per percent enrichment). I couldn’t see any consensus on the relatively likelihood of high vs. low actual efficiency, but I would personally bet that a lot of the probability distribution exists near the bottom of the allowed efficiencies. I haven’t worked in nuclear science, but I have done chemistry, and my experience is that few processes perform as well on an industrial scale as you might expect from efficiency calculations done at laboratory scale.

Enrichment with SILEX is quite possibly easier than enrichment with centrifuges. That is to say, even if SILEX doesn’t allow rogue nations to enrich more efficiently, it might allow them to enrich at all. SILEX requires some advanced optics knowledge and the lasers needed aren’t exactly available off the shelf, but they are easier to design and build than specialized enrichment centrifuges.

Before centrifugation became the preferred method of isotope separation for nuclear weapons (and nuclear energy), gaseous diffusion was used. Gaseous diffusion plants use truly prodigious amounts of space and energy. There is absolutely no way that these things can be hidden or disguised as something else.

With the advent of centrifuges, proliferation became significantly easier. Countries used to be faced with no good path to a functioning bomb. Plutonium is relatively easy to acquire and separate, but it is very difficult to build a successful implosion weapon (and impossible to do so without alerting anyone with test detonations). Uranium was relatively difficult to enrich, which closed off the option of a simpler gun assembly weapon (it is impossible to build a gun assembly weapon using plutonium).

If you want a nuclear arsenal and don’t care that gun assembly weapons are wasteful and less useful for staging, then the advent of uranium enrichment via centrifugation was a boon to you. Gun assembly weapons don’t even necessarily require test detonations, which allows for the (slim) possibility of entirely clandestine nuclear arsenals – assuming enough uranium can be secretly enriched.

SILEX may eventually exacerbate this problem, to the point where any country with access to uranium could conceivably build a relatively low yield bomb (say a dozen or two kilotons).

At present, the technology is too new for this to be true. SILEX almost certainly has a few kinks left to be worked out. Trying to work them out at the same time as your country builds a new nuclear program isn’t ideal. Best to wait for India or Pakistan to figure them out and then leak them to you in exchange for favours or missile technology (this has been North Korea’s approach to nuclear weapons and it has worked quite well).

In a decade, SILEX may make proliferation even easier. I don’t think it will make it easy to the point where Al Qaeda or Daesh can attempt to build nuclear weapons (can you imagine Daesh setting up a high-energy laser laboratory in Raqqa?). But I do worry that countries like Saudi Arabia or the Philippines might see the calculus around proliferation change enough to justify their building of a small arsenal of uranium weapons.

That would be a disaster for world peace and stability.

Governments are already reacting to threat posed by SILEX by adding necessary components to export ban and international watch lists. If any nation buys up a bunch of laser components over a short time without a good explanation, the international community will now suspect enrichment. I’m sure there are many men and women in the basement of the Pentagon and CIA headquarters now watching all laser equipment sales for more subtle signals of gradual stockpiling. Don’t think for a second that SILEX somehow represents a cheat code for proliferation. It’s still untested and unproven and governments and international organizations are already taking steps to reduce the proliferation risk.

Most nuclear technology is dual use. Uranium enrichment by centrifugation has made proliferation easier. It also increased the energy return on investment from burning uranium in power plants from ~40x to over 1500x (see here if you want to double check my calculations). Because of centrifugation, nuclear power plants could permanently end our dependence on oil if coupled with new battery technologies (and upfront capital and political will to build them).

SILEX could further increase the energy return on investment, making nuclear power plants even more economical. But SILEX also has the potential to make proliferation easier. It’s still a new, experimental technology and it might not even pan out. Until we know for sure, it is certainly best for the world to proceed with caution.

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Nuclear Weapons: 8.0 High Value Anti-Nuclear Activism

Nuclear weapons represent an existential risk. I’ll let 80,000 Hours speak for me for a minute:

A survey of academics at the Global Catastrophic Risk Conference by Oxford University estimated a 1% chance of human extinction from nuclear wars over the 21st Century.

Luke Oman estimates the probability “for the global human population of zero resulting from the 150 Tg of black carbon scenario in our 2007 paper [delving into the effects of a single nuclear exchange] would be in the range of 1 in 10,000 to 1 in 100,000.” This being said, we think this estimate is too low, as it doesn’t account for the potential for weaknesses in their model or the risk of a societal collapse causing a permanent reduction in humanity’s ability to reach its potential (which is nonetheless an existential risk even if people remain).

If you’re interested in reducing the existential risk that nuclear weapons pose, I’ve identified a few areas where you may be able to make a difference.

8.1 Tactical Weapons

Countries have begun to reduce stockpiles of tactical weapons and put those that remain under better centralized control. No one ever wanted a fresh lieutenant in charge of the nuclear weapon that could eventually set off World War III – it just took everyone a while to realize this.

Still, it seems like this has primarily been possible because of the collapse of the Soviet Union. When the USSR seemed poised to overrun Europe, killing the commies was given priority over keeping humanity alive. Increasing regional tensions between Russia and NATO may result in a resurgence of tactical weapons.

Treaties that ban weapons under a certain yield, or require all nuclear warheads to have locks that can only be released by the civilian leadership of a country would be an excellent way to reduce the risk of conventional warfare leading to a nuclear exchange.

8.2 Arms Reduction Treaties

Not all arms reduction treaties are created equal. The Strategic Offensive Reductions Treaty (SORT) expired on the same day it came into full effect and set non-specific limits; while it may have reduced the total number of nuclear weapons deployed, it probably did this by causing the early retirement of already obsolescent systems. In addition, SORT had no verification provisions. We literally have no way of knowing if it actually had an effect.

On the other hand, the New Strategic Arms Reduction Treaty (New START) has a robust verification mechanism, including demonstrations that technology has been fully decommissioned and eighteen inspector visits each year. New START sets specific limits on ICBMs, SLBMs, nuclear armed bombers, and total deployed warheads. It will be in full force for at least three years, but might be extended longer. It comes up for review in 2019, so convincing the US and Russia to renew it will be very important.

8.3 Anti-ballistic missiles

The US ABM system represents a real threat to global peace. If it is demonstrated to be effective, we could see China rapidly increase its nuclear arsenal. If it’s expanded to the East Coast of the US, or Europe, we could see Russia do the same.

If you live in America, pressuring your congressional representative or senator to vote against any measures increasing funding for the ABM system could be very important. You can call it a waste of taxpayer money, demand it not be built in your backyard, etc.

If you live near one of the current ABM sites, or are near one of the sites for potential expansion, you can engage in direct action.

In addition to organizing protests (it should be easy to get people uneasy about nuclear weapons near them), you can attempt to bog down any expansion or new construction in and endless morass of red tape. If a system is being built near you, you should attend any community meeting you can, be as obstinate as possible, and jump on any zoning violation, rushed environmental assessment, or other bureaucratic mistake like a rabid pit bull. This won’t be very effective if new ABM sites are built entirely within existing military bases, but if even a single support strut has to go up for municipal approval, there’s potential to make an impact.

Current ABM sites are Fort Greely in Alaska and Vandenberg Air Force Base, California. Proposed eastern sites are SERE Remote Training Site in Maine, Fort Drum in New York, Camp Ravenna Joint Military Training Center in Ohio, and Fort Custer Training Center in Michigan.

8.4 Donations

Both 80,000 Hours and OpenPhil have done their own preliminary assessment of nuclear weapon risk.

Neither piece offers firm suggestions for the most effective charity and I lack the expertise to do my own evaluation. Both OpenPhil and 80,000 Hours suggest that there may not be much room for more funding, although OpenPhil suggests that effective anti-nuclear advocacy may be underfunded.

For what it’s worth, I’m donating to the Ploughshares Fund. They seem to have the correct focuses, from preserving the Iran deal, to removing tactical weapons from Europe, to opposing new ABM systems. I don’t think they have that much more room for funding, so I’d welcome a more thorough effectiveness evaluation that would allow people concerned with nuclear risk to confidently donate their money.

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Falsifiable, Politics, Science

Nuclear Weapons: 7.0 Strategy

Having covered the practicalities of nuclear physics, nuclear weapon design, and nuclear weapon effects, we may now turn our attention to the strategies that have grown out of these physical realities.

7.1 Tactical and Strategic Weapons

Broadly speaking, there are two kinds of nuclear weapons – tactical and strategic. This post has been focused primarily on strategic nuclear weapons, high yield weapons capable of destroying cities and hardened targets. Tactical nuclear weapons have smaller yields, allowing them to be hypothetically used on a battlefield that contains friendlies.

The line between the two gets somewhat blurred with the highest yield tactical weapons. Is a 5kt bomb tactical or strategic? No one really has a clear answer. These already crystal clear waters get muddied further when you add in “dial-a-yield” weapons, which can yield anywhere from <1kt to ~100kt. On the low end, they’re definitely tactical. But at the high end, they’re clearly strategic.

Most of the treaties that deal with nuclear weapons don’t cover tactical weapons. This is a bit of a problem, because tactical weapons are perhaps the easiest way that a conventional conflict could escalate into a nuclear conflict. It goes like this: my army is losing, so I have a fire-team use a tactical nuke launched from a recoilless rifle on your densest concertation of tanks. The 100t weapon totally destroys the formation, swinging the battle in my favour.

The nuke I used on you, the opposing general, is not a strategic weapon, so I don’t need codes from higher up or another person to agree with my decision.

You are now losing because those tanks occupied a key position. You reply with a 1kt tactical nuke of your own, fired from an 8″ howitzer 20km behind your own lines. It takes out 3,000 of my infantry. Satisfied, you go back to conventional war.

But I’m pissed off, so I dial up one of my short ranged tactical missiles to a 10kt yield. There’s a plume of smoke from the rocket launch, a bright flash, and a crater where your army used to be. I’m satisfied with a job well done, but your side is pretty enraged. So they call in a 50kt strategic nuke on an intermediate range ballistic missile that wipes out my forces and camp.

A few more levels of escalation and the ICBMs and SLBMs begin to fly. Once you believe nuclear war is inevitable, the only thing to do is try for a successful first strike and pray for the best.

7.2 First Strike, Second Strike, Counterforce, Countervalue

A first strike is an attempt to destroy an opponent’s nuclear arsenal before they can launch it at you. SLBMs or on station stealth bombers are the only real way to pull this off. The flight time for ICBMs between probable belligerents is much too long for the missiles to reach targets before those targets have a chance to respond.

Targets include airbases where nuclear bombers are known to be based, the known location of any mobile ICBMs, missile silos, docks where nuclear submarines may be resupplying, command and control systems, and key nuclear weapons decision makers. Separately, any nuclear submarines that have be detected will be attacked by the hunter-killer submarines shadowing them.

