Redactions

The Fat Man’s uranium

by Alex Wellerstein, published November 10th, 2014

What a long set of weeks it has been! On top of my usual teaching load (a few hours of lecture per week, grading, etc.), I have given two public talks and then flown to Chicago and back for the annual History of Science Society meeting. So I’ve gotten behind on the blog posting, though I have more content than usual for the next few weeks built up in my drafts folder, without time for me to finish it up. During this busy time, by complete coincidence, I also got briefly interviewed for both The Atlantic (on plutonium and nuclear waste) and The New York Times (on the apparent virality of nuclear weapons history).

Louis Slotin and Herb Lehr at the assembly of the Trinity "Gadget." Source: Los Alamos National Laboratory Archives, photo TR-229.

Louis Slotin and Herb Lehr at the assembly of the Trinity “Gadget.” Source: Los Alamos National Laboratory Archives, photo TR-229.

The Times article had a phrase in it that has generated a few e-mails to me from a confused reader, so I thought it was worth clarifying on here, because it is actually an interesting detail. It is one of those funny phrases that if you knew nothing about the bomb you’d never notice it, and if you knew a good deal about the bomb you’d think it was wrong, but if you know a whole lot more than most people care to know unless they are serious bomb nerds you actually see that it is correct.

Here’s the quote:

First, he glanced at the scientists assembling what they called “the gadget,” a spherical test device five feet in diameter. Then, atop a wooden crate nearby, he noticed a small, blocky object, nondescript except for the role he suddenly realized it played: It was a uranium slug that held the bomb’s fuel. In July 1945, its detonation lit up the New Mexican desert and sent out shock waves that begot a new era.

I’ve added emphasis to the part that may seem confusing. The Trinity “Gadget” and the Fat Man bomb, as everyone knows, were fueled by fission reactions in a sphere of plutonium. The Little Boy bomb dropped on Hiroshima, by contrast, was fueled by enriched uranium. So what’s this reference to a uranium slug inside the Trinity Gadget? Isn’t that wrong?

Detail from the above photo showing the tamper plug cylinder. Inset is a rare glimpse of what the tamper probably looked like, taken from a different Los Alamos photo related to Slotin's criticality accident. (It is in the middle-right of the linked photo. Yes, I cop to spending time searching the edges of photos like this for interesting things...) You can see how the tamper plug, rotated, would be inserted into the middle of the tamper sphere.

Detail from the above photo showing the tamper plug cylinder. Inset is a rare glimpse of what the tamper probably looked like, taken from a different Los Alamos photo related to Slotin’s criticality accident. (It is in the middle-right of the linked photo. Yes, I cop to spending time searching the edges of photos like this…) You can see how the tamper plug, rotated, would be inserted into the middle of the tamper sphere.

Perhaps surprisingly — no, it’s not. There was uranium inside both the “Gadget” and Fat Man devices — in the tamper. The tamper was a sphere of uranium that encased the plutonium pit, which itself encased a polonium-beryllium neutron source, Russian-doll style. Here uranium was chosen primarily for its physical rather than its nuclear properties: it was natural, unenriched uranium (“Tuballoy,” in the security jargon of the time), and its purpose was to hold together the core while the core did its best to try and explode. (It also helped reflect neutrons back into the core, which also worked to improve the efficiency.)

The inside of an exploding fission bomb can be considered as a race between two different processes. One is the fission reaction itself, which, as it progresses, rapidly heats the core. This heating of the core, however, causes the core to rapidly expand — the core is trying to blow itself apart. If the core expands beyond a certain radius, the fission chain reaction stops, because the fission neutrons won’t find further plutonium nuclei to react with. If you are a bomb designer, and want your bomb to have a pretty big boom, you want to hold the bomb core together as long as possible, because every 10 nanoseconds or so you can hold it together equals another generation of fission reactions, and each generation releases exponentially more energy than the previous.

An image that somewhat evokes how bomb designers talk about the dueling conditions inside of the bomb, when they are talking to each other. The "snowplow region" is where the expanding bomb core runs into the tamper and is compressing it from the inside. This is a level of bomb design that I would have normally assumed would be classified but it has been very clearly declassified here, so I guess not. From Glasstone, "Weapons Activities of Los Alamos, Part I" (see footnotes).

An image that somewhat evokes how bomb designers talk about the dueling conditions inside of the bomb, when they are talking to each other. The “snowplow region” is where the expanding bomb core runs into the tamper and is compressing it from the inside. This is a level of bomb design that I would have normally assumed would be classified but it has been very clearly declassified here, so I guess not. From Glasstone, “Weapons Activities of Los Alamos, Part I” (see footnotes).

So in the Fat Man and Trinity bombs, this is accomplished with a heavy sphere of natural uranium metal. Uranium is heavy and dense, and the process of making plutonium and enriched uranium required the United States to stockpile thousands of tons of it, so the relatively small amount needed for a tamper was easily at-hand. It makes a good substance with which to try and hold an exploding atomic bomb together. The Little Boy bomb, as an aside, used a tungsten tamper, for some reason (maybe to avoid excessive background neutrons, I don’t know).

