Posts Tagged ‘Graphic design’

Visions

Critical mass

Friday, April 10th, 2015

When we talk about how nuclear weapons work, we inevitably mention the “critical mass.” This is the amount of fissile material you need to create a self-sustaining nuclear reaction. 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.

One of the ways in which the critical mass is visually explained in Glasstone and Dolan's The Effects of Nuclear Weapons (1977 edn.). Want it on a t-shirt? I've got you covered.

One of the ways in which the critical mass is visually explained in Glasstone and Dolan’s The Effects of Nuclear Weapons (1977 edn.). Want it on a t-shirt? I’ve got you covered.

Where does the term come from? In the Smyth Report released in August 1945, the term “critical size” is used almost universally, while “critical mass” is used exactly once (and parenthetically, at that). A more interesting term, the “critical condition,” is used in a few places. The Los Alamos Primer, from 1943, uses critical “radius,” “volume,” “conditions,” in addition to “mass.” The MAUD Report, from 1941, uses critical “size,” “value,” and “amount” — not mass. The Frisch-Peirels memorandum, from 1940, uses critical “radius,” “size,” and “condition.” Leo Szilard’s pre-fission, 1935 patent on chain reacting systems uses the terms critical “thickness,” and “value,” not mass. This is not to imply that people didn’t use the term “critical mass” at the time — but it was one term among many, not the only term. The earliest context I have found it being used extensively comes from a paper in 1941, where it was being used specifically to talk about whether masses of fissile material could be made to explode on demand and not before.1

Why use “critical mass” instead of other terms? 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). And it can also help you when talking about safety questions — about avoiding a nuclear reaction until you absolutely want on. So you don’t want to inadvertently create a critical mass. 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.

A 5.3 kg ring of 99.96% pure plutonium-239. Under some conditions, this is enough to produce a significant explosive output. 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.

A 5.3 kg ring of 99.96% pure plutonium-239. Under some conditions, this is enough to produce a significant explosive output. 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.

What I don’t like about the term, though, is that it can easily lead to confusion. I have seen people assert, for example, that you need a “critical mass” of uranium-235 to start a nuclear reaction. Well, you do — but there is no one critical mass of uranium-235. In other words, used sloppily, people seem to often think that uranium-235 or plutonium have single values for their “critical mass,” and that “a critical mass” of material is what you use to make a bomb. But it’s more complicated than that, and this is where I think focusing on the mass can lead people astray.

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. Because under different conditions, any given form of fissile material will have different critical masses.

I’ve seen people (mostly online) want to talk about how nuclear weapons work, and they look up what “the” critical mass of uranium-235 is, and they find a number like 50 kg. They then say, OK, you must need 50 kg to start a nuclear reaction. But this is wrong. 50 kg of uranium-235 is the bare sphere critical mass of uranium-235. 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. 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). But once blown apart, the reaction would stop. Not a bomb.

The Godiva Device, a "naked" (get it?) critical assembly used as a pulsed nuclear reactor at Los Alamos. A 54 kg near-bare sphere of 93.7% enriched uranium separated into three pieces. At left, it is separated safely — no reaction. 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.

The Godiva Device, a “naked” (get it?) critical assembly used as a pulsed nuclear reactor at Los Alamos. A 54 kg near-bare sphere of 93.7% enriched uranium separated into three pieces. At left, it is separated safely — no reaction. 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. The workers were fortunately a safe distance away.

So does that mean that 50 kg of uranium-235 is a important number in and of itself? Only if you are assembling solid spheres of uranium-235.

Is 50 kg the amount you need for a bomb? No. You can get away with much smaller numbers if you change the conditions. 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. 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 it may be possible, under very carefully-developed conditions, to make a bomb with even smaller masses. (The bare-sphere critical mass of plutonium is around 10 kg, but apparently one can get a pretty good bang out of 3-4 kg of it, if not less, if you know what you are doing.)2

Conversely, does this mean that you can’t possibly have 50 kg of uranium (or more) in one place without it detonating? No. 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. boron) embedded in it, then you can (if you know what you are doing) exceed that 50 kg number without it reacting. 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.

In other words, under different conditions, the mass of fissile material that will react varies, and varies dramatically. These different conditions include different geometries, densities, temperatures, chemical compositions/phases, and questions about whether it is embedded into other types of materials, whether there are neutron-moderating substances (i.e. water) present, enrichment levels, and so on. It’s not a fixed number, unless you also fix all of your assumptions about the conditions under which it is taken place.

