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A friend of mine gave me a wonderfully quirky and beautiful little book last holiday season, Soviet Space Dogs, written by Olesya Turkina, published by FUEL Design and Publishing. Oleg Gazenko, chief of the dog medical program, with Belka (right) and Strelka (left) at a TASS press conference in 1960.
I had thought I had heard everything there was to hear about Laika, but I was surprised by how much I learned. Put simply, the amount of fissile material you need to start a nuclear reaction varies by the conditions under which it is being considered. The mass of material matters, but only if you specify the conditions under which it is being kept.
Conversely, does this mean that you can’t possibly have 50 kg of uranium (or more) in one place without it detonating? No. In other words, under different conditions, the mass of fissile material that will react varies, and varies dramatically.
Supercriticality, which is what is more important for bomb design (and the initial stages of running a reactor) is when your system produces more than one extra neutron in each generation of fissioning.
The gist of this application is that the red atoms are uranium-235 (or plutonium), and the blue atoms are uranium-238 (or some other neutron-absorbing substance). The goal, if one can put it that way, is to cause a chain reaction that will fission all of the atoms.
My hope is that this kind of visualization will help my students (and others) think through the actual reaction itself a bit more, to help build an intuitive understanding of what is going on, as a remedy to the aspects of a prior language that was created by scientists, diffused publicly, and then got somewhat confused.
If you spend a lot of time on the history of nuclear weapons, you see a lot of mushroom clouds photographs. And yet, most of the time we seem to reach for the same few clouds that we’ve always reached for.
There are actually four shots from this same test that I don’t think most people realize are of a sequence, showing first the brief condensation cloud that formed in the first 20 seconds or so (which exaggerates the width of the actual mushroom cloud, similar to the famous Crossroads Baker photograph), and then tracks the mushroom cloud as it rises. Other clouds that have gotten overused (in my opinion) include Upshot-Knothole Grable, Crossroads Baker, and Upshot-Knothole Badger. Does it matter that we re-use, and sometimes mis-use, the same mushroom clouds over and over again? But it does represent the way in which a lot of our cultural understanding of nuclear weapons has stagnated.
One of the first commercial uses of a fiery mushroom cloud to sell something unrelated to mushroom clouds — in this case, Count Basie’s 1958 album, Basie. Fortunately, I think, these obvious ruts paradoxically create new opportunities for people who want to educate about the bomb.
NotesIt seems to have been made by whomever made this webpage, who seems to say (if Google Translate is to be trusted), that it was rendered using the volumetric rendering software AfterBurn. I first saw this diagram when I was an undergraduate at UC Berkeley, working on a project relating to nuclear weapons — one of my first exposures to this kind of stuff. Looking at it now, I can see also sorts of really serious errors that show the limits of Hansen’s knowledge about Fat Man in 1988. The Princeton crew is also quite active in administering the International Panel on Fissile Materials, which produces regular reports on the quantities of fissile materials in the world. I can’t guarantee it will work with old browsers (it requires a lot of Javascript and transparent PNGs), but please, give it a shot!
I like to think that Chuck Hansen, were he alive today, would appreciate my attempt to take his original diagrammatic representation into a new era. NotesI wrote a very, very, very long paper* in graduate school about the relationship between visual tropes and claims to power through secrecy with relation to the drawing of nuclear weapons.
Last year I wrote a post on here about the story behind the emblem of the International Atomic Energy Agency (IAEA).
The International Atomic Energy Agency (IAEA) has, without much competition, the coolest logo of any part of the UN. Heck, I’ll go so far as to say that they have the coolest logo of any atomic-energy organization in history. The summary version of the post is that the IAEA started informally using the atom with jaunty electron orbits as its emblem in 1957, realized that it was using a symbol for lithium, realized that lithium was fuel for H-bombs, and decided to add an electron to make it beryllium (which is still an important component of nuclear weapons but whatever). This monstrosity got made into a crazy gold-on-blue flag and hoisted up above the United Nations flag at the Third General Conference of the IAEA in 1958. After that they formalized the procedure for approving the emblem of the IAEA and we got the relatively conservative emblem seen above on the current IAEA flag. My only regret about that post is that I couldn’t find a picture of the monstrous flag.