Now to add one more little bit of detail: we tend to think of the Trinity/Fat Man implosion bombs as just being a set of spheres-inside-spheres. This is a convenient simplification of the actual geometry, which had other factors that influenced it. The tamper, for example, was not just two halves of a hollow sphere that could fit together. Rather, it was more like a solid sphere out of which a central cylinder had been removed. The cylinder was known as the “tamper plug,” and was itself made of two halves that, when assembled, had room for the plutonium pit inside of them.

Why do it this way? Because the scientists and engineers wanted to be able to insert the fissile pit portion into the bomb as one of the final additions. This makes good sense from a safety point of view — they wanted it to be relatively easy to add the final, “nuclear” component of the bomb and to keep it separate from the non-nuclear components (like the high explosives) as long as possible. I don’t want to over-emphasize the “ease” of this operation, because it was not a quick, last-minute action to put the pit inside the bomb. (Some later bomb designs which featured in-flight core insertion were designed to be just this, but this was some years away.) It was still a tetchy, careful operation. But they could assemble the entire rest of the tamper, pusher, and high explosives, then remove one layer of high explosives, remove the top of the pusher, and then lower the tamper plug (with pit) into the center, then replace all of the other parts, hook up the detonators and electrical system, and so on.

A rendering I made in Blender to illustrate the principle here. The pit and initiator are inside of the plug (expanded at right), which is then sealed into a cylinder and inserted into the tamper sphere at the center of the bomb. The tamper is itself embedded in a boron shell which is inside of an aluminum shell which is inside of the explosive lenses which is inside of the casing. This is part of a modeling/visualizing project I've been working on for a little while now and will post more on at a future date. 

A rendering I made in Blender to illustrate the principle here. The pit and initiator are inside of the plug (expanded at right), which is then sealed into a cylinder and inserted into the tamper sphere at the center of the bomb. The tamper is itself embedded in a boron shell which is inside of an aluminum shell which is inside of the explosive lenses which is inside of the casing. This is part of a modeling/visualizing project I’ve been working on for a little while now and will post more on at a future date. The dimensions are roughly correct though there are still many simplified detail (e.g. exactly how the plug fits together — there were uranium screws!).

So when John Coster-Mullen describes, as in the previously-quoted New York Times article, finding a picture of the tamper plug, it’s kind of a cool thing. There’s only one picture that shows it (the one at the beginning of this post), and it is one of those things that you don’t even usually notice about that picture until someone points it out to you. I never noticed it until John pointed it out for me, even though I’d seen the picture many times before. Usually one’s attention is drawn to the Gadget sphere itself, and the people standing around (including Louis Slotin, who would later be killed by playing with a core). It’s kind of surprising it was declassified, since the length of the tamper plug is the diameter of the tamper, and the width of the plug is just a little bigger than the diameter of the plutonium core. The US government usually doesn’t like to reveal, even inadvertently, those kinds of numbers.

There is also one little fact about the natural uranium in the Gadget and Fat Man bomb that is not well appreciated, and I didn’t appreciate well until reading John’s book. (Which I have heard people say is rather expensive for a self-published production, but if you’re a serious Manhattan Project geek it is hard to imagine how you’d get by without a copy of it — it is dense with technical details and anecdotes. It is one of the only books that I don’t often bother to put back in the bookcase because I end up needing to reference it every week or so.)

Neutron cross-sections for the fissioning of uranium and plutonium. The higher the cross-section, the more likely that fission will occur. (Not shown on here is the competing capture cross-section, which matters a lot for U-238.) The indicated "fission neutron energy" means that that is the approximate energy level of neutrons released from fission reactions. So you can see why, in a reactor, those are slowed down by the moderator to increase the likelihood of fissioning. In a bomb, there is no time for slowing things down, so you need much more fissile material in much higher concentrations. Source: World Nuclear Association.

Neutron cross-sections for the fissioning of uranium and plutonium. The higher the cross-section, the more likely that fission will occur. The indicated “fission neutron energy” means that that is the approximate energy level of neutrons released from fission reactions. So you can see why, in a reactor, those are slowed down by the moderator to increase the likelihood of fissioning. In a bomb, there is no time for slowing things down, so you need fissile material in much higher concentrations. Source: World Nuclear Association.

In talking about which elements are fissile — that is, can sustain a nuclear fission chain reaction — technical people tend to talk about neutron cross sections. This just means, in essence, that the likelihood of a giving elemental isotope (e.g. uranium-235, plutonium-239) undergoing fission when encountering a neutron is related to the energy of that neutron. At the size of neutrons, energy, speed, and temperature all considered to be the same thing. If you look at a neutron cross section chart, like the one above, you will see that uranium-235 has a high likelihood of fissioning from slow neutrons, and a low-but-not-zero likelihood of fissioning from faster neutrons. You will also see that the neutrons released by fission reactions are pretty fast. This is why to sustain a chain reaction in uranium you either need to slow the neutrons down (like in a nuclear reactor, which uses a moderator to do this), or pack in so many U-235 atoms that even the low probability of fissioning from fast neutrons doesn’t mean that a chain reaction won’t happen (like in a nuclear bomb, where you enrich the uranium to be mostly U-235).

