Posts Tagged ‘Graphic design’

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. []
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. []
Visions

Death dust, 1941

Friday, March 7th, 2014

One of the biggest misconceptions that people have about the Manhattan Project is that prior to Hiroshima, all knowledge of atomic energy and nuclear fission was secret — that the very idea of nuclear weapons was unthought except inside classified circles. This is a side-effect of the narratives we tell about Manhattan Project secrecy, which emphasize how extreme and successful these restrictions on information were. The reality is, as always, more complicated, and more interesting. Fission had been discovered in 1939, chain reactions were talked about publicly a few months later, and by the early 1940s the subject of atomic power and atomic bombs had become a staple of science journalists and science fiction authors.

Campbell's magazine, Cartmill's story. Image source.

Leaks or speculation? Campbell’s magazine, Cartmill’s story. Image source.

John W. Campbell, Jr., was a prolific editor and publisher of science fiction throughout the mid-20th century. In the annals of nuclear weapons history, he is best known for publishing Cleve Cartmill’s story “Deadline” in March 1944, which talks about forming an atomic bomb from U-235. This got Cartmill and Campbell visitors from the FBI, trying to figure out whether they had access to classified information. They found nothing compromising (and, indeed, if you read Cartmill’s story, you can see that while it gets — as did many — that you can make atomic bombs from separated U-235, it doesn’t really have much truth in the specifics), but told Campbell to stop talking about atomic bombs.

But Campbell’s flirtation with the subject goes a bit deeper than that. Gene Dannen, who runs the wonderful Leo Szilard Online website, recently sent me a rare article from his personal collection. In July 1941, Campbell authored an article in PIC magazine with the provocative title, Is Death Dust America’s Secret Weapon?” It’s a story about radiological warfare in what appears to be rather middle-brow publication about entertainment. Click here to download the PDF. I don’t know anything about PIC, and haven’t been able to find much on it, but from the cover one wouldn’t necessarily expect it to be a source for people looking for hard-hitting science reporting — though the juxtaposition of DEATH DUST, “world’s strangest child,” and the “DAY DREAM” woman is a wonderfully American tableau.


PIC magazine 1941 - Campbell - Death Dust - cover

The story itself starts off with what has even by then become a clichéd way of talking about atomic energy (“A lump of U-235 the size of an ordinary pack of cigarettes would supply power enough to run the greatest bomb in the world three continuous years of unceasing flight“), other than the fact that it is one of the many publications that points out that after an exciting few years of talk about fission, by 1941 the scientists of the United States had clamped themselves up on the topic. The article itself admits none of this is really a secret, though — that all nations were interested in atomic energy to some degree. It vacillates between talking about using U-235 as a power source and using it to convert innocuous chemicals into radioactive ones.

Which is itself interesting — it doesn’t seem to be talking about fission products here, but “synthetic radium powders.” It’s a dirty bomb, but probably not that potent of one. Still, pretty exciting copy for 1941. (Campbell would much later write a book about the history of atomic energy, The Atomic Story, where he also spent a lot of time talking about “death dust.”)

The article contains a really wonderful, lurid illustration of what a city that had been sprayed with “horrible ‘death dust'” would look like:

"Even rats wouldn't survive the blue, luminescent radioactive dust. Vultures would be poisoned by their own appetites."

“Even rats wouldn’t survive the blue, luminescent radioactive dust. Vultures would be poisoned by their own appetites.”

The most interesting parts of the article are when it veers into speculation about what the United States might be doing:

With all the world seeking frantically for the secret of that irresistible weapon, what are America’s chances in the race?

It is a question of men and brains and equipment. Thanks to Hitler’s belief that those who don’t agree with him must be wrong, America now has nearly all the first-rank theoretical physicists of the world. Mussolini’s helped us somewhat, too, by exiling his best scientists. Niels Bohr, father of modern atomic theory, is at Princeton, along with Albert Einstein and others of Europe’s greatest.

The National Defense Research Committee is actively and vigorously supporting the research in atomic physics that seeks the final secrets of atomic power. Actively, because the world situation means that they must, yet reluctantly because they know better than anyone else can the full and frightful consequences of success. Dr. Vannevar Bush, Chairman of the Committee, has said: “I hope they never succeed in tapping atomic power. It will be a hell of a thing for civilization.”

Bohr was in fact still in occupied Denmark in July 1941 — he had his famous meeting with Heisenberg in September 1941 and wouldn’t be spirited out of the country until 1943. The photographs identify Harold Urey and Ernest Lawrence as American scientists who were trying to harness the power of atomic energy. Since Urey and Lawrence were, in fact, trying to do that, and since Vannevar Bush was, in fact, ostensibly in charge of the Uranium Committee work at this point, this superficially looks rather suggestive.