Which is not too far off from what I had guessed it to look like — the most striking difference between the size of the earth at the center. Restricted Data is a blog about nuclear secrecy, past and present, run by Alex Wellerstein, a historian of science at the Stevens Institute of Technology.
Estimated delivery dates - opens in a new window or tab include seller's handling time, origin ZIP Code, destination ZIP Code and time of acceptance and will depend on shipping service selected and receipt of cleared payment - opens in a new window or tab. This amount includes seller specified US shipping charges as well as applicable international shipping, handling, and other fees. By clicking Confirm bid, you commit to buy this item from the seller if you are the winning bidder. By clicking Confirm bid, you are committing to buy this item from the seller if you are the winning bidder and have read and agree to the Global Shipping Program terms and conditions - opens in a new window or tab. By clicking 1 Click Bid, you commit to buy this item from the seller if you're the winning bidder. International Shipping - items may be subject to customs processing depending on the item's declared value. Your country's customs office can offer more details, or visit eBay's page on international trade. Details about  NYC SUBWAY STATION PAPER MODEL, GREAT FOR ALL O SCALE SUBWAY LAYOUTS REALISTIC! It was during a lecture on the Space Race, on Sputnik 2, which carried the dog Laika into space in November 1957. But what can you do, confronted with someone who is taking in the full reality of the fact that the Soviets sent a dog in space with the full knowledge it would die? The American program primarily used apes and monkeys, as they were far better proxies for human physiology than even other mammals. The Soviet scientists reasoned that a dog that could survive on the streets was probably inherently tougher than purebred dogs that had only lived a domesticated life. Laika was the first in orbit, but she was not the first Soviet dog to be put onto a rocket. Turkina talks of the sorrow and guilt of their handlers, who (naturally) developed close bonds with the animals, and felt personally responsible when something went wrong. Laika wasn’t really meant to be the first dog in space — she was the understudy of another dog who had gotten pregnant just before. Laika was just listed as an experimental animal in the Sputnik 2 satellite. Rather, it was the Western press, specifically American and British journalists, that got interested in the identity, and fate, of the dog. A friend of mine, Slava Gerovitch, has written a lot about the Soviet philosophy of space rocket design, and on the low regard the engineers who ran the program had for human passengers and their propensity for messing things up. But it’s a very tricky concept, one often poorly deployed and explained, and the result, I have found while teaching and while talking to people online, is an almost universal confusion about what it means on a physical level. For one thing, talking about the mass can help you get a sense of the size of the problem when fissile material is scarce and hard to produce (producing fissile material consumed 80% of the Manhattan Project’s budget). Because under different conditions, any given form of fissile material will have different critical masses.

If your uranium is fashioned not into a solid sphere, but a cylinder, or is a hollow sphere, or has neutron-absorbing elements (i.e. The problem wasn’t the mass of the core, it was that Slotin inadvertently changed the state of the system (by accidentally letting the reflector drop onto it completely when his screwdriver slipped), which took a safe, non-critical assemble of plutonium and moved it into a briefly-critical state. So if our uranium atom splits, produces 2 neutrons, and each of those go on to split more atoms, we’re talking about getting two neutrons for every one we put into the system. You need it to be supercritical, and to stay supercritical long-enough that a lot of energy is released. Processing.js is a language that makes physics visualizations (among other things) pretty easy. None of the numbers used have any physically-realistic quality to them, and real atomic bombs rely on the fissioning of trillions of atoms in a 3D space (whereas if you try to increase the number of atoms visible to 1,000, much less 10,000, your browser will probably slow to a crawl, and this is just in 2D space!).4 And this simulator does not take into account the effects of fission products, among other things. There were over 500 atmospheric nuclear tests conducted during the Cold War, and most of these were photographed multiple times. How many books, for example, have this shot of the Castle Romeo mushroom cloud on their cover?
The same visuals of the bomb, over and over again, mimic the same stories we tell about the bomb, over and over again. It is one of the ironies of history that the more firmly entrenched an existing narrative gets, the more interested people are in compelling counter-narratives. It features 12 unusual photographs of nuclear detonations, all of which I have carefully cleaned up to remove scratches and dust spots. And because 2015 is the 70th anniversary of the Trinity test, I have also reissued last-year’s Trinity test calendar. Unmaking the Bomb: A Fissile Material Approach to Nuclear Disarmament and Non-Proliferation, by Harold Feiveson, Alex Glaser, Zia Mian, and Frank von Hippel, was recently published by MIT Press. I had checked out pretty much every book on the subject that was in the Berkeley library system, which meant I found lots of unexpected, un-searched-for things serendipitously amongst the stacks.