Still with me? If you look a little further on the graph, you’ll see that uranium-238 also has a possibility of fissioning, but it is a pretty low one and only even becomes possible with pretty fast neutrons. This is why, in a nutshell, that unenriched uranium can’t power an atomic bomb by itself: it is fissionable but not fissile, because it can’t reliably take fission neutrons and turn them into further fission reactions. But people who have studied how thermonuclear weapons are used know that even uranium-238 can contribute a lot of explosive energy, if it is in the presence of a lot of high-energy neutrons. In a multistage hydrogen bomb, at least 50% of the final explosive energy is derived from the fissioning of U-238, which is made possible by the high-energy neutrons produced from the nuclear fusion stage of the bomb (which itself is set off by an initial fission stage). The neutrons produced by deuterium-tritium fusion are around 14 times more energetic than fission neutrons, so that lets them fission U-238 easily. From the cross-section chart above, you can see that U-238 fissioning can happen from fission neutrons, but only if they happen to be pretty high energy to begin with and stay that way. In practice, neutrons lose energy rather quickly. Still, according to a rather sophisticated analysis of the glassified remains of the Trinity test (“Trinitite”) done a few years back by the scientistsThomas M. Semkow, Pravin P. Parekh, and Douglas K. Haines, a significant portion of the final fissioning output at Trinity (and presumably also Nagasaki) came from the fast fissioning of the tamper, with some of that energy released from the U-238 fissioning.

For the hardcore bomb geeks, here is a sort of "conclusion table" from the Semkow et al. article. Note that they calculate at least 30% fissioning from uranium, and give some indication the amount of compression of the core, the number of neutrons created, and so on.

For the hardcore bomb geeks, here is a sort of “conclusion table” from the Semkow et al. article. Note that they calculate at least 30% fissioning from uranium, and give some indication the amount of compression of the core, the number of neutrons created, and so on. Their terminology of the “eyeball” is taken from Richard Rhodes, who uses the term in passing in The Making of the Atomic Bomb, and refers to the confined area where the fission chain reaction is taking place.

How significant? Semkow et al. calculate that about 30% of the total yield of the Trinity test came from fissioning of the uranium tamper, which translates to about 6 kilotons of energy. If they had made the tamper out of tungsten (as was the Little Boy tamper), then the total yield of the Gadget would have only been around 14-15 kilotons — not that different from Little Boy (which was ~13-15 kt). And presumably if the Little Boy bomb had used a uranium tamper, assuming that didn’t cause problems with the design (which it probably would have, otherwise they probably would have used one), it would have had the same yield. (This doesn’t mean that Little Boy wasn’t, in fact, horribly inefficient — it got about the same yield but it required 10X the fissile the material to do so!) The total mass of the tamper was around 120 kg of natural uranium, so if it contributed 6 kilotons of yield that means around 350 grams of the tamper underwent fission, and that is about 0.3% of the total mass.

So the fact that Trinity and Fat Man had uranium inside of them is already kind of interesting, but the fact that a large portion of the blast derived from that uranium is sort of a neat detail. Why don’t we generally learn about this? It isn’t that it is so terribly classified, per se, but it does require a lot of detailed explanation, as evidenced by the length of this post. We tend to abstract the mechanics of the bombs for explaining their conceptual role, and explaining the basic concepts of how they work. I have no problem with this, personally, because hey, let’s be honest, the exact amount of energy derived from different types of fissioning in the bombs is a pretty wonky thing to care about! But every once in awhile you need to understand the wonky things if you want to talk about, say, what that funny little “plug” is in the top-most photograph, and its role in the bomb. I suppose one of the points of the phenomena described by the Times article, where the geek population on the Internet is providing a newfound audience to Manhattan Project details, is that these sorts of wonky aspects are no longer limited to people like John Coster-Mullen, Carey Sublette, or myself. There are some people who might see this focusing on the technical details as missing the broader picture. I don’t happen to think that myself — much of the broader picture is in fact embedded in the technical details, and “new” discussions of technical details are one way of shaking people out of the calcified narratives of the Manhattan Project, something which, as we approach the 70th anniversary of Hiroshima and Nagasaki, seems to me a valuable endeavor.