PIC magazine 1941 - death dust - scientists

But I think it’s just a good guess. Urey had worked on isotope separation years before fission was discovered (he got his Nobel Prize in 1934 for learning how to separate deuterium from regular hydrogen), so if you know that isotope separation is an issue, he’s your man. Lawrence was by that point known worldwide for his “atom smashing” particle accelerators, and had snagged the 1939 Nobel Prize for the work done at his Radiation Laboratory. If you were going to pick two scientists to be involved with nuclear weapons, those are the two you’d pick. As for Bush — he coordinated all of the nation’s scientific defense programs. So of course, if the US was working on atomic energy as part of their defense research, Bush would have to be in charge of it.

The other illustrations seem to be just generically chosen. They are particle accelerators of various sorts; one cyclotron and many electrostatic (e.g. Van De Graff) accelerators. Cyclotrons did have relevance to isotope separation — they were used to develop the Calutrons used at Y-12 — but the captions don’t indicate that this is why these machines are featured.

I’ve never seen any evidence that Campbell’s story in PIC came to any kind of official attention. Why not? In the summer of 1941, there was a lot of talk about U-235 and atomic energy — and Campbell’s article really isn’t the most provocative of the bunch. There wasn’t any official press secrecy of any form on the topic yet. “Voluntary censorship” of atomic energy issues, which is what would get Cartmill and Campbell in trouble later, didn’t start up until early 1943. Mid-1941 was still a time when a journalist could speculate wildly on these topics and not get visits from the FBI.

The irony is, there were official fears of a German dirty bomb, but they didn’t really crop up until 1942. But the American bomb effort was starting to get rolling in the late summer of 1941. By the end of 1941, Bush would be a convert to the idea of making the bomb and would start trying to accelerate the program greatly. It wasn’t the Manhattan Project, yet, but it was on its way. Campbell’s article was, in this sense, a bit ahead of its time.

A Campbell publication from 1947 — where he apparently has a better understanding of atomic power. Here he seems to have just scaled down a Hanford-style "pile" and added a turbine to it. It took a little more effort than that in reality...

A Campbell publication from 1947 — where he apparently has a better understanding of atomic power. Here he seems to have just scaled down a Hanford-style “pile” and added a turbine to it. It took a little more effort than that in reality…

What I find most interesting about Campbell’s article is that it reveals what the informed, amateur view of atomic energy was like in this early period. Some aspects of it are completely dead-on — that U-235 is the important isotope, that isotope separation is going to matter, that places with particle accelerators are going to play a role, that the acquisition of uranium ore was about to get important, that fears of German use of atomic energy existed. But parts of it are completely wrong — not only would dirty bombs not play a role, he doesn’t seem to understand that fission products, not irradiated substances, would play the strongest role. He doesn’t really seem to understand how nuclear power would be harnessed in a reactor. He doesn’t really seem to get fission bombs at all.

This mixture of accuracy and confusion, of guess and folly, tells us a lot about the state of public knowledge at the time. Atomic energy was a topic, it was an idea — but it wasn’t yet something tangible, a reality. So when people found out, in 1945, that the United States had made and detonated atomic fission bombs, they were primed to understand this as the beginning of a “new era,” as the realization of something they had been talking about for a long time — even if the details had been secret.

Meditations

Kilotons per kilogram

Monday, December 23rd, 2013

Nuclear weapons can be made to have pretty much as much of a bang as one wants to make them, but with increased explosive yield comes an increased weapon weight. We always talk vaguely about being able to make H-bombs to arbitrarily high yields, but recently I’ve been mulling over this fact somewhat quantitatively. I gave a talk last month at the History of Science Society Meeting on US interest in 50-100 MT bombs around the time of the Limited Test Ban Treaty, and while working on this paper I got  slightly obsessed with what is known as the yield-to-weight ratio.

Little Boy — a big bang compared to a conventional bomb, but still a very crude nuclear bomb.

Little Boy — a big bang compared to a conventional bomb, but still a very crude nuclear bomb.

What makes nuclear weapons impressive and terrible is that their default yield-to-weight ratio — that is, the amount of bang per mass, usually expressed in terms of kilotons per kilogram (kt/kg) — is much, much higher than conventional explosives. Take TNT for example. A ton of TNT weighs, well, a ton. By definition. So that’s 0.001 kilotons per 1,000 kilograms; or 0.000001 kt/kg. By comparison, even a crude weapon like the Little Boy bomb that was dropped on Hiroshima was about 15 kilotons in a 4,400 kg package: 0.003 kt/kg. That means that the Little Boy bomb had an energy density three orders of magnitude higher than a regular TNT bomb would. Now, TNT isn’t the be-all and end-all of conventional explosives, but no conventional explosive gets that much boom for its buck compared to a nuke.