Re-creation of Slotin's fatal experiment with the third core. (Source: Los Alamos)

Re-creation of Louis Slotin’s fatal experiment with the third plutonium core. 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. This produced no explosion, but enough radiation to be fatal to Slotin and damaging to others in the room.

The classic example of this, of course, is the implosion bomb design. The bare sphere critical mass of plutonium-239 is 10 kg. The Nagasaki bomb contained 6.2 kg of plutonium as its fuel. At normal, room-temperature densities, a solid sphere of 6.2 kg of plutonium is not critical. 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. Even this is something of an oversimplification, because it’s not just the density that matters: the allotropic (chemical) phase of plutonium, for example, affects its critical mass conditions (and plutonium is notorious for having an unusual number of these phases), and the Nagasaki bomb also included many other useful features meant to help the reaction along like a neutron initiator (which gave it a little shot of about 100 neutrons to start things off), and a heavy, natural-uranium tamper.

What I dislike about the term “critical mass,” as well, is that it can serve to obscure the physical process that defines “criticality.” It can make it seem like reactivity is a function of the mass alone, which is wrong. Worse, it can keep people from realizing why the mass matters in the way it does (among other things). And this can lead to confusion on questions like, “how much explosive power does a critical mass release?” The answer is… it has nothing to do with the critical mass per se. That is a question of bomb efficiency, which can seem like a secondary, separate question. 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.

Criticality, the “critical condition,” is defined as the point at which a chain reacting system becomes self-sustaining. So we can imagine a whole sea of uranium-235 atoms. Neutrons enter the system (either from a neutron source, spontaneous fissioning, or the outside world). If they are absorbed by a uranium-235 nucleus, they have a chance of making it undergo fission. That fission reaction will produce a random number (2.5 on average) of secondary neutrons. To be critical, enough of these neutrons will then have to go on to find other uranium nuclei to keep the overall level of neutrons (the “neutron economy”) constant. If that total number of neutrons is very low, then this isn’t very interesting — one neutron being replenished repeatedly isn’t going to do anything interesting. 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.

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. 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. This is an exponentially-growing number of neutrons. 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. Such is a bomb: an exponential chain reaction that goes through enough reactions very quickly to release a lot of energy.

The Trinity Gadget - Sectional View

A sectional view of a rendering of the Trinity “Gadget” I made. The 6.2 kg sphere of plutonium (the second-to-last sphere in the center, which encloses the small neutron initiator) is a safe-to-handle quantity by itself, and only has the possibility of becoming super-critical when the high explosives compress it to over twice its original density. Sizes are to scale.

So what are the conditions that produce these results? Well, it’s true that if you pure enough fissile material in one place, in the right shape, under the right conditions, it’ll become critical. Which is to say, each neutron that goes into the material will get replaced by at least another neutron. It will be a self-sustaining reaction, which is all that “criticality” means. 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. 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. This is what can lead to explosions, as opposed to just generating heat.

In a bomb, you need more than just a critical reaction. You need it to be supercritical, and to stay supercritical long-enough that a lot of energy is released. This is where the concept of efficiency comes into play. In theory, the Fat Man’s 6.2 kg of plutonium could have released over 100 kilotons worth of energy. In practice, only about a kilogram of it reacted before the explosive power of the reaction separated the plutonium by enough that no more reactions could take place, and “only” released 20 kilotons worth of energy. So it was about 18% efficient. 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 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.

This understanding of criticality is more nuanced than a mere mass or radius or volume. So I prefer the alternative phrasing that was also used by weapons designers: “critical assembly” or “critical system.” Because that emphasizes that it’s more than one simple physical property — it’s about how a lot of physical properties, in combination with engineering artifice, come together to produce a specific outcome.

I’ve been playing around with the scripting language Processing.js recently, in my endless quest to make sure my web and visualization skills are up-to-date. Processing.js is a language that makes physics visualizations (among other things) pretty easy. It is basically similar to Javascript, but takes care of the “back end” of graphics to a degree that you can just say, “create an object called an atom at points x and y; render it as a red circle; when it comes into contact with another object called a neutron, make it split and release more neutrons,” and so on. Obviously it is a little more arcane than just that, but if you have experience programming, that is more or less how it works. Anyway, I had the idea earlier this week that it would be pretty easy to make a simple critical assembly “toy” simulation using Processing, and this is what I produced:

Critical Assembly Simulator

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). Clicking on an atom will cause it to fission, and clicking on the “fire neutron initiator” button will inject a number of neutrons into the center of the arrangement. 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). If it hits a blue atom, it has a chance to be absorbed (turning it purple).