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Meditations

The riddle of Julius Rosenberg

by Alex Wellerstein, published October 17th, 2014

David Greenglass, the key witness in the espionage case of Julius and Ethel Rosenberg, has died. He was Ethel Rosenberg’s brother, and his testimony doomed both his sister and brother-in-law. Greenglass explained to the jury how he had, as an engineer at Los Alamos, been drawn into a Soviet spy ring by his brother, and argued that his sister played a non-trivial role in the entire affair. Greenglass also provided, with the sanction of the Atomic Energy Commission’s classification officer, the first public description of an implosion nuclear weapon. Exhibit 8, drawn in Greenglass’ hand, was proclaimed by the prosecution to be a “sketch of the very atomic bomb itself,” and could not be countered by the Rosenbergs’ attorney. Instead, the defense argued that releasing such a sketch into the world was a security risk (even though, again, it had been pre-approved for release), and they had it impounded, where it stayed out of view until the late 1970s. Nevertheless, Greenglass’ description of the bomb quickly entered into the public eye, and “implosion” became part of our nuclear lexicon.

greenglass-secret-of-the-atomic-bomb

(Exhibit 8 was later released, in the 1970s, for reexamination as part of a hearing on behalf of Morton Sobell, another defendant at the Rosenberg trial. The physicist Phillip Morrison argued that it was a crude, child-like sketch of the bomb, and of little value to the Soviets. The judge concluded, however, that the basic principle of implosion was still revealed by the drawing, and it was still classified. At the very least, it helped to confirm other espionage data as legitimate. The New York NARA office scanned the above version of it for me.)

Greenglass later admitted to have perjured himself. The deal was that he would implicate Ethel, and in exchange, his wife, Ruth Greenglass, would walk free. Greenglass took the deal — he didn’t want to leave his children unwatched, even while he himself went to prison. And perhaps he felt a tinge of frustration that Julius and Ethel wouldn’t cooperate like he had. Asked about it years later, he said: “My wife is more important to me than my sister. Or my mother or my father, O.K.? And she was the mother of my children.”

David Greenglass (in glasses), conducting some sort of testimony or press conference. Harry Gold is two seats to his right. Source: Google LIFE images.

David Greenglass (in glasses), conducting some sort of testimony or press conference. Harry Gold is two seats to his right. Source: Google LIFE images.

The rules of American Cold War prosecutions, and persecutions, were pretty simple. First, admit that you had done whatever it was you had done. In the case of people accused of being Communists, it meant admitting you had been a member of the Communist Party. In the case of spies, it meant admitting you were a spy. Second, give up the names of your contacts and associates, so that they could then be prosecuted/persecuted. In this way, searches for spies and Communists was something of a security-tinged pyramid scheme, an endless engine for new sources.

What if you hadn’t done what you were accused of? Or wouldn’t confess, even if you had done it? Well, that’s the tricky case, isn’t it? The place where the system breaks down, where there real violence gets done.

In the case of the Rosenbergs, the FBI had pretty good evidence of Julius’ guilt. Not only did they have the confessions of Greenglass and Harry Gold, the “courier” for the spy ring, but they — unbeknownst to almost all at the time — also had the evidence gleaned from the VENONA intercepts, where Soviet communications during World War II had been secretly decrypted. The combination of VENONA and the confessions makes the case against Julius Rosenberg pretty much a slam dunk. Since the revelation of VENONA in the 1990s, I have not yet met a historian who doesn’t think that Julius was a spy. Because VENONA was secret, however, the FBI could not introduce the evidence into court (and secret testimony in criminal cases is generally a “no-no” under American jurisprudence), and so had to rely on the testimony of Greenglass and Gold to make the case, which made it look like a lot less obvious at the time, because both were not extremely reliable witnesses (Gold was a strange supplicant who would say almost anything; Greenglass was angling for a deal and indeed, did perjure himself).

Mugshots of Julius and Ethel Rosenberg. Source: Library of Congress.

Mugshots of Julius and Ethel Rosenberg. What is going on in Julius’ mind? Source: Library of Congress.

Ethel was much more problematic. What she knew, or didn’t know, about the spy operation isn’t as clear. Julius got code-names in the VENONA transcripts (“Antenna” and “Liberal”), which indicate he was something of a key asset. Ethel’s code-name was… “Ethel,” indicating she was not. Did she know what Julius and her brother were up to? It seems hard to imagine she did not. Did she deserve the electric chair? Maybe, maybe not. I happen to be on the side that thinks that capital punishment for an espionage crime committed in the service of a state that was then an ally is extreme. Much less for someone whose role, like Ethel’s, was probably fairly minor. It is clear, from the historical record, that pushing for the death penalty for both was part of a strategy to scare the two into cooperating, and to scare others who dared not to cooperate. I don’t think executing them achieved anything like justice.

But I have some real problems feeling sympathy and empathy for the Rosenbergs. They maintained their absolute innocence all the way through their executions. They left two children as orphans. They created fissures in American politics that still resonate to this day, with Cold War liberals absolutely convinced of their innocence, and Cold War hawks convinced of their being traitors. The by-product was an ugly polarization of American Cold War politics that was potentially avoidable. Now we know that at least Julius was guilty, and that he lied to everyone, repeatedly. He had the choice to avoid the chair. He chose to be a martyr. And, again, to orphan his children.