In all likely nuclear exchanges between larger nuclear powers (NATO/Russia, NATO/China, China/Russia, China/Pakistan, China/India, India/Pakistan, Pakistan/Israel and neglecting North Korea due to the primitive nature of its nuclear program), this won’t be enough. Some of the nuclear weapons will survive.

Baring a truly unlikely display of self-sacrifice and forgiveness, these remaining weapons will immediately be fired at the aggressor in a second strike – a retaliatory attack.

First strikes are predicted to be mostly counterforce, that is to say, aimed at an enemy’s military forces in general and their nuclear forces in particular. There will be civilian casualties, because there always are, especially with weapons as indiscriminate as nukes, but civilian casualties aren’t the goal of a first strike.

A second strike, on the other hand, would be primarily countervalue, that is to say, aimed at the most valuable targets an enemy possesses. Major cities, knowledge centres, and industrial centres are the primary targets in a countervalue strike. Civilian casualties are kind of the point and consequently will be rather high.

7.3 Mutually Assured Destruction

Nuclear policy has for decades been based on the idea of mutually assured destruction (MAD). Mutually assured destruction requires all nuclear armed powers to be committed to a massive countervalue retaliatory strike against any country which deploys nuclear weapons against them. Furthermore, this threat must be credible – enemy decision makers must believe it is real and can be carried out if necessary.

The goal of the mutually assured destruction doctrine is to prevent nuclear war by making it clear that all nuclear wars will be unwinnable, so that no power believes they can gain anything from them. Wargame succinctly summed up the desired end-state of the MAD doctrine with the famous line “the only winning move is not to play”.

For MAD to ensure stability, two things must be true:

  1. No actor can destroy the entire nuclear arsenal of another in a first strike.
  2. No actor can defend against a second strike well enough that they will escape unscathed.

While the current MAD equilibrium is relatively stable, it has come under threat from both the US and the USSR in the past. The closest we’ve come to nuclear self-annihilation has been those times when MAD had begun to break down.

The Cuban Missile Crisis was ultimately about first strike capability. The US had based ballistic missiles in Italy and Turkey that gave it the easy ability to target the USSR – and Soviet missiles (of which there were only 20 that could hit the continental United States from Soviet territory). With these forward deployed missiles and timely reconnaissance from the U2 spy plane, it had become perhaps possible for the US to wipe out the Soviet Union and face minimal retaliation.

When the Soviets began to build missile sites in Cuba, the problem became mutual. Suddenly each side had first strike capability. If you want to look for the hand of God in human affairs, I would suggest centring your search here. Conditions were riper for a first shot than a Mos Eisley cantina. It’s a genuine miracle that no one launched missiles.

The negotiated resolution to the Cuban Missile Crisis was publically all about Cuba. Kennedy promised to never invade again and Khrushchev promised to remove the missiles. But in secret, Kennedy promised to remove all of the US missiles based in Italy and Turkey. First strike capability was removed and equilibrium restored.

The second threat to MAD came from anti-ballistic missiles (ABMs). By the 1960s, both the US and USSR were working on ABM systems. The Soviets were building a network of ABMs around their capital Moscow, while the Americans were building a similar system around their missile silos in North Dakota.

These systems were imperfect and could be overwhelmed by MIRVs. But both sides were worried about the future; what if their enemy figured out perfect missile defense before they did? Both the US and USSR knew that If one side could gain a critical advantage in missile defense, they would be able to launch a first strike with impunity. The bitter irony was that systems designed to protect against nuclear attacks were making global nuclear war more likely.

This crisis was also defused through diplomacy. Both sides understood the risks and decided they weren’t worth it. The first Strategic Arms Limitation Treaty (SALT I) limited both the USSR and US to two ABM sites. Hot on the heels of this was the Anti-Ballistic Missile Treaty which revised the limit downwards to one site and limited the number of ABMs at each site to 100.

Unfortunately, the US unilaterally withdrew from this treaty in 2002 to begin work on a new missile defense system. If this system ever becomes operational to the point that the US can expect to survive a second strike from Russia or China, nuclear war will become imminent.

7.4 The Nuclear Triad

The delicate balance of MAD is maintained by the nuclear triad: ICBMs, SLMBs, and conventional bombers. Once a nation possesses all three legs of the triad it becomes almost impossible to remove their nuclear capability in a first strike.

Each leg of the triad has a purpose. ICBMs are static, but are relatively cheap and can often be launched quickly. SLBMs are more expensive and slightly harder to launch (they require accurate positioning for targeting) but are very hard to destroy. And conventional bombers have the greatest flexibility in avoiding attack, plus a very long range courtesy of in-air refueling.

These aren’t the only three methods that can round out a triad though. Really, the important thing is having three credible and disparate systems, such that it is impossible to remove your ability to make a countervalue second strike. Space based weapons (forbidden by treaties), air launched missiles, carrier based nuclear bombers, or nuclear torpedoes could all be used in place of one of the “standard” legs of the triad.

Only India, China, the United States, and Russia have confirmed nuclear triad capability. Israel is suspected of having a nuclear triad, but refuses to confirm or deny this assertion (Israel does wink suggestively when asked, which has led basically all experts to assume that they do in fact possess a nuclear triad).

7.5 Current Nuclear Strategy

Every country charts its own course on nuclear weapons. From public statements and acknowledged procurements, it’s possible to get some idea of each country’s strategy, but you have to understand that they really don’t broadcast these things. I mean, they broadcast them, but we shouldn’t take those statements at face value. There are a host of reasons – diplomatic, strategic, domestic, that prevent leaders from being entirely candid with their nuclear plans.

When reading into strategies, I focus on questions like: what are the known capabilities of deployed weapons? How many nuclear weapons can a country deploy? What delivery methods does a country possess? Where are its weapons based? What advances in technology are politicians highlighting in public speeches? Where have they faced technical difficulties? What countries are they friendly with? Unfriendly with?

I would also recommend avoiding the common pitfall of obsessing over the total number of warheads a country possesses. This number is much less important than the count of operational or deployed warheads. In any significant nuclear exchange, it is unlikely that any warheads but those immediately at hand for deployment will be used.

This section represents my best guesses at the current nuclear strategies of various countries. Please treat these as speculation, not as fact.

7.5.1 Russia

Russia wants to keep its status as a major nuclear power, but it needs to do it on a tighter budget than the USSR had. This means a focus on land based ICBMs, no truly stealthy fighters, and limited resources for its SLBM program.

Current sanctions on Russia have disrupted Russian supply chains and applied pressure on Putin to slash military spending – right as he becomes more confrontational with the rest of the world. Russia can’t afford to fall behind in the nuclear arms race. Its second strike capability is the only thing stopping the US from giving it much harsher ultimatums. Significant budget cuts would put this second strike capability under threat. But on the other hand, Russia can only afford its current military budget for so long.

This statement falsified if: real stealth bombers enter service with a sticker price of >$500,000,000 per unit, Russia manages a string of successful SLBM launches in 2017, the international sanction regime against Russia collapses with Trump as US president.

7.5.2 China

China’s nuclear arsenal is less advanced than that of Russia or the USA. MIRV-ready missiles have been rolled out only in the last decade and many of their missiles still lack MIRV capability (but they do incorporate some decoys and countermeasures). In addition, Chinese missiles are kept unfueled and without warheads in place, which drastically increases their second strike response time. They make up for this with a massive network of decoy silos, real silos, and tunnels built into the mountains of Central China. China only has a handful of nuclear missile submarines and its conventional bomber force is fairly obsolete.

China’s nuclear policy is explicitly second strike only. Based on all the facts above and what I know about China, I’m inclined to believe this. Historically, China has never cared much about what happens outside of China (broadly defined, of course). Since China already enjoys massive conventional supremacy over its neighbours, it has no need of nuclear weapons to intimidate them.

This statement falsified if: China renounces no first use, China threatens a non-nuclear state with nuclear attack, China has >10 active ballistic missile submarines by 2020, China develops a new dedicated heavy bomber.

7.5.3 India and Pakistan

Neither of these countries have sprung for forces really capable of mutually assured destruction and only India maintains a full nuclear triad. Instead of adopting MAD, they instead both aim to have forces just big enough to make a nuclear attack by the other not worth the risk.

Since these countries really only need to be able to deter each other (and possibly China), they’re freed from the need to spend to keep up with the US or Russia. Both India and Pakistan lack the ability to launch a truly significant countervalue strike in response to a first strike from the US or Russia. Given how unlikely the US or Russia launching a first strike on India or Pakistan is, this is a sensible approach.

This statement falsified if: Either of these countries test Mt range thermonuclear weapons, either of these countries develops an ICBM capable of targeting the continental United States (range >11,000km), either of these countries increases nuclear funding by >200%.

7.5.4 UK and France

These countries keep nuclear weapons because they’re members of the UN Security Council and it comes with the territory. Neither has a particularly robust nuclear force (the UK only has American made Trident SLBMs, France has indigenous SLBMs and nuclear capable bombers). It’s largely a prestige thing though. Neither country has been particularly enthusiastic about the nuclear rigmarole (and its price tag) since the end of the Cold War.

Nuclear policy in the UK and France is closely tied to the nuclear policy of NATO, although both countries do maintain some ability to conduct nuclear war on their own terms. Neither country has ruled out using nuclear against non-nuclear states in response to attacks with conventional forces and France has specifically mentioned that they would be willing to use nuclear weapons against countries that sponsor terrorism against them.

All this being said, it is unlikely that France or the UK would be the ones to start a global nuclear war.

This statement falsified if: Either the UK or France increases their supply of operational warheads, either the UK or France develops a full nuclear triad.

7.5.5 North Korea

North Korea’s nuclear weapons program is especially difficult to assess. In addition to the normal challenges when trying to understand a classified program, there’s the bluster of Kim Jong-un to sort through. Up until recently, experts thought ICBM technology was beyond North Korea. They were thought to be struggling with the re-entry heat shield, struggling with miniaturization, struggling with the whole endeavour.

Now, people are less sure. Has North Korea gained full ICBM capability? Or is this more bluster and staged photographs? There’s probably a dozen men and women in the Pentagon (and in many other places) who would love to know the answer for sure. My personal guess, based on the evidence (and the bluster) is that North Korea has a missile design that in theory could target the US, but they’ll need a year or three to get it working reliably. I don’t think they’ll pull off a successful test this year, but I won’t be surprised if they pull one off in 2018 or 2019. That also seems to be the view of the Ploughshares Fund, an anti-proliferation non-profit.