The goal, if one can put it that way, is to cause a chain reaction that will fission all of the atoms. As you will see from clicking on it, in its initial condition it is hard to do that. 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. If you have a reflector added, you can also click the “Implode” button to make it compress the atoms into a higher density.3

The progress of a successful reaction using an imploded reflector. The little yellow parts are a "splitting atom" animation which is disabled by default (because it decreases performance).

The progress of a successful reaction using an imploded reflector. The little yellow parts are a “splitting atom” animation which is disabled by default (because it decreases performance).

This is not a real physical simulation of a bomb, obviously. 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. But I like that it emphasizes that it’s not just the number of atoms that determines whether the system is critical — it’s not just the mass. It’s all of the other things in the system as well. Some of them are physical constants, things pertaining to the nature of the atoms themselves. (Many of these were constants not fully known or understood until well after 1939, which is why many scientists were skeptical that nuclear weapons were possible to build, even in theory.) Some of them are engineering tricks, like the reflector and implosion.

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. “Critical mass” isn’t a terrible term. It has its applications. But when it can lead to easy misunderstandings, the language we choose to use matters.

Notes
  1. E.g. “Can system be controlled safely by dividing mass into two parts? Yes. We believe that it is possible with suitable technical supervision to assemble masses which will be known fractions of the critical mass and which will not explode during the assembly.” The authorship of the report is apparently several members of the Uranium Committee, but their specific names are unlisted. “Fast neutron chain reactions — Summary of discussion on recommendations of the Sub-section on theoretical aspects on October 24, 1941,” (24 October 1941), copy in Bush-Conant File Relating the Development of the Atomic Bomb, 1940-1945, Records of the Office of Scientific Research and Development, RG 227, microfilm publication M1392, National Archives and Records Administration, Washington, D.C., n.d. (ca. 1990), Reel 10, Target 21, Folder 162A, “Reports — Chain Reactions [1941].” []
  2. On the “how low can you go” question, I have found table A.1 in this report useful:International Panel on Fissile Material, “Global Fissile Material Report 2013: Increasing Transparency of Nuclear Warhead and Fissile Material Stocks as a Step toward Disarmament,” Seventh annual report of the International Panel on Fissile Material (October 2013). There is documentary evidence suggesting the Soviets managed to weapons with cores as little as 0.8 kg of plutonium, and got significant (e.g. >1 kiloton) yields from them. []
  3. For those who want it, the source code is here. It is sparsely commented. It is written, again, in Processing.js. []
  4. Just to put this into perspective, 1 kg of plutonium-239 is ~2.5 x 1024 atoms. []
Visions

Mushroom clouds strange, familiar, and fake

Monday, December 1st, 2014

If you spend a lot of time on the history of nuclear weapons, you see a lot of mushroom clouds photographs. There were over 500 atmospheric nuclear tests conducted during the Cold War, and most of these were photographed multiple times. (There were over 50 dedicated cameras at the Trinity test, as one little data point.) The number of unique photographs of nuclear explosions must number in the several thousands.

Castle Romeo

And yet, most of the time we seem to reach for the same few clouds that we’ve always reached for. How many books, for example, have this shot of the Castle Romeo mushroom cloud on their cover? Romeo was an American H-bomb test from 1954, 11 megatons in yield. 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). It’s a great photo (dramatic, red, well-framed), but it’s not a generic mushroom cloud — it is a really high yield weapon, and arguably ought to only be used to illustrate very high yield weapons.

OK, I’m a pedant about this kind of thing. I get annoyed with poorly-used mushroom cloud photos, and repetitive photos, because there are just so many good options out there if the graphic designers in question would just search beyond the first thing that comes up when you Google “mushroom cloud.” But re-using known clouds is not as bad as, say, mistaking a fake, computer-generated mushroom cloud for a real one.

Fake Tsar Bomba

This photo is often labeled as the “Tsar Bomba” cloud and it is not even an actual photograph of a nuclear test — it is a CGI rendering, and not even a very good one. I don’t think you even have to be a nuke wonk to recognize that, and that people’s CGI-savvy would be better than this, but I guess 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. 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.