The Little Boy yield is much lower than the hypothetical energy density of uranium-235. For every kilogram of uranium-235 that completely fissions, it releases about 17 kt/kg. That means that less than a kilogram of uranium-235 fissioned in the Little Boy bomb to release its 15 kilotons of energy. Knowing that there was 64 kg of uranium in the bomb, that means that something like 1.3% of the uranium in the weapon actually underwent fission. So right off the bat, one could intuit that this is something that could probably be improved upon.

Fat Man — a lot better use of fissile material than Little Boy, but no more efficient in terms of yield-to-weight.

Fat Man — a lot better use of fissile material than Little Boy, but no more efficient in terms of yield-to-weight.

The Fat Man bomb had a much better use of fissile material than Little Boy. Its yield wasn’t that much better (around 20 kilotons), but it managed to squeeze that (literally) out of only 6.2 kilograms of plutonium-239. Pu-239 releases around 19 kilotons per kilogram that completely fissions, so that means that around 15% of the Fat Man core (a little under 1 kg of plutonium) underwent fission. But the bomb itself still weighed 4,700 kg, making its yield-to-weight ratio a mere 0.004 kt/kg. Why, despite the improve efficiency and more advanced design of Fat Man, was the yield ratio almost identical to Little Boy? Because in order to get that 1 kg of fissioning, it required a very heavy apparatus. The explosive lenses weighed something like 2,400 kilograms just by themselves. The depleted uranium tamper that held the core together and reflected neutrons added another 120 kilograms.  The aluminum sphere that held the whole apparatus together weighed 520 kilograms. The ballistic case (a necessary thing for any actual weapon!) weighed another 1,400 kg or so. All of these things were necessary to make the bomb either work, or be a droppable bomb.

So it’s unsurprising to learn that improving yield-to-weight ratios was a high order of business in the postwar nuclear program. Thermonuclear fusion ups the ante quite a bit. Lithium-deuteride (LiD), the most common and usable fusion fuel, yields 50 kilotons for every kilogram that undergoes fusion — so fusion is nearly 3 times more energetic per weight than fission. So the more fusion you add to a weapon, the better the yield-to-weight ratio, excepting for the fact that all fusion weapons require a fission primary and usually also have very heavy tampers.

I took all of the reported American nuclear weapon weights and yields from Carey Sublette’s always-useful website, put them into the statistical analysis program R, and created this semi-crazy-looking graph of American yield-to-weight ratios:

Yield-to-weight ratios of US nuclear weapons

The horizontal (x) axis is the yield in kilotons (on a logarithmic scale), the vertical (y) axis is the weight in kilograms (also on a log scale). In choosing which of the weights and yields to use, I’ve always picked the lowest listed weights and the highest listed yields — because I’m interested in the optimal state of the art. The individual scatter points represent models of weapons. The size of each point represents how many of them were produced; the color of them represents when they were first deployed. Those with crosses over them are still in the stockpile. The diagonal lines indicate specific yield-to-weight ratio regions.

A few points of interest here. You can see Little Boy (Mk-1), Fat Man (Mk-3), and the postwar Fat Man improvements (Mk-4 — same weight, bigger yield) at the upper left, between 0.01 kt/kg and 0.001 kt/kg. This is a nice benchmark for fairly inefficient fission weapons. At upper right, you can see the cluster of the first H-bomb designs (TX-16, EC-17, Mk-17, EC-24, Mk-24) — high yield (hence far to the right), but very heavy (hence very high). Again, a good benchmark for first generation high-yield thermonuclear weapons.

What a chart like this lets you do, then, is start to think in a really visual and somewhat quantitative way about the sophistication of late nuclear weapon designs. You can see quite readily, for example, that radical reductions in weight, like the sort required to make small tactical nuclear weapons, generally results in a real decrease in efficiency. Those are the weapons in the lower left corner, pretty much the only weapons in the Little Boy/Fat Man efficiency range (or worse). One can also see that there are a few general trends in design development over time if one looks at how the colors trend.

First there is a movement down and to the right (less weight, more yield — improved fission bombs); there is also a movement sharply up and to the right (high weight, very high yield — thermonuclear weapons) which then moves down and to the left again (high yield, lower weight — improved thermonuclear weapons). There is also the splinter of low-weight, low-yield tactical weapons as well that jots off to the lower left. In the middle-right is what appears to be a sophisticated “sweet spot,” the place where all US weapons currently in the stockpile end up, in the 0.1-3 kt/kg range, especially the 2-3 kt/kg range:

Yield-to-weight ratios -- trends

These are the bombs like the W-76 or the B-61 — bombs with “medium” yield warheads (100s rather than 1,000s of kilotons) in relatively low weight packages (100s rather than 1000s of kilograms). These are the weapons take advantage of the fact that they are expected to be relatively accurate (and thus don’t need to be in the multi-megaton range to have strategic implications), along with what are apparently sophisticated thermonuclear design tricks (like spherical secondaries) to squeeze a lot of energy out of what is a relatively small amount of material. Take the W-76 for example: its manages to get 100 kilotons of yield out of 164 kilograms. If we assume that it is a 50/50 fission to fusion ratio, that means that it manages to fully fission about 5 kilograms of fissionable material, and to fully fuse about 2 kilograms of fusionable material. And it takes just 157 kg of other apparatus (and unfissioned or unfused material) to produce that result — which is just a little more than Shaquille O’Neal weighs.