Even if North Korea can’t attack the US, there’s still Russia, China, Japan and South Korea at risk from its shorter range missiles. This represents a considerable threat to a large number of people. It’s tempting to laugh off these threats in light of the inflated numbers that North Korea likes to give for the yields of their weapons (e.g. claiming a 6kt detonation was a hydrogen bomb that could wipe out the whole US). You could look at the disconnect as evidence of a fizzle, but personally I see it as evidence that North Korea likes to exaggerate. In September, they tested a bomb with a yield of 10-20kt. Fizzle or not, if delivered to Seoul, it would kill over 100,000 people.

Under Kim Jong-il, the prevailing belief was that the nuclear program was a bargaining chip in order to get free food or other concessions from other countries. Its purpose under Kim Jong-un is less clear. Despite punishing sanctions, Jong-un has maintained and expanded the nuclear weapon and missile programs started by his father. Whether he is willing to trade them in for concessions or wishes to use them in an attempt at unification is unknown.

This statement falsified if: North Korea successfully tests a true ICBM (range >5,500km) with successfully atmospheric re-entry by the end of 2017 and analysts believe it has enough additional payload for a miniaturized bomb.

7.5.6 Israel

Israel’s nuclear weapons remain unacknowledged, because Israel has pledged to not be the country that “introduces” nuclear weapons to the Middle East. Israel’s statement should be given all of the skepticism one would give to Bill Clinton using the word “is”. Israel may intend “introduce” to mean “acknowledge” or “deploy”, but we’re all pretty sure they don’t intend “introduce” to mean what it literally does.

Israel wants to have nuclear weapons as the ultimate hedge against military aggression by its neighbours. In addition, it wants to ensure that none of its neighbours possess them. Given the clear support for genocide that some of its neighbours have expressed, this position is understandable. If it appears likely that one of its regional foes will develop nuclear weapons, Israel is likely to launch a conventional attack to stop their development. If a conventional attack fails, a nuclear one is not out of the question.

Many sources talk about how Israel holds nuclear weapons as a “Samson option” and is prepared to use them to utterly annihilate an enemy if it looks like they are in a position to destroy Israel. This is actually how I’d expect most countries to behave, so I think the obsession with the Samson Option in Western reports on Israel’s nuclear program has more to do with the story it makes than a real difference between, say, France and Israel.

Israel probably possesses a full nuclear triad. Since it does not confirm or deny its nuclear program, there are no publically available official details that would allow us to be sure of this. It does make sense though. Israel has the technical know-how to pull off the tricky parts of a triad, like SLBMs.

In the future, we can expect Israel to continue to hold onto its arsenal and continue to neither confirm nor deny its existence. I don’t think Israel is a particularly likely candidate to touch off a nuclear war, as it is unlikely to use nuclear weapons against another nuclear armed state. That said, Israeli use of nuclear weapons would almost assuredly result in many civilian casualties and is still an eventuality that basically everyone would like to avoid.

This statement falsified if: Israel joins the NPT and allows inspectors into its nuclear facilities, Israel publically acknowledges its nuclear arsenal, Israel does not launch an airstrike against any nuclear program started by another Middle Eastern country.

7.5.7 Iran

Iran does not possess nuclear weapons, but as recently as 14 years ago was probably working on them. Most analysts believe that this work mostly stopped with the US invasion of Iraq. Iran had no particular desire to become (more of) an international pariah for developing nuclear weapons, but couldn’t accept the risk of Iraq developing them without an Iranian counter. Iran remembered the nerve agent attacks that Iraq unleashed (with the assistance of the US) during the Iran-Iraq war and felt that any developments in Iraqi weapons of mass destruction had to matched.

Iran has been prevented from coming clean about its past development of nuclear weapons by the belief (rightly or wrongly) than any admission will result in sanctions or attempts at regime change from Western actors.

Iran does have a well-developed civilian nuclear program. Despite the wailing and gnashing of teeth among hawks, the current nuclear deal should prevent any breakout towards nuclear weapons. The deal includes a robust enforcement and inspection regime that has most global powers convinced that Iran won’t be able to restart nuclear weapons work secretly.

Donald Trump’s talk of reversing this deal is just that: talk. It isn’t a bilateral deal between Iran and the USA, it’s a multilateral deal between Iran, the Permanent members of the UN Security Council, and Germany. The US could unilaterally re-impose sanctions, but there would be a significant diplomatic cost for basically no gain; it took a network of international sanctions to bring Iran to the negotiating table the first time around, so it is doubtful that US sanctions alone would change anything. The Iranian economy isn’t very integrated with the US economy, further diminishing the sting of any unilateral sanctions. Honestly, the US would probably suffer just as much from a fresh round of sanctions as Iran would.

This statement falsified if: Iran renounces the nuclear deal, Iran leaves the NPT, Iran refuses to allow inspectors access to a site they wish to visit, inspections turn up clear evidence of nuclear weapons development done since 2005.

7.5.8 The United States of America

When Vladimir Putin goes to his magic mirror and asks “mirror, mirror on the wall, who’s the greatest nuclear power of all?”, the answer is invariably “the United States”. In every nuclear metric that matters (so, discounting the total number of warheads), the United States reigns supreme. It has the best stealth bombers, the most accurate missiles, and the biggest fleet of nuclear submarines. As the world’s one remaining superpower, the United States is the only country that is able to mount even a half-way decent first strike – although it probably can’t launch a successful first strike against any triad state.

I don’t know what US nuclear policy will look like going forward. If Donald Trump maintains good relations with Putin, then a nuclear exchange with Russia will be (even more) unlikely. I do think a nuclear exchange with China has become slightly more likely as a result of Donald Trump’s election, but I hope the risk is relatively low.

No matter how you cut it, the risk of a nuclear exchange is – and always has been – low. But no one truly knows how low “low” is. Is it 10% over the Trump presidency? 1%? Whatever it is, I wish it was lower.

I also wish Trump was less of a loose cannon. I can’t really make predictions about America’s nuclear policy over the next few years because the information I have is too heavily weighted towards hyperbole and bluster.

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Nuclear Weapons: 6.0 Delivery Mechanisms

All the nukes in the world are useless unless you have a way to get them to their targets. Aside from outlandish and potentially suicidal methods like suitcase nukes or nuclear artillery, there are three main ways of doing this: bombers, intercontinental ballistic missiles (ICBMs), and submarine launched ballistic missiles (SLBMs).

6.1 Bombers

The only nuclear weapons ever used in anger were delivered by B-29 bombers, the Enola Gay and the Bockscar. Because the Allies had attained near total air-superiority over Japan at the time of the bombings, it was possible for these bombers to go in without any real escort. They were accompanied only by weather reconnaissance and observation planes.

In a modern nuclear exchange, total air superiority would probably be required for a country to be able to openly deliver a bomb. If a nuclear bombing is attempted with anything less than total superiority, the attacker can expect to have all remaining anti-air defenses thrown at them.

Absent total air superiority, the only reasonable way to deliver a nuclear weapon via bomber is stealth. Conventional bombers can make a play at this by flying below radar, but this is very risky and doesn’t guarantee success. In states of heightened alert, the bomber would have to avoid both radar and settlements where residents might alert the target to the coming attack.

Stealth aircraft can make a better go at delivering bombs, especially when the target is on high alert. All new combat aircraft are billed as having some stealth capabilities, but the only true stealth bomber is the US B-2 Spirit. Its virtually invisible to most means of detection (it shows up about as well on radar as a large bird or a sphere a foot in diameter would) and can carry 18 tonnes of bombs 11,000km (this gives it a range of about 5,000km, neglecting in-air refueling).

The main disadvantage of bombers then, is the difficulty that they all (except the B-2) face in arriving at their target both intact and at the correct altitude to drop a bomb. There are a couple of significant advantages to bombers though.

They’re controlled by people. Really well-trained, smart people who know what they’re doing. Tell a pilot that it’s up to her to prevent a retaliatory strike on her home country and she’s going to be very motivated to carry out her mission. Maybe she’ll come up with a new trick and make it to her target. If she doesn’t, maybe one of her squadron mates will. Send in a dozen bombers and you force your enemy into a problem of resource allocation. They may end up spread too thin to stop them all. And if just one gets through…

Having pilots also makes bombers fairly accurate. The steep fall-off in weapon intensity with distance from the target (as discussed earlier in §5.1) demands a fair amount of accuracy and pilots can be significantly more accurate than some ICBMs.

Bombers are also the delivery method that’s hardest to stop at the source. During periods of heightened alert, countries will always keep nuclear armed bombers in the air. Any sign of a nuclear attack and they’ll be released for bombing runs on their prearranged targets. Unlike ICBs, there is no silo you can take out to stop them.

Additional Reading: B-2 Spirit, Nuclear Bomber, Stealth Aircraft

6.2 ICBMs

Intercontinental ballistic missiles are missiles capable of delivering nuclear warheads at least 5,500km from their launch site. Intercontinental ballistic missiles are distinguished from cruise missiles by their use of rocket engines and their suborbital trajectories. They leave the atmosphere during their boost phase and come back down on top of their target, using a guidance system and fins for limited maneuvering and final targeting once back inside the Earth’s atmosphere.

US and Russian ICBMs use multiple independent targetable re-entry vehicles (MIRVs). A single ICBM can carry many MIRVs, which allow it to simultaneously strike several targets. MIRVs were invented in response to anti-ballistic missiles, nuclear tipped missiles that detonate near incoming enemy missiles, causing them to fizzle or frying their electronics. The advent of MIRVs made missile defense mostly pointless, because it is much easier to build bigger ICBMs with more MIRV capability than it is to expand missile defense systems to deal with more incoming MIRVs.

MIRVs were one of the main factors pushing down bomb yields. The scaling factors we went over earlier mean that smaller weapons do damage much more efficiently than larger ones. It was MIRVs that made the delivery of these smaller weapons economical. Without MIRVs, launching 8 smaller warheads would require launching 8 smaller missiles, which would end up much more expensive than launching one really huge missile. With a MIRV, you get the best of both worlds – one missile, many warheads.

Improvements in US and Russian missile accuracy over the last 50 years have also driven the decrease in the warhead yields commonly fielded by those countries. Early ICBMs were accurate to within about half a kilometer, which necessitated big warheads if you wanted to be sure of annihilating your target (this is especially important when the target is hardened, like your enemy’s nuclear arsenal is liable to be). Modern US and Russian missiles are now accurate to something like 200m, which (using cubic scaling to approximate destruction) allows for the same change of destroying the target with about 1/15 the yield.

China lags behind on ICBM technology, with Chinese missiles only accurate to within 800m of their target. This results in China using much larger warheads (4-5 Mt) on its ICBMs than the 475kt US MIRV capable W88 or the 200-300kt warheads the Russians favour. It is counter-intuitive yet true that routinely using larger warheads is the sign of a less capable nuclear power.