The above photo is also sometimes labeled as the “Tsar Bomba,” and was recently featured on the cover a book about the British atomic bomb, labeled as a British thermonuclear weapon. It is actually a French nuclear weapon, specifically the test dubbed “Licorne,” a 914 kiloton thermonuclear shot detonated in 1970 at the Fangataufa atoll in French Polynesia. I do admit finding the confusion about this one amusing, especially when it is mislabeled as a British test. (As an aside: I do not blame authors for the photos on their book covers, because I know they often don’t have anything much to do with the cover images.)

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. When you resize them to the same scale (more or less), you can see that they are not four different shots at all, just differently timed photographs of the evolution of a single shot’s mushroom cloud:

There is also a film of the test, though the quality isn’t that great. The whole sequence represents less that a minute of the bomb detonation; as I’ve noted previously, most of our photos of mushroom clouds are from the first minute or so after their detonation, and they can get pretty unfamiliar if you watch the cloud evolve for longer than that.

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? In a material sense it does not, because the people who use/misuse these clouds are really not using them to make a sophisticated visual or intellectual argument. Rather, they have chosen a “scary mushroom cloud” image for maximum visual effect. And these fit the bill, except maybe the fake one, which will turn off anyone who can spot a fake.

But it does represent the way in which a lot of our cultural understanding of nuclear weapons has stagnated. The same visuals of the bomb, over and over again, mimic the same stories we tell about the bomb, over and over again. Culturally, there is a deep “rut” that has been carved in how we talk and think around nuclear weapons, a sort of warmed-over legacy of the late Cold War. I am sometimes astounded by how deep, and how deeply held, this rut is — on Reddit, for example, people will fight vehemently over the question of dropping of the atomic bomb, sticking exclusively to positions that were argued about 20 years ago, the last time this stuff was “hot.” They aren’t aware that the historiography has moved quite a distance since then, because you’d never know that from watching or reading most historical discussions of the bomb in mainstream media.

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.

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. The test is Operation Plumbbob, shot Hood.

Fortunately, I think, these obvious ruts paradoxically create new opportunities for people who want to educate about the bomb. 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. The fact that there is a rut in the first place means that there is already a built-in audience (as opposed to history that people just don’t know anything about), and if you can find something new to say about that history, then they’re interested.

“New” here can also mean “new to them,” as opposed to “new to people who spend their lives looking at this stuff.” This is what I was talking about when I was quoted in the New York Times a few weeks ago — things that known to scholars are being discovered and re-discovered by mass audiences who are surprised to find how many different and apparently novel photographs and stories are out there.

As an aside, if I were going to give graphic designers a set of “mushroom cloud use guidelines,” they would be, more or less: 1. don’t use the first cloud you find (there are so many unusual and dramatic ones out there, if you poke around a little bit); 2. don’t use extremely historically-specific clouds (i.e. Hiroshima and Nagasaki) as generic images; 3. don’t use multi-megaton shots (i.e. giant red/orange/yellow cloud fireballs) if you are talking about kiloton-range weapons (i.e. terrorist bombs); and 4. if you are going to label something as British, make sure it is not actually French!


Untitled

As part of my annual contribution to people becoming better acquainted with “new” mushroom cloud photographs, I have released a new and updated version of my Nuclear Testing Calendar for 2015. It features 12 unusual photographs of nuclear detonations, all of which I have carefully cleaned up to remove scratches and dust spots. All of the images are courtesy of Los Alamos National Laboratory.

Here is a little preview of some of the unusual clouds you will find in this calendar:

2015 Nuclear Testing Calendar preview

There are also over 60 nuclear “anniversaries” noted in the calendar text itself. And because 2015 is the 70th anniversary of the Trinity test, I have also reissued last-year’s Trinity test calendar. Both calendars are being offered for $18.99. The site that publishes them, Lulu.com, also often has a lot of coupons on a regular basis — please feel free to take advantage of them! All proceeds go to offsetting the costs of my web work. More details about the calendars and other nuclear delights at my updated Calendars, gifts, tchotchkes page.