"Ethel and Julius Rosenberg’s sons, Robert, 6, left, and Michael, 10, looking at a 1953 newspaper. They still believe their parents did not deserve to die." Photo from the Associated Press, via the New York TImes

“Ethel and Julius Rosenberg’s sons, Robert, 6, left, and Michael, 10, looking at a 1953 newspaper.” Photo from the Associated Press, via the New York TImes

I find that hard to respect. Who was he protecting? Stalin? The Communist Party? His reputation? It is hard to conceive what cause would be worth what he did. It is one thing to doom himself, but another to doom his wife. And I keep coming back to the children. Who would do that to their children? Both of the children were, until relatively recently, defenders of the innocence of their parents, which makes perfect sense. What a crushing blow to believe the contrary.

Part of the problem, from a latter-day point of view, is that Julius Rosenberg, by the very nature of his lack of confession, is a Sphinx. On his motivations and justifications, he is silent — he never told his side of the story, the real, non-B.S. side of the story. It makes him feel cold to me, gazing out from those pictures. I find myself saying: “Why’d you do it?” We know he spied. If he had just told us why, maybe we could understand, and have some empathy. But he took his side of the story to his grave.

It is a very different situation than with Klaus Fuchs, Theodore Hall, Harry Gold, and even David Greenglass. Fuchs confessed at length about his motivations, his feelings on the subject. He felt the Soviets were owed the information, as those who were bleeding the most during the war against Fascism. Hall was very young at the time of his espionage, but one can recognize and sympathize with the naive politics of youth. And Hall’s central belief, that maybe the world would be safer without just one country having atomic weapons, is not actually a totally naive position — it is the essence of deterrence theory, for better or worse. Gold’s way into espionage was not ideological, but psychological: he was a needy person and fell in with the wrong crowd, who exploited his near-pathological desire to please. (When he was caught by the FBI, they exploited this as well in turning him into a key witness.)

"Six Principals in the Russian Atomic Spy Ring," New York Times, April 1, 1951.

“Six Principals in the Russian Atomic Spy Ring,” New York Times, April 1, 1951, page 10E.

What if Julius had left a last testament? A confession to be released years later? How would that change the story? What if he pled with us to understand his position? I can completely understand why someone would spy for the Soviets during World War II. The Communists appeared to many to be the only real power willing to fight Fascism, racism, and economic injustice. Was it a big sham? Of course. Stalin was no freedom fighter. The American Communist Party was opportunistic and crass regarding its cause célèbres. But one can at least empathize with the position: you can see the world through their eyes, at that terrible time, and conclude that cutting the Soviets out of the atomic bomb project was a form of injustice.

But can I find a way to understand the silence of Julius Rosenberg? Why he doomed himself and his wife to death? Why he doomed his children to orphanhood? This I struggle with. What could be worth all that? Who, or what, was he saving? It is hard for me to imagine anything worth that. To me, this is much worse, from a human standpoint, than the spying. Spying makes sense to me. It happens all the time. But lying in such a self-destructive way, for seemingly no purpose? This makes no sense.

And so Julius Rosenberg brings a bad taste in my mouth. As a historian, this is not a great thing: one wants to be as objective and neutral as possible with regards to one’s historical actors. One doesn’t want to develop personal animosities, even for terrible people, because it can color your viewing of the past. I don’t think I would be able to be wholly neutral with regard to Julius. Fortunately, he comes into my research only glancingly (I am not interested in him, per se, but I am interested in how the AEC, FBI, etc. handled the trial). If only he had told us what he felt, why he did what he did! Even if it was stupid, even if it was naive, even if it was pathetic — it would be something to go on, something to feel for, something to make a connection to.

Greenglass’s choice of his wife and children over his sister and brother-in-law is an agonizing one. One can hardly fault him for choosing the path he did. Especially since, if Julius had confessed to what we now know for sure that he did, nobody would have been executed. I find myself pitying David Greenglass. He made some bad decisions, and paid a very steep price for them. I have a harder time finding similar pity, or sympathy, for his brother-in-law, Julius, whose historical silence is deafening.

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News and Notes

Public lecture: “The Secret Histories of Laser Fusion”

by Alex Wellerstein, published October 16th, 2014

Sorry for the radio silence last week! A lot has been going on over here. More on all that pretty soon. Tomorrow morning I will be putting up a post on the death of David Greenglass.

I wanted to let people in the greater New York City metro area know about a public lecture I am giving on Wednesday, October 29, 2014, as part of the New York City History of Science Society Consortium, at Columbia University.