ICBMs are stored on mobile launching units, or in missile silos away from large cities and built into mountains or underground. Both strategies are designed to protect missiles from enemy attack. Keeping ICBMs mobile makes them very hard to target with other missiles – where they are when the missile is launched may not be where they are when it arrives. Add this to the problem of finding the damn things in the first place and you have relatively good protection.

Missile silos were most useful when missile accuracy was much worse than it currently is. Missile silos are supposed to be impervious to everything but a direct hit from another nuclear weapon. Once a difficult task, this is now fairly possible. If nothing else, missile silos are useful because they will divert some enemy attacks away from populated areas. Still, the expense and relative uselessness of nuclear silos mean that no one is clamouring to build more of them. The Russians are pivoting towards mobile ground based launchers, while the USA is focusing its efforts on SLBMs.

ICBMs have several advantages over bombers. Missiles can endure g-forces, altitudes, and heat that would kill humans many times over. Taken together, this lets missiles launch with very rapid acceleration, travel at very high speeds, and use very efficient trajectories; basically they arrive on target much more quickly than a bomber can. They’re also much harder to intercept. Modern ICBMs come with a variety of countermeasures, from dummy MIRVs, to aluminum balloons, all of which make countering them extremely difficult.

The Iron Dome suggests that >90% missile interception might be technically possible, but intercepting ICBMs remains much more difficult than intercepting short range rockets, so don’t expect much progress anytime soon.

One disadvantage of ICBMS are their highly visible launches and re-entries. A successful stealth bombing provides no warning at all and a successful SLBM attack might provide only 2-10 minutes of warning. ICBMs take something like 30 minutes to cover intercontinental distances (say, Russia to the USA, or China to the USA). During this time targets can be evacuated and retaliatory strikes prepared.

Additional Reading: ICBM, MIRV, Minuteman III, Dongfen 5, RS-26, United States National Missile Defense

 6.3 Submarine Launched Ballistic Missiles

At one point, it made sense to have a firm distinction between SLBMs (which had fairly small ranges) and ICBMs. For modern weapon systems, the ranges are effectively the same. Gone are the days where submarines had to sneak right up to the coast to attack their targets. If you were to look at a globe centred on a modern US or Russian ballistic missile submarine, you’d see all the targets it can hit.

Modern nuclear armed submarines are also very stealthy. As long as they remain submerged they cannot be found by satellites. SONAR and thermal imaging remain about the only things that can find them. Active sonar will smoke a sub out pretty quick – at the cost of letting the submarine know it’s been found and giving away the position of the intercepting vessel. Passive SONAR can occasionally find them, but the ocean is big and nuclear submarine captains know a whole bunch of tricks for masking their SONAR signature.

Thermal imaging can find nuclear powered submarines by the wake of warm water they leave behind (warmed after cooling their nuclear reactors), but savvy captains (and all of them are) can minimize their changes of detection by cruising along boundaries between zones of different temperatures. These zones are so irresistible to subs that a French and British submarine managed to collide as they both (probably) followed one. This was obviously pretty embarrassing to both countries, but should stand as a testament to how damn stealthy these things are. Had either captain realized what was going on, he would have changed course.

Submarines powered by nuclear reactors can run for decades without any refueling. The only practical limit on how long a nuclear sub can stay submerged is the food supply. Water is collected from the ocean and air is recycled much as it would be on the ISS.

SLBMs have all the advantages of ICBMs, with the added advantage of stealth. The US has embraced them wholeheartedly. Its SLBMs are more accurate and more heavily MIRVed than its land based missiles; the Ohio class nuclear submarine carries 24 Trident II SLBMs with up to 8 W88 475kt warheads, each with an effective range of 11,000km and an average error less than 90m. The Russians, Chinese, and others have been less enthusiastic with their nuclear subs. Russia in particular has been having a lot of trouble getting new SLBM systems into active use.

This highlights the one real disadvantage of SLMBs. They’re expensive and technologically complicated. Just getting a missile to successfully launch from beneath the ocean is challenging enough. Add in stealth requirements and a nuclear reactor and it’s no wonder that the sea floor is littered with sunken nuclear submarines, primarily of Soviet origin (one unlucky Soviet nuclear sub actually sunk twice).

You could reduce the technical complexity by using a more traditional diesel-electric submarine, but you’d sacrifice much of the submarine’s endurance and ability to stay submerged. Batteries can only power a submarine for a few days (or hours, if it’s moving as fast as it possibly can) and diesel engines will quickly suffocate the crew if run underwater. Add to this the limited amount of diesel any sub can carry and nuclear submarines become the only real way to do long duration submerged deterrence patrols.

Additional Reading: Nuclear subs collide in Atlantic, Submarine launched ballistic missile, Ohio Class Submarine, Trident II, Borey Class Submarine, List of sunken nuclear submarines, Nuclear submarine accidents, Bulava missile troubles

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Falsifiable, Politics, Science

Nuclear Weapons: 5.0 Effects

To understand the effects of nuclear weapons, you first need to understand how those effects scale with weapon yield.

5.1 Scaling

Modern bombs are much smaller than the Tsar Bomba. The standard US nuclear warhead, the W88, is a “mere” 475kt, a yield that is 100x less than that of the Tsar Bomba. On the other hand, the W88 weighs in at 360kg, 75x lighter.

This may seem like a poor trade, but it’s actually a very good one, due to the fundamental properties of explosive scaling. Scaling factors are very important to weapons. They determine the stable equilibriums that designs fall into. For example: we have tanks instead of mechs because strength scaling and mass scaling together make tall vehicles very vulnerable to weapons.

Scaling factors for all nuclear weapon effects (the fireball, the shock wave, and electromagnetic radiation) are different, but we can use the scaling factor of electromagnetic radiation as an example.

A nuclear weapon emits a set amount of energy as photons – gamma rays and X-rays, as well as IR, UV, and visible light. These photons radiate out approximately equally in all directions. The energy that the photons carry is fixed, but the area that the energy covers isn’t. We call the amount of energy per square meter “intensity”.

Intensity is incredibly important. It’s what drives the differences in climate between Mercury (surface temperature: 427ºC) and Pluto (surface temperature: -218ºC). In nuclear weapons, the intensity of radiated photons determines if buildings are set afire from the heat or people die of radiation sickness.

Since energy is constant, intensity will depend only on the area the energy is spread out over. Luckily, it’s pretty easy for us to calculate this area as a function of distance from the bomb. Dividing the total energy by the surface area of a sphere of a certain radius, we get the following equation for intensity:

Where E0 is the initial energy of the bomb and d is the distance from the epicentre of the explosion.

Ten meters out from a 10kt (in the SI unit, joules, this is 41.8 TJ) bomb, the energy per square metre 33,300 MJ. Ten times further away, the energy per square metre is 333 MJ, a 100-fold decrease.

To get the desired destructive power, a certain intensity is necessary. An intensity of 372kJ per square meter is necessary to give third degree burns, for example. Ignoring loss from the air, you get this effect from a 10kt bomb out to about 3km. Increase the bomb size 100-fold to 1Mt, and the radius expands only ten-fold, to 29.9km.

These examples illustrate one of the fundamental scaling factors of nuclear weapons. The photon effect radius of a nuclear weapon is proportional to – at best – the square root of the power of the weapon. This means that there are intense diminishing returns to increasing the power of a weapon. Increase its power 25 times and the radius of destruction becomes five times bigger. Increase the power 50 times and the radius only increases sevenfold.

Blast radius and fireball size scale differently than radiation, but in all cases the scaling is square root or worse. In fact, you’ll soon see that radiation scales better than nearly every other destructive effect.

Taking into account this scaling factor, the W88 is (by one measure) 10x less destructive than the Tsar Bomba, but 75x lighter – a trade-off that makes much more sense. Keep this relationship in mind whenever nuclear weapons are described in terms of “the power of the atomic bomb that destroyed Hiroshima”. The policy implications of this relationship will also become clear later. For now, it’s important that you simply understand that relative destructive power and yield don’t correspond 1:1.

Additional Reading: Inverse Square Law

5.2 Direct Effects

Thus far, we’ve restricted our discussion of nuclear weapon detonation to the technical. There’s a cascade of neutrons and a bunch of energy is released as a by-product – that much is clear. But what does all that energy do? How do we get from neutrons to levelled cities and mushroom clouds?

There isn’t as much clear, well-curated information on this topic as I’d like, but perhaps that’s only to be expected. As near as I can tell, here’s what happens:

  1. A lot of heat (and some photons and neutrons) get generated by fission or fusion
    1. The fission of an atom releases a huge amount of energy. Only 7% of this in the form of fission neutrons and gamma rays; most is in the kinetic energy of the atom fragments, which will be travelling at about 4% of the speed of light.
    2. Fusion reactions output mainly high energy neutrons. These are captured by the dense tamper around the fusion core, allowing them to cause fission, or to impart their kinetic energy to another atom. Most fusion neutrons that don’t collide with the tamper will escape.
  2. About one microsecond after detonation, the core and tamper of a bomb will be a cloud of plasma a couple metres in diameter, with temperatures exceeding 10,000,000ºC.
  3. Via blackbody radiation, the plasma emits x-rays. These x-rays heat the surrounding air to a similar temperature.
  4. The very air becomes incandescent, releasing a bright pulse of light.
    1. Depending on yield, distance, and atmospheric conditions the pulse can be permanently or temporarily blinding for anyone who looks at it.
    2. As well as visible light, IR and UV light is emitted. The combined radiance of all of this light can set buildings on fire or give people severe burns.
  5. The superheated air in the very centre of the explosion pushes against the surrounding air, acting like a giant piston and producing a massive shock front.
  6. Compression in the shock front causes it to briefly become a dense plasma, temporarily blocking the light from the incandescent air closer to the core.
  7. The compressed air of the shock front begins to expand rapidly, dropping in temperature and becoming clear. The fireball in the centre can once again be seen.
  8. This shock wave travels at approximately the speed of sound. Whenever it hits something (a house, a vehicle, a tree), it causes damage via two mechanisms.
    1. Static overpressure: the direct hammer-blow of all that dense air striking at once.
    2. Dynamic overpressure: the drag associated with the wind of the shock-front’s passage, which can tear, tumble and drag objects.
  9. Back in the centre of the blast, there’s still a bunch of hot air. It will quickly cool to the point where it no longer glows, but it will still be much brighter than the surroundings.
  10. This hot air begins to rise, pulling up debris from the ground (at this point, there will be plenty) into the vacuum its rising creates. The hot air also expands and the outside edges cool, which causes rotating internal air currents that help to draw in more air from below. This forms the characteristic mushroom cloud of a nuclear explosion.
  11. Between the vacuum caused by the rising mushroom cloud and the vacuum caused by the initial shockwave, a steady wind will blow back towards ground zero until equilibrium is reached. This wind will further toss around debris and can help to fan the flames of any fires that have started.