Notes
  1. It 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. []
Visions

Visualizing fissile materials

Friday, November 14th, 2014

I’ve had some very favorable interactions with the people at the Program on Science and Global Security at Princeton University over the years, so I’m happy to announce that four of the faculty have collaborated on a book about the control of fissile material stockpiles. 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. 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. Here is what we came up with, in both its rendered and final form:

Unmaking the Bomb cover and render

The “exploded” bomb here is obvious a riff on the Fat Man bomb, simplified for aesthetic/functional purposes, and was created by me using the 3-D design program Blender. (The rest of the cover, i.e. the typography, was designed by the art people at MIT Press.) The idea behind the image was to highlight the fact that the fissile material, the nuclear core of the bomb, made up a very small piece of the overall contraption, but that its importance was absolutely paramount. This is why the non-nuclear parts of the bomb are rendered as a sort of grayish/white “putty,” and the core itself as a metallic black, levitating above.

The original idea, proposed by Glaser, was to do sort of a modern version of a drawing that appears in Chuck Hansen’s U.S. Nuclear Weapons: The Secret History (Aerofax: 1988). Hansen’s image is a thing of beauty and wonder:

1988 - Chuck Hansen - Fat Man

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. 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. (This is something that I think has been lost, or at least not replicated, with increased reliance on digital sources.) I saw this diagram and thought, “Wow! That’s a lot of information about an atomic bomb! I wonder how he got all of that, and how much of it is real and how much is made up?” I don’t want to say this diagram is what made me want to study nuclear secrecy — origins and interests are always more complicated than that, and a close friend of mine recently reminded me that even in elementary school I used to talk about how nuclear bombs were made, armed with the beautiful-but-highly-inaccurate drawings from Macaulay’s The Way Things Work), but it did play a role.

Eventually I did track down a lot of information about this particular diagram. I found Hansen’s own original sketch of it (in his papers at the National Security Archive) that he gave to the artist/draftsman who drew the piece, Mike Wagnon:

Chuck Hansen Fat Man sketch

I also tracked down Wagnon, some years back now. He told me how he drew it. The original drawing was made many times larger than it was going to be in the book — it was four feet long! 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. He also confirmed for me what I had come to suspect, that the diagrams in Hansen’s book, as Wagnon put it to me in 2004, “advertise an accuracy they do not have.” A lot of it was just deduced and guessed, but when you draw it like an engineering diagram, people assuming you know what you’re doing.1

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. An obvious one is that it is missing the aluminum pusher which sits in between the tamper and the high explosives. 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. Hansen, in his later Swords of Armageddon, corrected many of these errors, but he never made a diagram that good again. As an aside, Wagnon’s version of Little Boy — which we also now know, because of Coster-Mullen, has many things wrong — was the source of the “blueprint” for the bomb in the 1989 film Fat Man and Little Boy:

At top, Wagnon's diagram of Little Boy from Hansen's 1988 U.S. Nuclear Weapons. At bottom, a screenshot from the 1989 film, Fat Man and Little Boy, shows Oppenheimer pondering essentially the same image.

At top, Wagnon’s diagram of Little Boy from Hansen’s 1988 U.S. Nuclear Weapons. At bottom, a screenshot from the 1989 film Fat Man and Little Boy shows Oppenheimer pondering essentially the same image.

Anyway, I am getting off the thread a bit. Unmaking the Bomb, aside from having an awesome cover, is about fissile materials: enriched uranium and separated plutonium, both of which can be readily used in the production of nuclear weapons. 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).

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. Numbers are, as always, hard for me to visualize, so I have been experimenting with ways of visualizing them effectively. This is a visualization I cooked up this week, and I think it is mostly effective at conveying the basic issues regarding fissile materials, which is that the stockpiles of them are extremely large with respect to the amounts necessary to make weapons:

world fissile material stockpiles

Click the image to enlarge it. 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). One can play with the numbers there a bit but the rough quantities work out the same. Each of the “big” stacks contain 1,000 smaller blocks. All references to “tons” are metric tons (1,000 kg). The “person” shown is “Susan” from Google SketchUp. The overall scene, however, is rendered in Blender, using volumes computed by WolframAlpha.

I made this visualization after a few in which I rendered the stockpiles as single cubes. 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. 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. If you want the run-down on which countries have these materials (spoiler: it’s not just the ones with nuclear weapons), check out the IPFM’s most recent report, with graphs on pages 11 and 18.

To return to the original thread: the bomb model I used for the cover of Unmaking the Bomb is one I’ve been playing with for a while now. 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. 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. 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. 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. (To learn a new technology, one always needs a project, I find. And I find my projects always involve nuclear weapons.)