Meeting of the New York City History of Science Society Consortium

Wednesday, October 29th, 2014, 6:00-7:30 PM

Faculty House, Columbia University, 64 Morningside Drive

Wellerstein - Laser fusion talk

“Clean, Limitless, Classified: The Secret Histories of Laser Fusion”

Alex Wellerstein, Stevens Institute of Technology

The invention of the laser and its proliferation in scientific settings created a unique problem for the United States government starting in the 1960s. The Cold War regime of nuclear secrecy had required an absolute legal distinction between “peaceful” civilian technology and “dangerous” military technology: the former needing wide dissemination and development by the private sector, the latter being tightly regulated under penalty of imprisonment and death. But the emergent technology of laser fusion began to challenge and blur these Cold War categories. For its proponents, which included both international scientists and private entrepreneurs, laser fusion held out the hope of clean, limitless power generation during a time of increasing energy instability. But at its heart was a form of physics that was, for government censors, far too near to the methods used in the design of advanced thermonuclear weapons. This talk will use newly declassified files to tell the international history of laser fusion in the 1960s and 1970s as a case study for looking at the unusual classification problems of late Cold War nuclear technology. 

This is a very fun talk, one I’ve been working on (and workshopping on) for a few years now. It is based on interviews with some of the pioneers of laser fusion technology, and a whole lot of documents I got declassified by the Department of Energy relating to the declassification of laser fusion technology in the 1970s, the KMS Fusion affair, and international development of inertial confinement fusion. In a world where some new fusion hype seems to be bursting out (or petering out) on a weekly basis, this is a history with more relevance than ever, and has some moments in it that are sure to shock and delight. For those who are more interested in the weapons side of the nuclear picture, there’s a lot going on related to that in this as well, in describing the back-and-forth between the work of H-bomb designs and the work on “civilian” applications, and the complete mess that this put the Atomic Energy Commission in as they tried to figure out their classification policies and priorities. There’s a lot going on in this one.

All are welcome — there doesn’t seem to be a need to RSVP. I don’t know if it is being recorded. I don’t think it is being streamed.

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Visions

The lost IAEA logo

by Alex Wellerstein, published 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.

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Posted in Visions | 7 Comments »

Meditations

Tokyo vs. Hiroshima

by Alex Wellerstein, published September 22nd, 2014

How many people would have died if an atomic bomb had been dropped on Tokyo in early 1945, instead of firebombs? Before you accuse me of excessive obsession with morbidity (as one anonymous e-mailer recently did), let me explain to you how I came to ask myself this question, and what the consequences of the answer are.

Before the dropping of the atomic bomb on Hiroshima and Nagasaki, there was the burning of Tokyo. Operation Meetinghouse, the early March 1945 raid on Tokyo that involved over 330 B-29s dropping incendiary bombs from low-altitude at night, killed roughly 100,000 people, and may have injured and made homeless an order of magnitude more. As with all statistics on the damage caused by strategic bombing during World War II, there are debatable points and methodologies, but most people accept that the bombing of Tokyo probably had at least as many deaths as the Hiroshima bombing raid, and probably more. It is sometimes listed as the most single deadly air raid of all time as a consequence.

The ruins of 1945: Tokyo, left, and Hiroshima, right.

The ruins of 1945: Tokyo, left, and Hiroshima, right.

So it is understandable that many people, including myself, point to Tokyo whenever people want to talk about Hiroshima and Nagasaki. You can’t see the atomic bombings in isolation. The practice of targeting civilian areas with massively destructive aerial bombing had already been done before. And to some, the atomic bombs were just a refinement of the art of area bombing — a more efficient means to accomplish the same ends.

However, there are a few points that I fear get missed in that kind of equivalence. I certainly agree that the philosophy of bombing used at Hiroshima and Nagasaki wasn’t a new one. Indeed, the experience of firebombing gave a lot of guidance to the question of nuclear targeting. The goals were similar, though the people planning the atomic bombs emphasized the raw terror that they hoped such a spectacle would inspire.

But I depart from the standard comparison in two places. The first is the idea that since the atomic bombings were not original in targeting civilians, then they do not present a moral or ethical question. As I’ve written about before, I think the question of morality gets more problematic. If the atomic bombings were one-off events, rare interventions to end the war, then it might (for some) be compelling to say that they were worth the price of crossing over some kind of line regarding the deliberate burning of civilians to death en masse. But if they were instead the continuation of a well-established policy of burning civilians to death en masse, then the moral question gets much broader. The question changes from, Was it morally justified to commit a civilian massacre two times?, to Was it morally justified to make civilian massacre a standard means of fighting the war? 

I want to state explicitly that I don’t think, and I don’t want my phrasing to imply, that the answer to the above is necessarily an unequivocal “no.” There are certainly many moral frameworks that can allow for massacres (e.g. ends-justify-the-means). But I prefer to not dress this sort of thing up in euphemisms, whether we think it justified or not.  Massacre means to deliberately and indiscriminately kill people. That is what you get when you bomb densely-populated cities with weapons that cannot distinguish between civilians and members of the military. Incendiary raids and atomic bombs certainly fall in this category, whether one thinks that the circumstances required them or not.

Japanese cities destroyed by strategic bombing in World War II. More information about this map here.

Japanese cities destroyed by strategic bombing in World War II. More information about this map here.