[Image Credit: Wikipedia/Mushroom Cloud]

 5.2.1 Fireball

The nearby detonation of an atomic bomb is utterly devastating to infrastructure. Everything within the central fireball will be annihilated. The size of the fireball varies: 150m for a 10kt blast (slightly smaller than Hiroshima), 720m for the modern 475kt W-88 favoured by America, and 4.62km for the monstrous 50Mt Tsar Bomba. Ideally, fireball effects would scale as the square root of the yield. In actuality, they scale a bit worse than this, as the fifth root of the square of the radius (i.e. the 2.5th root). I’m not sure exactly what causes this, possibly some weird property of plasma, or just general fluid dynamics oddness.

[Data Source: Nukemap 2.42] Trend line has equation .

5.2.2 Shockwave

As deadly as the fireball is, most of the damage from a nuclear explosion comes from the shockwave. Weapon designers carefully model the shockwave and use these insights to come up with an optimal detonation height for various effects – like levelling reinforced buildings or destroying residential areas. Models take into account the “Mach stem”, the angle at which some of the wave will be reflected off the ground and constructively interfere with the rest of it, leading to increased destruction.

To get an idea of the damage a shockwave causes, we can look at the radius within which the maximum pressure increase is 20 psi and the radius within which the maximum pressure increase is 5 psi. 5 psi is the blast pressure required to level residential buildings, while 20psi will demolish even heavy concrete buildings.

Unlike radiation effects, blast pressure increases with cube root of the yield. This scaling – like the shockwave itself – is driven by heat. The pressure air exerts is directly proportional to its temperature (this relationship is linear and given by the ideal gas law: PV = nRT). To get a 5 psi overpressure at a certain radius, the bomb must ultimately heat all the air within the radius to a temperature that will cause a 5 psi increase in pressure. The energy taken to heat a material is proportional to the mass of material to be heated. The mass of air is proportional to its volume. And volume of a sphere is really easy to calculate: . Chaining all these observations together, we’re left with radius increasing as the cube root of explosive power.

This means that for every 1000-fold increase in bomb power, you’ll see a 10-fold increase in destructive radius. In terms of overpressure effects, the W88 is about 4.7 times less destructive than the Tsar Bomba, while being 75 times lighter. This trade-off comes up even better than for radiation.

[Data Source: Nukemap 2.42] 5 psi trend line has equation , 20 psi trend line has equation .

5.2.3 Direct Radiation

Nuclear weapons produce two types of damaging radiation (they’re both photons, just at different energy levels): thermal and ionizing. Ionization radiation (mainly gamma rays) is responsible for causing acute radiation poisoning and later cancers. Thermal radiation (light, from IR to UV) is responsible for the horrendous burns nuclear weapons survivors often bear.

In a vacuum, both of these would exhibit scaling with the square root of the yield, as discussed earlier. In real world conditions though, there’s another key factor in play: the atmosphere. Air is actually fairly good at absorbing gamma radiation. For every 150m that a group of gamma rays travels through the air at sea level, about half of them are absorbed. This is cold comfort if you ever find yourself at ground zero of a nuclear explosion, but it means anyone more than a few kilometres away has fairly little to fear from direct radiation. Once atmospheric absorption is taken into account, the radius where gamma radiation is lethal increases with approximately the 6th root of the yield. This means that even very large bombs scarcely irradiate more people than their smaller counterparts.

As blasts become larger, fewer and fewer people are affected by direct radiation. The radius of complete destruction (20 psi overpressure) is smaller on 10kt bombs than the radius at which radiation fatalities are common. But the differences in scaling means that by the time a bomb is 575kt the radii are equal. Beyond this size, the radius of complete destruction will be larger than the radius of radiation effects and most casualties will come from the shockwave, not radiation.

IR, visible, and UV light are much less affected by the atmosphere. If the atmosphere absorbed light at the same rate it absorbs gamma rays, the sun would appear 717 billion billion times brighter on an airplane at cruising altitude as it does at sea level. This obviously isn’t the case – the sun is approximately as bright in both cases. This difference in absorption means that the radius at which nuclear weapons cause burns scales with close to the square root of the yield (the small amount of energy absorbed by the air does mean that it scales slightly slower in atmosphere than in vacuum).

[Data Source: Nukemap 2.42] 50% Deaths trend line has equation , 3rd Degree burns trend line has equation .

Additional Reading: Effects of Nuclear Explosions, Nuclear Weapon Design: Fission, Nuclear Weapon Design: Fusion, Mushroom Cloud, Nukemap and The Nuclear Double Flash.

5.3 Indirect Effects

Part of the horror of nuclear weapons comes from fallout, the lingering radiation left behind after a nuclear detonation. Fallout doesn’t last forever (and remember, the more unstable and radioactive an element is, the quicker it breaks down into something stable), but while it is around it can sicken and kill. Fallout can also cause illness and death far from the site of the initial blast, increasing the human toll of any nuclear weapon detonation.

Fallout is composed of unstable, radioactive isotopes that are scattered after a nuclear bomb is detonated. Fallout is mainly comprised of fission by-products (some of these are stable, but many are themselves radioactive and must conduct additional decay before they become stable) and left over fuel (remember, fission efficiency is almost never higher than 40%, leaving 60% of the fuel weight in radioactive waste). Depending on bomb detonation height, there may also be neutron activated fallout. Neutron activated fallout arises when stable elements are bombarded with neutrons and either capture the neutron, or fission from the energy of the collision. Since nuclear weapons tend to be detonated high in the air (with the hope of maximizing the shock wave), neutron activated fallout is a small portion of the total fallout. Either way, all fallout behaves similarly.

Some of the fallout will be blown up into the stratosphere by the force of the blast, or carried up in the wake of the rapidly rising fireball. These fallout products end up distributed fairly evenly across the whole globe. Nuclear testing before the partial and complete test bans resulted in a dramatic rise in strontium-90 and caesium-137 levels in humans all over the globe. These isotopes can cause cancer and other problems if ingested in significant amounts and the threat posed by steadily increasing global levels was enough to prompt the test ban treaties.

Stratospheric fallout is the minority; most of the fallout remains in the area of the blast. It’s still dispersed in the atmosphere, but its subject to local winds, not the global jet stream. The largest particles begin to fall immediately. Not all of them will be radioactive – some of the falling matter will be simple vaporized dirt or water – but it will never be safe to assume that any particles falling in the wake of a nuclear explosion are benign.

A high altitude burst doesn’t guarantee that the particles that rain down will be fallout free. Even if no neutron activation occurs, some of the material that rains down will be contaminated with radioisotopes produced by the blast. After the Castle Bravo nuclear test, coral contaminated with radioisotopes fell like snow over a large area, causing severe radiation burns whenever it touched human skin.

In the first day after a bomb is detonated, half of the local fallout will be deposited – unless it rains, in which case even more will fall. Rain is actually quite likely after a nuclear weapon detonation because fine particles dispersed in the atmosphere (like the dirt drawn up in a mushroom cloud) can help start the process of raindrop formation. Rain makes decontamination even harder, as the radioactive ions that travel down with raindrops tend to bond to external surfaces, requiring sandblasting to remove them.

The danger of the fallout varies with local atmospheric conditions, the size of the bomb, the efficiency of the bomb, and where the bomb detonates. Winds can disperse fallout, affecting more people, but giving each person a lesser dose. Bombs with a high efficiency create less fallout than bombs with lower efficiency. Bombs that get more of their power from fusion will generally have less fallout than a bomb of the same yield that gets more energy from fission.

Because of the potential variance in conditions, there are few general rules about fallout. I’ve seen something called the “Seven Ten” rule bandied about. The rule claims that every sevenfold increase in time after the detonation leads to a tenfold decrease in radiation from fallout. So after seven hours there will be ten times less radiation compared to the first hour and after forty-nine hours (approximately 2 days) there will be one hundred times less radiation.

I spent a lot of time confused by this. Remember half-lives from earlier? Instead of a fixed ratio of times (i.e. seven times) producing a fractional drop in radioactivity (i.e. ten times), I thought there should be fixed period of time that produces a fractional drop in radioactivity. If there really is a tenfold drop in radiation after seven hours, then it means that the half-life of the isotopes in the fallout would average out to 2.1 hours. Which should predict there would be a one-hundred hold decrease in fallout after fourteen hours (The equation is  which gives approximately 1/100). This definitely isn’t the case, which was the cause of my confusion.

I think the 7-10 rule is correct because of the mixture of isotopes we see in fallout. The most common isotopes in fallout (and their half-lives are): neptunium-240 (61.9 minutes), neptunium-239 (2.1 days), uranium-237 (6.75 days), iodine-131 (8 days), tritium (12 years), caesium-134 (20 years), strontium-90 (28.8 years), caesium-137 (30 years), technetium-99 (211,000 years), and zirconium-93 (over 1,000,000 years). The widely disparate half-lives lead to a variety of zones, each of which is dominated by a different half-life.

The 7-10 rule is an approximation that more or less fits the wonky data that results from this mixture. But it isn’t a very good approximation – it’s accurate to within 25% for the first two weeks and accurate within 50% for the first six months. After that, fallout is dominated by isotopes with similar half-lives and fits an exponential decay model, rendering the 7-10 rule basically useless.

Iodine-131 is one of the most famous fallout products and is primarily dangerous if consumed. Once in the body, it will be concentrated in the thyroid, where it can cause immediate damage or eventual cancer. This effect can be minimized with iodine tablets, which essentially “fill-up” the thyroid with safe iodine, leaving no room for iodine-131. Recommended dosage of iodine varies with the severity of the radioactive contamination and isn’t recommended for anyone over 40 except in cases where they may face acute thyroid damage. It’s also recommended to avoid drinking milk if you suspect any contamination with iodine-131.

Neptunium-239 and uranium-237 are responsible for most of the gamma radiation in fallout in the early days after a nuclear blast (neptunium-240 dominates for a few hours, but promptly fades). This is actually fairly good. After 20 days, there will be 1000-fold less radiation from neptunium-239 as there was immediately preceding the blast. Uranium-237 is a bit longer lived, requiring about 67 days for a 1000-fold decrease in radioactivity. Whether this represents a safe level is dependent on the initial amount and the relative abundance of neptunium-239/uranium-237 and other elements.