An obvious one is that it is missing the aluminum pusher which sits in between the tamper and the high explosives.
The authors outline a series of steps that could be taken to reduce the amount of fissile materials in the world, which they see as a bad thing both for non-proliferation (since a country with stockpiles of fissile materials can basically become a nuclear power in a matter of weeks), disarmament (since having lots of fissile materials means nuclear states could scale up their nuclear programs very quickly if they chose to), and anti-terrorism (the more fissile materials abound, the more opportunities for theft or diversion by terrorist groups). Numbers are, as always, hard for me to visualize, so I have been experimenting with ways of visualizing them effectively. The small blue-ish blocks represent the approximate volume of 50 kg of highly-enriched uranium (which is on order for what you’d need for a simple gun-type bomb, like Little Boy), and the small silver-ish blocks are the same for 5 kg of separated plutonium (on order for use in a first-generation implosion weapon). The cubes were quite large but didn’t quite convey the sense of scale — it was too hard for my brain, anyway, to make sense of how little material you needed for a bomb and put that into conversation with the size of the cube.
As one might imagine, when I was learning to use Blender, the first thing I thought to try and model was Fat Man and Little Boy, because they are subjects dear to my heart and they present interesting geometric challenges. And I like to think that this kind of visualization can help people, especially non-scientists (among which I count myself), wrap their heads around the tricky technical aspects of a controversial and problematic technology. I have never quite edited it into a publishable shape and I fear that it would be very hard to do anything with given the fact that you really need to reproduce the diagrams to see the argument, and navigating through the copyright permissions would probably take a year in and of itself (academic presses are really averse to the idea of relying on “fair use“), and funds that nobody has offered up! Eric Reber, a radiation safety specialist at the IAEA,had read my previous blog post on this topic and then noticed framed documents on the walls at IAEA Headquarters regarding the evolution of the IAEA emblem.
The first one has a cluttered, cheesy quality that would not have reproduced well at small sizes at all; the second one has unfortunately testicular overtones.
As someone who dabbles in graphic design, I am impressed with how something beautiful and brilliant almost turned out to be something terrible and tacky. Import charges previously quoted are subject to change if you increase you maximum bid amount. This model was never offered in a retail box or package Not suitable for children under 3 years old Each model is meticulously finished for unsurpassed quality. I told them about how the Soviets initially said she had lived a week before expiring (it was always intended to be a one-way trip), but that after the USSR had collapsed the Russians admitted that she had died almost immediately because their cooling systems had failed. I just believe that they connect with people on a deeper level than really any other animal.
And, Laika aside, a lot of them went up and came back down again, providing actually useful information about how organisms make do while in space, and allowing us to have more than just relentlessly sad stories about them. He collected a huge mass of odd Soviet (and some non-Soviet) pop culture references to the Soviet space dogs, and they commissioned Turkina, a Senior Research Fellow at the State Russian Museum, to write the text to accompany it.
Turkina counts at least 29 dogs prior to Laika who were attached to R-1 and R-2 rockets (both direct descendants of the German V-2 rockets), sent up on flights hundreds of miles above the surface of the Earth starting in 1951.
Some of the surviving dogs got to live with these handlers when they retired from space service. One sees this very clearly in most of the Soviet depictions of Laika — proud, facing the stars, serious. Plus, Belka and Strelka were cute. They could be trotted out at press conferences, on talk shows, and were the subjects of a million adorable pictures and drawings. Gagarin had about as much control over his satellite as Belka and Strelka did over theirs, because neither were trusted to actually fly a satellite. There is also just something so emblematic of the space age about the idea of putting dogs into satellites — taking a literally pre-historic human technology, one of the earliest and most successful results of millennia of artificial breeding, and putting it atop a space-faring rocket, the most futuristic technology we had at the time. And it can also help you when talking about safety questions — about avoiding a nuclear reaction until you absolutely want on.