For a little preview of what the 3D model might end up looking like, I expanded upon the model I developed for the Unmaking the Bomb cover when I helped put together the Unmaking the Bomb website. Specifically, I put together a little Javascript application that I am calling The Visual Atomic Bomb, which lives on the Unmaking the Bomb website:

The Visual Atomic Bomb screenshot

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! By hovering your mouse over the various layer names, it will highlight them, and you can click the various buttons (“hide,” “show,” “open,” “close,” “collapse,” “expand,” and so on) to toggle how the various pieces are displayed. 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. It has more detail than the one on the cover of the book, but you can filter a lot of it on and off. 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.

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. 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.

Notes
  1. I 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. 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! But maybe someday I will find some way to use it other than as a source for anecdotes for the blog. *OK, I’ll own up to it: it was 93 pages long (but only 62 pages of text!) when I turned it in to the professor. I was told I should either turn it into a long article or a short book. []
Visions

The lost IAEA logo

Friday, September 26th, 2014

Last year I wrote a post on here about the story behind the emblem of the International Atomic Energy Agency (IAEA). To quote from it:

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. I mean, check this thing out:

IAEA flag

It’s not only an atom, it’s an atom with style. It’s got a classic late-1950s/early-1960s asymmetrical, jaunty swagger. Those electrons are swinging, baby! This is an atom for love, not war, if you dig what I’m saying. An atom that knows how to have fun, even when it’s doing serious business, like investigating your nuclear program. The James Bond of atoms.

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). While they were sprucing it up a bit, they decided it might be fun to add on a bunch of other things as well:

Once the process of altering the emblem had started, further suggestions were made and soon a design evolved in which the central circle had been expanded into a global map of the world and five of the eight loops formed by the ellipses contained respectively: a dove of peace with an olive branch; a factory with smoking chimneys and surcharged with a train of three gear wheels; a microscope; two spears of grain; and finally a caduceus, to symbolise respectively the peaceful, industrial, research, agricultural and medicinal uses of atomic energy.

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. As I wrote then,

Apparently in UN-world, this was seen as a major scandal. A representative of the UN Secretary General, Dag Hammarskjöld, saw it, flipped out, and had it immediately removed. And it was never seen again. 

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. I even contacted the IAEA and everything. No luck. The best I could do was an artist’s interpretation:

IAEA 1958 logo (artist's interpretation)

Which seemed a bit ridiculous but I thought it matched the description pretty well.

Well, guess what: the monstrous emblem has been found. 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. 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. Eric very helpfully took some photos of them and sent them to me in an e-mail.

They were designed by one Manfred Sollinger, about whom I know very little. Anyway, here they are. First, the one described in the passage above:

Sollinger's IAEA emblem

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. The other one had just a dove, but added another Earth:

Sollinger IAEA emblem 2

Both of which are impressively ugly compared to the actual emblem the IAEA adopted. 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.

Anyway, it’s great that they were actually found. 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. The Sollinger designs overlaid so much symbolism onto the IAEA’s emblem that the whole thing almost tipped over. For once, sending the thing to committee seems to have improved the outcome, and we got a sleek, stylish atom for the ages instead.

Visions

Firebombs, U.S.A.

Wednesday, March 12th, 2014

After the atomic bombs were dropped on Japanese cities, it didn’t take long for the US public, to start drawing what it would look like if atomic bombs went off over their own cities. PM, a New York City newspaper, may have inaugurated the genre with its August 7, 1945, issue, when it took what scant facts were known about Hiroshima and superimposed the data onto the Manhattan skyline:

PM - NYC atomic bomb - August 1945

This impulse — to see what the bomb did to others, and then to apply it to one’s own cities — worked on at least two levels. In once sense it was about making sense of the damage in intuitive terms, because maps of Hiroshima don’t make a lot of intuitive sense unless you know Hiroshima, the city. Which very few Americans would.

But it’s also a recognition that atomic bombs could possibly be dropped on the USA in the future. The atomic bomb was immediately seen as a weapon of the next war as well as the present one. It was a weapon that would, eventually, make the United States very vulnerable.

Considering how many non-atomic bombs the US dropped on Japan during the war, it’s a little interesting that nobody has spent very much time worrying about what would happen if someone firebombed the United States. Why not? Because the U.S. has never imagined that any other nation would have the kind of air superiority to pull off sustained operations like that. No, if someone was going to bomb us, it would be a one-time, brief affair.