If you know or suspect that your area has been exposed to fallout, minimize your time outdoors. Your dwelling will offer excellent protection against alpha and beta particles and some protection against gamma radiation. If you must venture outside, wear many layers of clothes to protect yourself from beta particles. Don’t drink water without filtering it first. Try to avoid food produced after the fallout started, especially milk. Food produced before the nuclear exchange should be safe, as long as the outside is washed with clean water. Peeling fruit will also suffice. You can relax these precautions as the weeks and months wear on. In the years after fallout occurs, be aware of your surroundings. Hot spots (with fatal levels of radiation) may exist for several years. If you see dead trees or animals with no signs of rot, head in the other direction quickly.

This is just the barest of outlines. There are many guides out there that will go into specifics. Unfortunately, many guides have an implicit agenda (either: “scare people into becoming anti-nuclear activists”, or “keep our population from panicking about nukes”). If you know of a good, scientifically accurate guide, please link it in the comments. As additional reading, I’ve provided the official US Government planning guide, which seems to be accurate. In addition, I’ve linked to a more technical overview of fallout production and decay (Residual Nuclear Radiation and Fallout).

Additional Reading: Iodine Prophylaxis, Nuclear Fallout, Planning Guidance for Response to a Nuclear Detonation, Residual Nuclear Radiation and Fallout

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Falsifiable, Politics, Science

Nuclear Weapons: 4.0 Weapon Design

The last section required that you take it on faith that nuclear weapons are hard to design. Now it’s time to get into the nitty-gritty details of weapon design and understand why that is.

Nuclear explosions require a critical mass of the right unstable isotope. But there’s no safe way to store an assembled critical mass. As soon as you get to the critical mass, the chain reaction starts and an explosion will occur without drastic countermeasures.

All nuclear weapon design ultimately starts with this problem of assembling a critical mass in situ (and only ever in situ).

The first atomic bombs used one of two methods: gun assembly or implosion. These methods are still used to this day in fission weapons or in the fission first stage of multiple stage weapons.

4.1 Gun Assembly Design

[Image Credit: Wikipedia/Nuclear Weapon]

The gun assembly method was used in Little Boy bomb dropped on Hiroshima. In this method, sub-critical hemispheres (or a ring and a cylinder) are combined by conventional explosives into a critical mass (inside a neutron reflective tamper, which further decreases the necessary fissile mass).

This method is highly inefficient and suffers from “fizzling”. Basically, the pieces tend to become supercritical before they fully touch. The massive energy released by this reaction will then blow the pieces far apart before the reaction can complete. Only 1% of the uranium in the Hiroshima bomb was used up in the explosion. The rest was scattered and eventually rained down as fallout.

The only possible fuel in gun-assembly bombs is U-235. Plutonium fissions much more quickly, leading to the sub-critical pieces being blown apart before any significant mass of the plutonium can fission.

Due to these problems, this method has mostly fallen out of use, except in applications where only one dimension can be large (such as artillery shells).

Additional Reading: Little Boy, Nuclear Artillery, Fizzle, and Gun-type assembly weapon

4.2 Implosion Design

implosion assembly design

[Image Credit: Wikipedia/Nuclear Weapon]

Implosion type weapons start with a sub-critical mass and use explosives to compress it until it becomes critical. As the density increases, fewer neutrons escape the mass without triggering further fission events, leading to criticality despite the lower than normally necessary mass. An outer shell directly around the core that reflects neutrons can further decrease the mass necessary for a detonation.

The fizzling problem that plagues the gun-type device is also present here – eventually, the nuclear chain reaction will overwhelm the force imparted by the conventional explosives and blow the fuel apart, stopping the fission progress. Tamper design plays a factor in this; due to its very strong and heavy uranium tamper, the Fat Man plutonium bomb held together for a few hundred additional nanoseconds, allowing it to attain 20% efficiency.

In addition to tampers, there are various strategies to mitigate the breakup, all adding cost or technical complexity. For example, some nuclear weapons add a layer of aluminum-beryllium alloy between the explosives and the tamper to slow down the explosive shock wave and cause the core to be held compressed for slightly longer. This tweak can marginally increase the efficiency of a weapon.

Additional Reading: Implosion-type weapon and Fat Man

4.3 Miniaturizing Weapons

The core of a nuclear weapon is very small and relatively light (compared to conventional munitions). Most of the size and weight of a nuclear weapon comes from the explosives, tamper, and superstructure necessary to hold it all in the right place. The Fat Man bomb was egg shaped, 3.3 metres long and 1.5m in diameter at its thickest. The whole thing weighed 4.67t. the plutonium core was only 6.4kg, 0.14% of the total weight.

There’s no point having a weapon you can’t deliver. Methods that worked to deliver bombs across the 2500km that separated US island airbases and Japan weren’t feasible when dealing with the vast expanse of the Pacific, or the 8500km between the missile silos in the central United States and Moscow. Mass is the principle limit – the lighter its payload, the further a missile or bomber might fly.

Making weapons more powerful and miniaturizing them are two sides of the same coin. Every innovation that makes a bomb blast bigger can also potentially allow a smaller weapon to have the same effect as a larger weapon.

There are many unique challenges to miniaturizing weapons, such as correctly focusing explosions to create the desired pressure pattern. Regardless of the specific features necessary for miniaturization, it’s important to understand why miniaturization is such a big deal. North Korea, for example, has only possibly succeeded in miniaturizing its weapons to the point that its missiles can carry them any significant range. Until it thoroughly conquers this technical hurdle, only its closest neighbours have anything to fear.

4.4 Boosted Weapons

Boosted weapons were the first atomic bombs to make use of both fusion and fission, although they still get almost all of their energy from fission. Boosted weapons are all of the implosion type. Instead of a solid core, a boosted weapon will use a core with a hollow centre. In this hollow will be an equal mixture of tritium and deuterium.

Detonation proceeds as normal in the implosion assembly method, but with one extra wrinkle. The intense heat and pressure of the plutonium explosion compresses the deuterium/tritium mix to the point where these atoms begin to fuse into helium. Deuterium has two neutrons and one proton; tritium has three neutrons and one proton. Helium most commonly has two of each. Which means that every single fusion event also releases a neutron and imparts into that neutron a great amount of kinetic energy – it will be moving. These neutrons are the goal of the fusion stage.

Recall that fission chain reactions occur because neutrons from each fission event create further fission events. Adding a bunch of bonus neutrons to the mix puts the whole process on steroids. It helps that fusion neutrons move even faster than fission neutrons, so when they cause fission to happen, even more neutrons are released.

Using a boosted weapon, efficiency can be doubled. Which means that the same mass can give twice the yield, or the same yield can be attained with half the mass (because of this, boosting is one of the principle mechanisms of miniaturization).

There are a host of other benefits to boosting. Because the efficiency is increased, a smaller, lighter tamper can be used (these days they’re made of beryllium, which reflects neutrons but is not nearly as dense as uranium). Because the tamper is lighter, less explosives are required to compress the whole package. Boosting also gives a higher efficiency, so there’s no need for an additional focusing layer of aluminum/beryllium, leading to further savings in direct mass and mass of explosives necessary to drive the implosion.

All of these, combined with the reduction in plutonium mass necessary to get the same yield means that bombs have shrunk dramatically since the earliest days of nuclear weapons. The Fat Man bomb was 4.67t and 3.3m by 1.5m. It had a yield of 20kt. The first boosted weapon, the US “Swan” had a weight of just 47.6kg and measured 58cm long by 29.5cm in diameter, with a yield of 15kt, there was only a small loss of power for a 100x decrease in mass.

While it’s possible to build bombs in the >100kt range using boosted fission, this is rarely done. Fission remains fairly inefficient, so the amount of fissile material and tritium that must be used to get these yields quickly becomes wasteful. Very high yields remain the sole providence of fusion bombs, which can achieve these yields much more cheaply (recall how difficult and expensive enrichment is – to put a dollar value on it, the US pays $5,000 per gram of weapons grade plutonium-239).

There’s only one real drawback to boosted weapons: tritium. Tritium has a half-life of just 12 years. Even worse, it breaks down into helium-3, a form of helium with a single neutron that really “wants” to have two neutrons instead. Because of this, helium-3 “poisons” nuclear weapons by capturing neutrons that would otherwise cause fission. This means that boosted weapons must be periodically serviced and the helium-3 removed and replaced with fresh tritium. This is expensive (tritium cost $30,000 per gram in 2003 but is probably much more expensive now; we can’t calculate the cumulative cost because no government is willing to share the amount of tritium that is in each of their nukes, but it’s probably large) and almost certainly tricky (again, I can’t be sure, because no one releases their refueling procedures).

Additional Reading: Swan, Tritium, and Boosted Fission Weapon

4.5 Alarm Clock/Sloika

The Alarm Clock (named because Teller thought it would “wake up” the United States to the possibilities present by fusion weapons) or Sloika (Russian for a type of layered cake dessert) is a single stage boosted fission weapon that gets up to 20% of its yield from fusion (compare the ~1-2% that boosted weapons get from fusion).

The Sloika is made up of three layers. In the centre is a classic fission core, like in the normal implosion detonation design. Surrounding this is lithium-6 deuteride. The outer layer is unenriched uranium-238.

When this whole contraption is detonated (and detonating it takes a lot of explosives due to the three layers), three reactions occur in sequence. First, the core goes critical and fissions, ejecting a bunch of neutrons. Second, these neutrons hit the lithium-6 deuteride, which first cause lithium-6 to fission into tritium, which promptly fuses with the deuterium in the intense heat. The fusion reaction releases a lot of heat energy, a lot of radiation, and a lot of very fast neutrons. Finally, these fast fusion neutrons hit the natural uranium and cause it to fission. Since fusion neutrons are about 14 times more energetic than fission neutrons, they can cause fission even in unenriched uranium-238. The neutrons the uranium-238 releases during fission actually lack the energy to cause a self-sustaining chain reaction within itself, but they are capable of converting lithium-6 into tritium and helping the tritium fuse with deuterium. For a brief moment, this bomb has a stable multi-step chain reaction (fusion à high energy neutrons à fission à lower energy neutrons à lithium converted to tritium à fusion). Then it tears itself apart.

The Sloika derives most of its explosive power from relatively cheap natural uranium, which makes it a more cost effect way of getting yields in the 100s of kilotons compared to pure or boosted fission. It’s also safer, because most of its yield comes from a fuel incapable of spontaneous fission. Despite this it can’t truly compete with fusion weapons for cost effectiveness and lacks the ability to scale to the Mt range (as the amount of explosives necessary to detonate it grows infeasibly large at higher yields).