The second place I depart is a technical one. There are several important differences between the effects of firebombing and atomic bombing. They are not, even in the case of the bombing of Japan, strictly equivalent from the point of view of their effects or their outcomes.

The Tokyo firebombing raid was a relatively slow (compared to an atomic bomb), massively-distributed attack. The Tokyo raid involved hundreds of B-29 bombers arriving and attacking over the course of several hours. Such massive groups of B-29s could be heard and tracked from a considerable distance. They spread their bombs over a large area of the city, with the goal of creating a mass conflagration that would be impossible to control. They could be fought against with interceptors and anti-aircraft guns; air-raid alarms could be sounded; civilians could flee to shelter, or outside of the city itself.  This is not to imply that any of these strategies were necessarily effective, and it does not necessarily make firebombing raids any more “humane.” But it does change the outcome quite a bit, when compared to an atomic bomb attack.

The atomic bombing raids of Hiroshima and Nagasaki were fast, near-instantaneous attacks. They involved a single B-29 weather plane in advance, and then two or three B-29s approaching the city, one with the bomb itself. This means that effective air-raid warning was minimal, because it was not possible to distinguish an atomic bomb attack from a reconnaissance or weather flight, all of which were common by that late stage in the war. (And obviously any hope of detecting an atomic bomb attack was impossible prior to Hiroshima.)

Drawing by Goro Kiyoyoshi of his memories of the Hiroshima attack. "I got on a streetcar of the Kabe line about 8:10 AM. The door was open and I was standing there. As I heard the starting bell ring, I saw a silver flash and heard an explosion over the platform on which l had just walked. Next moment everything went dark. Instinctively I jumped down to the track and braced myself against it. Putting a handkerchief to my mouth, I covered my eyes and ears with my hands."

Drawing by Goro Kiyoyoshi of his memories of the Hiroshima attack. “I got on a streetcar of the Kabe line about 8:10 AM. The door was open and I was standing there. As I heard the starting bell ring, I saw a silver flash and heard an explosion over the platform on which l had just walked. Next moment everything went dark. Instinctively I jumped down to the track and braced myself against it. Putting a handkerchief to my mouth, I covered my eyes and ears with my hands.” From Unforgettable Fire: Drawings by Atomic Bomb Survivors (1977).

The primary acute effects of the atomic bombs were blast and thermal radiation. The former travels at the speed of sound, the latter significantly faster. (The rays are transmitted at more or less the speed of light, but the intensity and duration of the thermal pulse is a more complex phenomena and unfolds over the course of several seconds.) The blast knocks down buildings. The thermal radiation heats and burns. Both contribute to the starting of fires — the thermal radiation directly (for certain materials), the blast wave indirectly by knocking over flammable materials, stoves, candles, etc. After Hiroshima there was a significant firestorm, as with incendiary bombing, but there was not after Nagasaki. There was no effective preparation for such an attack — perhaps if they had the foresight of some later Civil Defense techniques, some lives could have been saved (different shelter types did affect the fatality rates significantly, even close in to the zero point), but obviously this was not quite in the cards during the war itself, when the atomic bomb was such a novelty. There was no time for shelters, no time to flee the city, no time even for real comprehension of what was happening — a bright light followed by a crushing blast, followed by fire. For those who survived the blast and fire, there were radiation effects, if they were with a few kilometers of the epicenter. This could range from acute radiation sickness and death with several weeks, to an increased cancer risk over the course of their lives.

Are the atomic bomb effects significantly different from firebombing to warrant putting them into different ethical or moral categories? One could argue the point either way. I tend to think that they are both pretty terrible forms of suffering, but they are not identical. In many ways the atomic bombing effects were significantly worse for the people living in the target cities — all of the suffering of firebombing accelerated, with a few new terrors added into the mix, and with less warning.

Table from a 1963 Office of Civil Defense report, "Survey of the Thermal Threat of Nuclear Weapons," by Jack C. Rogers and T. Miller. These numbers are not necessarily authoritative, but they give some indication of the relative mortality rates differences I am talking about.

Table from a 1963 Office of Civil Defense report, “Survey of the Thermal Threat of Nuclear Weapons,” by Jack C. Rogers and T. Miller. These numbers are not necessarily authoritative, but lay out the situation well: atomic bombs have much higher mortality and casualty rates per square mile than firebombing, but destroy proportionally smaller amounts of area.

But the equivalence argument also misses some important differences in how deadly the atomic bombs were. The firebombing of Tokyo did, indeed, kill the most people of any air raid in history — from 80,000 to over 100,000 dead in a single raid. But the city of Tokyo had some 5 million people living in it. In the areas targeted, there were 1.5 million people living. So that means that it killed no more than 2% of the total population of the city, and no more than 7% of the people who lived in the targeted areas. The bombing of Hiroshima killed between 90,000 and 160,000 people in a city of 345,000 or so. So that is a fatality rate of 26-46%, depending on whose fatality estimates you go with. The bombing of Nagasaki killed between 39,000 to 80,000 people in a city of 260,000 people or so. So that is a fatality rate of 15-30%.