When the US did invoke American comparisons for firebombing, it was to give a sense of scale. So the Arnold report in 1945 included this evocative diagram of Japanese cities bombed, with American cities added to give a sense of relative size:

Arnold map - Japan firebombing

So I was kind of interested to find that in the final, late-1945 issue of IMPACT, a US Army Air Forces magazine, contained a really quite remarkable map. They took the same data of the above map — the Japanese cities and their equivalent US cities — and projected them not on Japan, but on the continental United States.

It’s the only attempt I’ve seen to make a visualization that showed the damage of the ruinous American air campaign against Japan in such a vivid way:1

Click to enlarge.

Click to enlarge.

The correspondences between US and Japanese cities were chosen based on the US Census of 1940 and presumably a Japanese census from around the same period. The above map isn’t, the text emphasizes, a realistic attack scenario. Rather, it is meant to show this:

If the 69 U.S. cities on the map at right had been mattered by Jap bombers free to strike any time and anywhere in this country, you can vividly imagine the frightful impact it would have had upon our morale and war potential. Yet this is precisely what the B-29s did to Japan.

What’s remarkable is that this isn’t some kind of anti-bombing screed; it’s pro-bombing propaganda. Both of these images are bragging. The text goes on to emphasize that if someone were really targeting the US, they’d hit industrial centers like Detroit, Philadelphia, and Pittsburgh — to say nothing of Washington, DC, which is conspicuously absent and unmentioned.

IMPACT was classified “confidential” during the war, meaning it had a circulation of about 10,000 airmen. It’s a pretty wonderful read in general — it’s a vociferously pro-Air Forces rag, and is all about the importance of strategic bombing. As one might expect, it de-emphasizes the atomic bombings, in part to push back against the very public perception that we have today, where the last two major bombings are emphasized and the other 67 are forgotten. On the above maps, Hiroshima and Nagasaki are unremarkable, easily in the crowd.

I thought it would be interesting to copy out all of the data (city names, damage percentages, and look up the US Census data) and put it into an interactive visualization using a Javascript toolkit called D3. If you have a reasonably modern browser (one that supports SVG images), then check it out here:

Firebombs, USA, interactive

One thing you notice quickly when putting it this way is how large some of the metropolises were versus the relatively modest of most of the other cities. The idea of someone bombing out 55% of Sacramento, or 64% of Stockton, or 96% of Chattanooga, is kind of mind-melting. Much less to consider that a New York City minus 40% of its land area would look like.2

You can also see how cramped Japan is compared to the USA (they are at the same scale in the above image, though the projections are a bit tweaked for the layout). Even that could be more emphasized, as the text does: because Japan is so mountainous, its inhabited area is only roughly the size of Montana. So it’s even smaller than it looks.

Still, for me it’s just remarkable that this mode of visualization would be used in an official publication. These guys wanted people to understand what they had done. They wanted people to know how bad it had been for Japan. They wanted credit. And I get why — I’m not naive here. They saw it as necessary for the fighting of the war. But it also shouldn’t have been surprising, or unexpected, to those at the time that people in the future might be taken aback by the scale of the burning. Even Robert McNamara, who helped plan the firebombing operations, later came to see them as disproportionate to the US aims in the war:

This sequence, from Errol Morris’s Fog of War, has been one of my favorites for a long time. But it wasn’t until recently that I realized its source was one of these maps used for postwar boasting. It’s an incredible re-appropriation, when looked at in that light. A document meant to impress an audience, now being used to horrify a different one.

Notes
  1. Regarding the image, I scanned it out of a reprint of the IMPACT issue. Because of the crease in the center of the pages I had to do some Photoshop wizardry to make it even — so there is a lot of cleaning up around the center of the image. The data hasn’t been changed, but some of the state outlines were retouched and things like that. Similar Photoshop wizardly was also applied to the Arnold Report image to make it look clean. I suspect that the IMPACT image may have come first and the Arnold report image was derived from it, just because the IMPACT caption goes into details about methodology whereas the Arnold report does not. []
  2. But don’t confuse “destroyed” with casualties — I don’t have those numbers on hand, though if I can find them, I’ll add them to the visualization. The nice thing about D3 is that once you’ve got the basics set up, adding or tweaking the data is easy, since it is just read out of spreadsheet file. The maddening thing about D3 is that getting the basics set up is much harder than you might expect, because the documentation is really not aimed at beginners. If you are interested in a copy of the data, here is the file. []