Because of these inadequacies, the Sloika proved a dead end in weapon design and is not used in any current nuclear weapons.

Additional Reading: Joe 4 and Alarm Clock/Sloika

4.6 Teller-Ulam Design

The Teller-Ulam design is necessary to economically achieve multi-megaton yields with devices small enough to be delivered intercontinentally. Teller-Ulam weapons (also known as thermonuclear bombs or H-bombs) use multiple stages of fission and fusion and incorporate concepts previously seen in boosted, implosion, and Sloika weapons. Here’s what the design looks like:

[Image Credit: Wikipedia/Thermonuclear Weapon]

The primary is a standard boosted implosion bomb, normally with a yield in the range of 10-20kt. The secondary is made up of a “sparkplug” of highly enriched plutonium or uranium, a supply of lithium-6 deuteride (the fusion fuel), and a natural or depleted uranium tamper (made primarily of uranium-238). In many designs, the bomb is also packed tightly with a plastic foam.

Detonation begins with the primary, which works exactly like the boosted implosion design described above (while boosting isn’t strictly necessary, boosting is important for reducing the size of the weapon and so in practice will be used in almost all modern thermonuclear weapons). As the primary detonates, three separate forces begin to exert immense pressure on the secondary.

First is X-ray radiation. The primary produces x-rays (in addition to neutrons and gamma rays), which can be mirrored by the outer casing to focus on the secondary. These x-rays have momentum and therefore exert pressure when they collide with the secondary. The large amount of high energy x-rays exerts a pressure equivalent to tens of millions of atmospheres, beginning the process of compression.

Plasma from the foam also plays a role in compression. X-rays aren’t just hitting the secondary. They’re also being absorbed by the foam. No plastic can withstand such an intense barrage of x-rays – so it almost immediately converts into plasma. As this plasma tries to expand in the confines of the bomb, it exerts even more pressure on the secondary, probably an order of magnitude more than the x-ray radiation alone.

Finally, the x-rays cause the tamper to begin to vaporize. Gaseous uranium boils off the surface under the intense x-ray bombardment. For every action, there must be an equal and opposite reaction and such is the case here. The uranium boiling off the surface pushes the rest of the uranium into the fusion fuel and it pushes it hard. The ablation pressure in a thermonuclear weapon is an appreciable fraction of the pressure at the centre of the sun, equivalent to many billions of Earth atmospheres.

Which one of these ultimately causes the secondary to detonate is intensely classified. What we do know is that one (or more) of these eventually causes the fissile “sparkplug” to go supercritical, which pushes on the fusion fuel from another direction and provides neutrons to activate it. Shortly after the sparkplug ignites, fusion begins.

Fusion provides a bit less than half of the total power of the average thermonuclear bomb. The rest comes from the fission of the uranium tamper with the very fast neutrons produced in the fission process.

Total yield varies from a hundred kilotons to a dozen megatons. It’s actually possible to make one bomb design that can have multiple yields (called “dial-a-yield”), by varying the amount of tritium in the primary (and therefore the pressure under which the secondary is compressed).

The Teller-Ulam design has the same disadvantage as boosted weapons: constant maintenance is required to replace the unstable tritium necessary to boost the first phase. This disadvantage pales beside the massive power of this design. It’s the only economical (in terms of cost, weight and size) way to achieve yields in the megaton range.

While a two-stage design is by far the most common, there is no theoretical cap on the number of stages this weapon can have. Each stage provides the compressive force to ignite the next. In this manner, yields up to a gigaton of TNT can be achieved, although a bomb this large would be very difficult to deliver, even with the general efficiencies of this design. The largest bomb ever detonated, the Soviet Tsar Bomba used three stages, massed 27t, and had a total yield of 50 Mt (although it used lead tampers to minimize fallout; had the tampers been uranium the yield would have been 100Mt – and fallout from the fission would have irradiated large swathes of the USSR).

Additional Reading: Thermonuclear Weapon, History of the Teller-Ulam Design, and Tsar Bomba

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Falsifiable, Politics, Science

Nuclear Weapons: 3.0 Proliferation

There are currently nine countries with acknowledged or suspected nuclear arsenals. Five of them are signatories of the Non-Proliferation Treaty (NPT), the main international treaty aimed at minimizing the number of nuclear armed states. Ideally, no country or group would have nuclear weapons. Unfortunately, we don’t live in an ideal world; the NPT is maybe the next best thing.

The NPT acknowledges the right of the permeant UN Security Council members (UK, USA, France, China, and Russia) to possess nuclear weapons even as it bans anyone else from getting (or trying to get) them. The remainder of the nuclear armed states (Israel, Pakistan, India, and North Korea) haven’t signed on to NPT or signed and later withdrew from it. South Sudan also isn’t a signatory of the NPT – I think they just haven’t gotten around to it – but no one is particularly worried about that (for reasons that will soon become apparent).

In the nuclear sense, proliferation – the thing this treaty is trying to prevent – is the spread of nuclear secrets, nuclear capability, or nuclear weapons to state or non-state actors that do not already possess them. Proliferation is fairly universally regarded as a bad thing. Luckily, attaining nuclear weapons is very difficult.

Earlier, I talked about how much information is classified. Interestingly, it tends to be only the specifics of nuclear weapons that are classified. Schematics and detailed procedures are under lock and key, but general principles are all over the internet. The next section of this post series covers historical and modern nuclear weapon design. This is totally legal. There’s no law in Canada or the US against disseminating any of this information (really mom and dad, I promise, this is okay).

There are a couple reasons for this laissez-faire attitude.

First, the general design of nuclear weapons is fairly easy for any competent physicist to derive from first principles, once they know what they’re looking for. The Teller-Ulam design was probably re-created 2-4 times by separate groups of physicists. Some of these re-creations used only basic knowledge of what byproducts the bomb produced and its approximate yield. Since computers will only get more powerful and physicists will only understand physics better, it stands to reason that this feat is becoming easier and easier to repeat. In any given university physics department, there are probably physicists who’ve guessed at the parts of the Teller-Ulam device that are still classified.

Second, this doesn’t really matter. Nuclear weapons are incredibly hard to actually build. Understanding in abstract how something works doesn’t mean you can go out and build it. Think about cars; even though you might understand the principles behind an internal combustion engine in the abstract, you’re probably incapable of building one. I know I certainly couldn’t. I don’t have the right materials. Even if I had them, I don’t have a blueprint to go by. And even if I were to come up with a design and assemble it, I’d most likely end up creating an underpowered and unreliable engine, not up to the standards of Ford, let alone Ferrari.

This maps well to the problems a state or non-state actor would face if they tried to build a nuclear weapon. First, they’d have difficulty acquiring materials. Then they’ve have more serious difficult coming up with a blueprint that makes good use of those materials. If they persevere and successfully create nuclear weapons, they’ll at first only have weak weapons, not up to the standards of the rest of the world.

In terms of materials, all nuclear weapons require inherently unstable isotopes – otherwise there would be no neutrons with which chain reactions could occur. These unstable isotopes (mainly plutonium-239 and uranium-235) are rare (or in the case of plutonium-239, basically non-existent) in nature. The half-lives of these isotopes see to that. Pu-239’s half-life is many orders of magnitude less than the age of the world. All of the Pu-239 the Earth original had is long since decayed. U-235 is longer lived than Pu-239 (it’s half-life is about 1/5 the age of the Earth), but it’s still rare; uranium deposits are mostly of the more stable (and therefore useless) isotopes.

Any moron can cause a nuclear detonation if given a critical mass of pure plutonium-239 (for the record, this is 12kg). Luckily (and despite what Doc Brown thought about the future), it is almost impossible for anyone (let alone morons) to get their hands on any amount of pure Pu-239. Furthermore, there is a huge gap between setting off an explosion in your lab and building a weapons system that can reliably deliver a nuclear payload to a hostile target.

For the actors that wish to try this, there are two paths to a bomb. The first requires uranium, the second, plutonium.

3.1 Uranium

There are a few advantages of using uranium in a nuclear weapons program. You don’t require research reactors just to get fuel for your bombs and the actual bomb design is much simpler. That said (and fortunately for the world), it is much more difficult to enrich uranium than it is to enrich plutonium.

Enriching the uranium – separating out different isotopes so that you’re left with only the most unstable ones – is a massive technological undertaking. First you have to mine it or import it. Either way every other country with a functioning intelligence service is going to find out about it and take note. But that’s just the first and easiest step.

Once you have your uranium ore, you have to dissolve it in nitric acid. Then you add ammonia. Then hydrogen gas. Then you mix it with hydrofluoric acid (which is incredibly nasty to work with). Then you fluoridate it some more with fluorine gas (this is even worse; it’s poisonous and it turns into hydrofluoric acid in your lungs if you happen to breath it in). This laborious and dangerous process gives you uranium hexafluoride, which is a real joy to work with (in the same way that being on the beach in the middle of a category 5 hurricane is a relaxing tropical vacation). Uranium Hexafluoride (hex for short) is incredibly toxic, explodes on contact with water, and corrodes most metals.

You’re going to need to find a metal it doesn’t corrode though (I recommend aluminum) because the next step is putting this terrible chemical into a giant centrifuge, adding some heat to turn it into a gas, and swinging it around as fast as you can. Since all of the isotopes have different masses, this will eventually create a distribution, with heavier isotopes (those with more neutrons) near the bottom. It’s the same principle as sand settling to the bottom of water in gravity, except that here gravity alone isn’t enough.

Even the immense force of the centrifuge really isn’t enough to get an appreciable amount of the necessary isotopes. You need to repeat the process with a thousand other centrifuges, all feeding forward, all enriching the uranium just a bit more, until you get a few kilograms of highly enriched uranium (you’ll have started with several dozen tons of uranium ore). The amount of energy, engineering, and time this takes is staggering.

Actually, this laborious and energy intensive process is the “easy” way of enriching uranium. Prior to the invention of centrifuge enrichment, a process known as gaseous diffusion was used. Compared to it, centrifuges require very little energy. This has been great for the energy return on investment of civilian nuclear plants, but less good for proliferation risk.

This process may eventually become even easier, due to technological advances like laser enrichment. But for now, you have to put in this work if you want uranium for your bomb.

Again, all of this is necessary for uranium bombs because naturally occurring uranium is depleted. To make nuclear weapons, you need highly unstable uranium. But all the uranium on earth was created billions of years ago, in the hearts of now long-dead stars. Over time, more and more of the unstable uranium has broken down, leaving mostly the more-stable isotopes.

2 billion years ago, fission could occur in uranium deposits. That’s now impossible.