In its current form — unreflected, at normal density, in a ring-shape that prevents any neutrons from finding too many atoms to fission with — it is relatively innocuous. So if you put a heavy, neutron-reflecting tamper around the uranium, you can get away with around 10 to 15 kg of uranium-235 for a bomb — a factor of 3-5X less mass than you thought you needed.
This produced no explosion, but enough radiation to be fatal to Slotin and damaging to others in the room.
Neutrons enter the system (either from a neutron source, spontaneous fissioning, or the outside world). Which is to say, each neutron that goes into the material will get replaced by at least another neutron.
If a neutron hits a red atom, it has a chance to cause it to fission (and a chance to just bounce off), which releases more atoms (and also pushes nearby atoms away). But you can manipulate a whole host of variables using the menu at the right, including adding a neutron reflector, changing the number of atoms and their initial packing density, the maximum number of neutrons released by the fission reaction, and even, if you care to, changing things like the lifetimes of the neutrons, the likelihood of the neutrons just scattering off of atoms, and whether the atoms will spontaneously fission or not. An animated version is circulating on YouTube — the physics is all wrong regarding the fireball rise, the stem, etc., and the texturing is off. I do admit finding the confusion about this one amusing, especially when it is mislabeled as a British test. Glaser, who does some pretty far-out work at the Nuclear Futures Lab (among other things, he has been working on really unusual ways to verify weapons disarmament without giving away information about the bombs themselves — a really tricky intersection of policy, technical work, and secrecy), asked me if I would help them design the cover, knowing that I like to both dabble in graphic arts as well as bomb-related things.
The original drawing was made many times larger than it was going to be in the book — it was four feet long! There are other issues relating to the most sensitive parts of the core, things that John Coster-Mullen has spent several decades now working out the details of. At bottom, a screenshot from the 1989 film Fat Man and Little Boy shows Oppenheimer pondering essentially the same image.
Rendering it in terms of bomb-sized materials does the trick a bit better, I think, and helps emphasize the overall political argument that the Unmaking the Bomb authors are trying to get across: you can make a lot of bombs with the materials that the world possesses. They are not so free-form and difficult as rendering something organic (like a human being, which is hard), but they are also not simply combinations of Archimedean solids.

It is not truly 3D, as you will quickly see — it uses pre-rendered layers, because 3D is still a tricky thing to pull off in web browsers — but it is maybe the next best thing. But maybe someday I will find some way to use it other than as a source for anecdotes for the blog.
Among them were two different versions of the monstrous emblem, along with text noting that they had apparently been missing from the IAEA Archives until fairly recently, when copies were given as donations. The Sollinger designs overlaid so much symbolism onto the IAEA’s emblem that the whole thing almost tipped over. If you reside in an EU member state besides UK, import VAT on this purchase is not recoverable. We had this book on our coffee table for several months before I decided to give it a spin, and I really enjoyed it — it’s much more than a lot of pretty pictures, though it is that, in spades, too.
According to one participant in the program, one of the leading scientists had looked into using monkeys, talking with a circus trainer, and found out that monkeys were terribly finicky: the training regimes were harder, they were prone to diseases, they were just harder in general to care for than dogs.
But when the surviving dogs eventually expired, they would sometimes end up stuffed and in a museum. It was only after discussion began in the West that Soviet press releases about Laika came out, giving her a name, a story, a narrative. Once again, Belka and Strelka were not meant to be the dogs for that mission: an earlier version of the rocket, kept secret at the time, exploded during launch a few weeks earlier, killing the dogs Lisichka and Chaika.
When Strelka had puppies, they were cheered as evidence that biological reproduction could survive the rigors of space, and were both shown off and given as prized gifts to Soviet officials. The contrast between the engineering attitudes of the Soviet Vostok and the American Mercury program is evident when you compare their instrument panels. At right, you see what happened when the pieces got close enough to start a critical reaction — not a massive explosion (thank goodness), but enough energy output to damage the machine, and to push those pieces of uranium far enough from each other that they could no longer react.
If your uranium-235 is dissolved in water, it takes very low masses to start a self-sustaining reaction — a dangerous condition if you didn’t mean to start one! And, of course, there are also impurities — the amount of uranium-238 in your uranium-235 will increase the size of any critical mass calculation.