Such weapons aren’t the most efficient. Weapon designer Theodore Taylor wrote in 1987 that 6 kiloton/kilogram had been pretty much the upper limit of what had even been achieved.1 Only a handful of weapons got close to that. The most efficient weapon in the US stockpile was the Mk-41, a ridiculously high yield weapon (25 megatons) that made up for its weight with a lot of fusion energy.

The components of the B-61 nuclear weapon — the warhead is the bullet-shape in the mid-left. The B-61 was designed for flexibility, not miniaturization, but it's still impressive that it could get 20X the Hiroshima bomb's output out of that garbage-can sized warhead.

The components of the B-61 nuclear weapon — the warhead is the bullet-shape in the mid-left. The B-61 was designed for flexibility, not miniaturization, but it’s still impressive that it could get 20X the Hiroshima bomb’s output out of that garbage-can sized warhead.

But given that high efficiency is tied to high yields — and relatively high weights — it’s clear that the innovations that allowed for the placing of warheads on MIRVed, submarine-launched platforms are still pretty impressive. The really magical range seems to be for weapons that in the hundred kiloton range (more than 100 kilotons but under a megaton), yet under 1,000 kilograms. Every one of those dates from after 1962, and probably involves the real breakthroughs in warhead design that were first used with the Operation Dominic  test series (1962). This is the kind of strategic miniaturization that makes war planners happy.

What’s the payoff of thinking about these kinds of numbers? One is that it allows you to see where innovations have been made, even if you know nothing about how the weapon works. In other words, yield-to-weight ratios can provide a heuristic for making sense of nuclear design sophistication, comparing developments over time without caring about the guts of the weapon itself. It also allows you to make cross-national comparisons in the same fashion. The French nuclear arsenal apparently developed weapons in that same miniaturized yield-to-weight range of the United States by the 1970s — apparently with some help from the United States — and so we can probably assume that they know whatever the United States figured out about miniaturized H-bomb design in the 1960s.

The Tsar Bomba: a whole lot of boom, but a whole lot of weight. The US thought they could make the same amount of boom for half the weight.

The Tsar Bomba: a whole lot of boom, but a whole lot of weight. The US thought they could make the same amount of boom for half the weight.

Or, to take another tack, and returning to the initial impetus for me looking at this topic, we know that the famous “Tsar Bomba” of the Soviet Union weighed 27,000 kilograms and had a maximum yield of 100 Mt, giving it a yield-to-weight ratio of “only” 3.43 kilotons/kilograms. That’s pretty high, but not for a weapon that used so much fusion energy. It was clear to the Atomic Energy Commission that the Soviets had just scaled up a traditional H-bomb design and had not developed any new tricks. By contrast, the US was confident in 1961 that they could make a 100 Mt weapon that weighed around 13,600 kg (30,000 lb) — an impressive 7.35 kiloton/kilogram ratio, something well above the 6 kt/kg achieved maximum. By 1962, after the Dominic series, they thought they might be able to pull off 50 Mt in only a 4,500 kg (10,000 lb) package — a kind of ridiculous 11 kt/kg ratio. (In this estimate, they noted that the weapon might have an impractically large diameter as a result, perhaps because the secondary was spherical as opposed to cylindrical.) So we can see, without really knowing much about the US had in mind, that it was planning something very, very different from what the Soviets set off.

It’s this black box approach that I find so interesting about these ratios. It’s a crude tool, to be sure, but a tool nonetheless. By looking at the broad trends, we get insights into the specifics, and peel back the veil just a tiny bit.

Notes
  1. Theodore B. Taylor, “Third Generation Nuclear Weapons,” Scientific American 256, No. 4 (April 1987), 30-39, on 34: “The yield-to-weight ratios of pure fission warheads have ranged from a low of about .0005 kiloton per kilogram to a high of about .1 kiloton per kilogram. [...] The overall yield-to-weight ratio of strategic thermonuclear warheads has been as high as about six kilotons per kilogram. Although the maximum theoretical ratios are 17 and 50 kilotons per kilogram respectively for fission and fusion reactions, the maximum yield-to-weight ratio for U.S. weapons has probably come close to the practical limit owing to various unavoidable inefficiencies in nuclear weapon design (primarily arising from the fact that it is impossible to keep the weapon from disintegrating before complete fission or fusion of the nuclear explosive has taken place.” []