When people discuss enriched uranium, they frequently talk about enrichment percentage. This is the relative mass of the fissile isotopes compared to the total mass of the material. For most power plants, an enrichment of 3-5% is used. For certain experimental reactors, including those that produce the radioisotopes necessary for medicine, 15-20% is more common. For nuclear weapons, the uranium must be enriched to about 80%, although higher enrichment is better. Low amounts of contaminants are necessary for nuclear weapons to function, whereas contaminants are well tolerated in nuclear reactors.

“Simple” enrichment of uranium to weapons grade costs untold millions of dollars. Of all the countries that do not currently possess nuclear weapons, only Iran, Germany, and Japan could enrich uranium up to weapons grade in a reasonable time frame. Non-governmental actors (like Al-Qaeda or Daesh) would find it essentially impossible to create their own fissile materials. The only way that they could gain access to the fuel for a nuclear weapon is if given it by another party.

3.2 Plutonium

It is much easier to acquire enough weapons-grade plutonium for a bomb than it is to acquire weapons-grade uranium. There are two reasons for this: separation is easier and the mass required to produce a plutonium bomb is lower than the mass required to produce a uranium bomb. Plutonium has a critical mass of 11kg, about five times less than that of uranium. This means that a viable plutonium bomb requires about one fifth the fissile material as a viable uranium bomb.

Weapons-grade plutonium starts with uranium. Like I said before, the plutonium-239 used in bombs no longer exists in nature.

To get plutonium from uranium, you need a nuclear reactor that’s running on uranium. This means that even when a country builds a bomb using plutonium, they must enrich some uranium. This presents all of the challenges outlined above, partially allayed by the fact that the enrichment percentage required is not very high, merely a few percent.

Inside any uranium fuelled nuclear reactor, some U-238 atoms will absorb neutrons, becoming U-239. This is a very unstable isotope (half-life: 23 minutes), which tends to briefly moonlight as Np-239 (half-life: ~2 days) before fulfilling its destiny and becoming Pu-239 (half-life: 24,110 years). Thus in many nuclear reactor designs, this Pu-239 will hang around in the fuel rods, occasionally decaying, fissioning, or absorbing neutrons (to form Pu-240), but largely just sitting there, waiting to be recovered.

If you want to get plutonium for a bomb, recover it you must. There are a variety of ways to do this, but all of them are much easier than centrifugation. The most common one is PUREX, which I’ll use as a representative example. In PUREX, you take the uranium fuel pellets from the reactor and dissolve them in very concentrated nitric acid, discarding anything that doesn’t dissolve. You then run a mixture of tributyl phosphate and kerosene over the acid. Any uranium and plutonium will move into the kerosene phase, while other fission products will remain in the acid. To separate the uranium from the plutonium, you run the kerosene mixture over water with ferrous sulphamate dissolved in it. The plutonium will react with the ferrous sulphamate, pick up a charge, and move into the water. The uranium will stay in the kerosene.

It’s easy to separate uranium from plutonium because they have a different number of protons. This means that they react differently with many chemicals. Extraction schemes take advantage of these different reactions to set up a scenario where the plutonium ends up in one solvent (like water in the PUREX example) and the uranium ends up in another (like kerosene). Complicated centrifuge arrangements are only necessary when dealing with different isotopes of the same element, where you can’t use tricks like this.

Weapons-grade plutonium (largely Pu-239) does have some problems with other plutonium isotopes. Remember how the critical mass for a plutonium bomb is much lower than that of a uranium bomb? This is possible because plutonium-239 is on a hair trigger where fission is concerned. This is doubly true for plutonium-240, in a way that is very problematic for weapons designers. Plutonium-240 is so prone to detonation that it often detonates early, blowing apart the bomb prematurely and leading to what’s termed a “fizzle” (this will be covered more in the next section; for now, you’ll just have to trust me that fizzles lead to uselessly weak bombs).

No one wants to separate Pu-239 from Pu-240; one of the major advantages of plutonium bombs are that you don’t needs to set up a huge centrifuge plant. To avoid having to separate the two isotopes, groups that are preparing plutonium for bombs aim to avoid the production of Pu-240 altogether. This means that any reactor optimized for producing plutonium can only run for about 90 days at a time. After uranium has been in a reactor for 90 days, the Pu-240 concentration is too high to easily build a working bomb. Despite this, the International Atomic Energy Agency runs audits on spent fuel from reactors, ensuring that no plutonium can be diverted from civilian reactors to weapons.

To economically start and stop a reactor every 90 days, you need a special reactor design. Civilian light-water nuclear reactors won’t do the trick. They have a huge pressure vessel that needs to be laboriously disassembled by specially trained divers every time they needs to get at the fuel. This is so inconvenient that civilian reactors are normally only cracked open once a year – by which point the plutonium has far too much Pu-240 to be viable in most weapons.

Reactors optimized for plutonium production allow for the rapid cycling of U-238 pellets through the reactor core. This requires quite a bit of engineering work – which has to be done from scratch unless you can find a country willing to share their schematics with you. It’s also basically impossible to hide the purpose of a reactor like this. Any IAEA inspector who sees your reactor will understand right away what you’re doing with it.

Once you have your reactor and your fuel, you have to decide how you want to run it. The shorter your cycles, the closer to your plutonium to pure Pu-239, but the more you’re going to pay per gram (in reagents, labour, wasted fuel rods, and wasted time as you cycle the reactor). The US uses >97% Pu-239 in the nuclear weapons on its submarines (Pu-240 produces a lot of gamma rays, which would be dangerous for the crews in close quarters), while its silo based weapons only use ~93% pure Pu-239.

To give an idea of the cost difference for increasing purities, the US Government helpfully lists 87% Pu-239 as $5,840 per gram, while 94% Pu-239 is $10,990 per gram. At these prices, the 3-4kg of plutonium in an atomic bomb would cost about $44 million if weapons-grade (and untold millions more if super-grade).

3.3 Next Steps

I asserted above that it is much more difficult to build a bomb out of plutonium than uranium. This is because the simplest type of nuclear weapon, the “gun” based design, does not work with plutonium. I’ll cover this in depth in the next post in the series. Here, I’m going to discuss problems common to all nuclear weapons designs because there’s significant overlap. Even with the simplest gun design, building a reliable, deliverable nuclear weapon is a significant engineering challenge. There’s no off the shelf design to copy, so you’re going to have to come up with your own solutions to problems like:

  • How can I get this to detonate every single time?
  • How can I make this package small enough that it is easy to deploy?
  • How can I ensure this thing detonates at the correct altitude?
  • How can I package this such that it doesn’t get messed up by wild swings in temperature and pressure?
  • How can I mount this on a missile?
  • How can I keep that missile from burning up on reentry? (This is one of the last things preventing North Korea from having a weapon system capable of targeting the USA)

Eventually, you’re going to have to test out your design. This means you’re going to have to set up specialized test chambers underground. You won’t want to detonate a bomb in the atmosphere because a) this is super-duper illegal under international law and b) It’s super-duper obvious to all of the UN Security council members (and any country with a functioning espionage program) that it was you who just test detonated a bomb. A combination of a) and b) means that atmospheric detonations are a one-way ticket to becoming an international pariah and all the sanctions that entails.

Underground tests are only slightly better. Seismometers will detect all but the smallest nuclear test detonations when they’re conducted underground, allowing several countries (most notably the US, with its excellent seismometer arrays) to detect and precisely locate the test detonation and estimate the yield. On the bright side, if you have the good sense to conduct your tests underground, you’ll probably avoid crippling sanctions (just don’t be surprised when you can no longer buy anything that might be used in a missile from any other country).

While it’s probably possible for a sufficiently advanced country to build a very simple uranium-based nuclear weapon and have it function with some degree of reliability without testing, any design that uses plutonium, as well as all of the largest, most complicated weapons systems (like the Teller-Ulam design) require either testing, or advanced simulations packages seeded with top-secret data from past tests. Without these tests, your weapon has a very low chance of actually working in the field.

This doesn’t even get into the colossal amount of effort required to develop and test all of the technology necessary to successfully deliver a warhead to a target. Stealth bombers, advanced missiles with MIRV technology, and silently running nuclear armed submarines are all necessary for a country to have full nuclear capability and all of these are impossible to develop in secret.

In summary, there are 6 things a country or non-state actor most do to develop a full, modern nuclear weapons program:

  1. Enrich or acquire a suitable supply of fuel
  2. Design a weapon to make use of that fuel
  3. Miniaturize the weapon
  4. Design robust (capable of surviving an initial nuclear strike) delivery systems for the weapons
  5. Design and test boosted weapons and fusion weapons
  6. Tests these systems, individually and as a whole

There are currently 4 or 5 countries that have completed these steps: China, Russia, America, and India (Israel keeps so much of its nuclear program secret that no one knows if it’s completed all these steps or not). Pakistan, the UK, France, and North Korea have checked off some, but not all boxes on this list, leaving them vulnerable to pre-emptive nuclear attack.

Even if checking off all the boxes is hard, there is a significant risk whenever a country or non-state group checks off any of them. Enriched materials can be used to make dirty bombs, conventional explosive devices that disperse highly radioactive materials (as an area denial or terror tactic) even if a true nuclear device cannot be made. Potentially city destroying nukes require relatively little fissile material or technical expertise. Untested weapons can still work some of the time. The UK, France, and Pakistan all possess a lot of warheads and their inability to protect themselves against a pre-emptive nuclear strike from Russia or the US doesn’t mean they can’t annihilate less powerful countries if they so choose.

All of these represent significant threats to individuals. A small nuke or a large dirty bomb can do a lot of damage if used on the correct target. But so can a conventional weapon. A MOAB or FOAB used on a sporting event would be at least as devastating as a dirty bomb. It is only large arsenals of modern thermonuclear weapons, possessed by countries in numbers large enough that some can reasonably penetrate any countermeasure that represent a true existential threat to humanity. Furthermore, all groups or countries that haven’t completed every single item on my list are vulnerable to having their whole nuclear program destroyed by an adversary before they can use it at all; this severely limits their ability to make threats.

Because of the difficulties inherent in proliferation, the greatest gains to be made in protecting humanity from nuclear weapons must necessarily come from convincing existing nuclear powers to decrease their stocks of weapons or delivery vehicles. This is especially true of Russia and the US, which together possess more than 93% of the world’s nuclear weapons. The challenge will be to do this while maintaining a credible deterrent against any rogue nation that wishes to develop a nuclear weapons program of its own.

Additional Reading: NPT (Full Text), Enriched Uranium, “Weapons Grade” Nuclear Material, Plutonium-239, Nuclear Reprocessing, Proliferation/Breakout Capability, Dirty Bomb, and Nuclear Weapons Testing

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