It’s not a fixed number, unless you also fix all of your assumptions about the conditions under which it is taken place. At normal, room-temperature densities, a solid sphere of 6.2 kg of plutonium is not critical. But both the question of criticality and efficiency are really one and the same phenomena — if you understand the underlying physical process on an intuitive level. If they are absorbed by a uranium-235 nucleus, they have a chance of making it undergo fission. Since neutrons move very quickly, and each reaction takes place very quickly (on the order of a nanosecond), this becomes a very large number of neutrons very quickly. Obviously it is a little more arcane than just that, but if you have experience programming, that is more or less how it works.
It gets used, however, for all sorts of things — like the Cox Report’s 1999 allegations about China stealing advanced (much lower-yield) thermonuclear warhead designs, or illustrating Soviet nuclear weapons, or illustrating (most incorrectly) nuclear terrorism (which would not look like this at all).
Apparently a lot of people have been fooled, though.1 There is film of the actual Tsar Bomba explosion, and one can readily appreciate how different it is. And these fit the bill, except maybe the fake one, which will turn off anyone who can spot a fake. After being finished, it was reduced down to the size on the page in the book, so that it just looked like it was packed with fine detail. Hansen, in his later Swords of Armageddon, corrected many of these errors, but he never made a diagram that good again.
One of my goals for this academic year is to develop a scaled, 3D-printed model of the Fat Man bomb, with all of the little internal pieces you’d expect, based on the work of John Coster-Mullen. It has more detail than the one on the cover of the book, but you can filter a lot of it on and off.
An atom that knows how to have fun, even when it’s doing serious business, like investigating your nuclear program.
For once, sending the thing to committee seems to have improved the outcome, and we got a sleek, stylish atom for the ages instead. And a fate: they talked about her as a martyr to science, who would be kept alive for a week before being painlessly euthanized. And knowing that the critical mass is so many kilograms of fissile material, as opposed to so many tons, was an early and important step in deciding that an atomic bomb was feasible in the first place.
But it’s more complicated than that, and this is where I think focusing on the mass can lead people astray. In other words, if you assembled 50 kg of uranium-235 into a solid sphere, with nothing around it, at normal atmospheric conditions, it will start a self-sustaining chain reaction.
And it may be possible, under very carefully-developed conditions, to make a bomb with even smaller masses. Increase its density by 2.5X through the careful application of high explosives, however, and suddenly that is at least one critical mass of plutonium. Such is a bomb: an exponential chain reaction that goes through enough reactions very quickly to release a lot of energy. Each fission reaction produces on average 2.5 more neutrons, but depending on the setup of the system, most or all of those may not find another fissile nuclei to interact with. Some of them are physical constants, things pertaining to the nature of the atoms themselves.
More details about the calendars and other nuclear delights at my updated Calendars, gifts, tchotchkes page.
I’ve never done 3D-printing before, but some of my new colleagues in the Visual Arts and Technology program here at the Stevens Institute of Technology are experienced in the genre, and have agreed to help me learn it. Again, the point is to emphasize the centrality of the fissile material, but to also show all of the apparatus that is needed to make the thing actually explode.
The secrecy of the program, of course, pervades the entire story of the Soviet side of the Space Race, and serves as a marked contrast with the much more public-facing US program (the consequences of which are explored in The Right Stuff, among other places).
It probably would not produce an explosion of great violence — the uranium sphere would probably just blow itself a few feet apart (and irradiate anyone nearby). If, however, the system is set up in a way that means that the replacement rate is more than one neutron — if every neutron that enters or is created ends up creating in turn at least two neutrons — then you have a supercritical system, with an exponentially-increasing number of neutrons.
By coming back alive, they fed dreams of an interstellar existence for mankind that were particularly powerful in the Soviet context. The relative crudity of the Little Boy bomb meant that only about 1% of its fissile material reacted — it was many times less efficient, even though it had roughly 10X more fissile material in it than the Fat Man bomb. The overall scene, however, is rendered in Blender, using volumes computed by WolframAlpha.
If we’ve already got a lot of neutrons in there, this will generate a lot of energy, which is essentially how a nuclear reactor works once it is up and running.
The concept of the critical mass, here, really doesn’t illuminate these differences, but an understanding of how the critical reactions work, and how the overall system is set up, does.

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