So to put it another way, the Hiroshima bombing was around 5 times more deadly than the Tokyo raid per capita, and the Nagasaki bombing was maybe 4 times more deadly. The total number dead is similar in all three cases, but the total number of people possible to kill in Tokyo was much higher than the number of people in Hiroshima and Nagasaki.

This isn’t the whole story, though. There is a subtle technical difference mixed in here. Firebombing on par with the Tokyo raid spread a moderate chance of death over a large area. The atomic bombs dropped in World War II spread a very high chance of death over a relatively small area. So depending on the target in question, the difference in fatalities might or might not matter. The Hiroshima bomb was perfectly capable of killing something like half of the city — but it was a pretty small city, compared to Tokyo. Tokyo has areas of incredibly high density, but also large areas of relatively moderate to low density.

So why does this matter? From an ethical standpoint, I’m not sure it does. The targeting of civilians for mass destruction seems to be the core ethical issue, whether you do this by means of fire, neutrons, or toxic gas. But I do think we end up underestimating the effects of the atomic bombs if we see them as exactly equivalent to firebombs. There is an error in seeing the atomic bombs as just an expeditious form of firebombing — it both overstates the deadliness of firebombing while understating the deadliness of atomic bombs.

This map gives a rough indication of the methodology used to construct the casualty estimates for a Little Boy bomb targeted on World War II Tokyo. Percentages are expected average fatality rates. The actual method used (see below) used many more gradations of difference. One can see, though, the way in which the most intense of the effects of the atomic bomb are highly localized relative to the total size of Tokyo.

This map gives a rough indication of the methodology used to construct the casualty estimates for a Little Boy bomb targeted on World War II Tokyo. Percentages are expected average fatality rates. The actual method used (see below) used many more gradations of difference. One can see, though, the way in which the most intense of the effects of the atomic bomb are highly localized relative to the total size of Tokyo. The underlying population density map of Tokyo comes from the very useful Japanairraids.org.

All of this is what led me to the question I opened with: What if, in some hypothetical alternative universe, instead of launching a firebombing raid in early March 1945, the US was able to drop the Little Boy atomic bomb onto Tokyo? What would the casualties have been for that raid?

Obviously an exact answer is not possible. But we do have population density maps of Tokyo, and we do have records on the relationship between distance from “ground zero” and percentage of population killed. There are lots of uncertainties, here, regarding the types of buildings, the differences in geography, and other things that are hard to estimate. But let’s do a rough estimation.

If we transpose the effects of Hiroshima — a 15 kiloton bomb detonated around 1,968 feet above the ground — to the population densities of Tokyo, what is the result? I don’t want to clog up the blog post with a detailed explanation of the methodology I’ve used, so I’m putting it at the end with the footnotes. The basic gist of it was this: I took a population density map of Tokyo from 1940, divided the different density areas into different layers in Photoshop, then selected radii based on bomb effects and did pixel counting. I used all of this to come up with rough minimum-maximum estimates of how many people lived in areas at different regions from the bomb blast, and then multiplied those population counts against known average fatality/casualty rate data taken from Hiroshima.

I looked at two ground zeros, to further emphasize the intense locality of a Hiroshima-sized atomic bomb attack (compared to a firebombing raid). If targeted on the moderately-dense Honjo area (which is more or less the center of the firebombing attack), one could roughly expect there to be between 213,000 and 344,000 fatalities, and between 442,000 and 686,000 injuries. This is the ground zero shown in the above image. If you move it north-west by only 1 km, though, to the more densely populated Asakusa area, the numbers change to 267,000 to 381,000 dead and 459,000 to 753,000 injured.

So if the Hiroshima bomb had been dropped on Tokyo, it probably would have destroyed less area than the March 1945 Tokyo firebombings — something like 5 square miles, compared to the 15 square miles destroyed by firebombing. However it would have killed between two and four times as many people who died in the firebombings, and injured possibly fewer or the same amount of people.

These numbers seem roughly plausible to me, even given all of the uncertainties involved, and they align with the rough guess one would make from the relative area destruction and casualty rates cited earlier. It is of note that the shifting of an atomic bomb’s aiming point can increase total casualties by several tens of thousands of people in a city the density of Tokyo; firebombing is probably not quite as dependent on any given aiming point, given how much lower the accuracy was.

Finally, it is worth noting that the Tokyo firebombing was much more fatal than most of the other firebombing raids. As the first low-altitude, massed night B-29 incendiary raid, against Japan’s highest-density city, it was especially fatal. Later raids killed, on average, orders of magnitudes less, both for the reasons given at the beginning (e.g. fleeing when you hear hundreds of B-29s in the distance), and because of much lower population densities. Had Hiroshima been firebombed, the fatalities would have certainly been much lower than the atomic bombings, because the Tokyo case is in fact an anomalously high one.

Atomic bombings may be ethically no better or worse than firebombing raids like Tokyo, but to regard them as simply an expedient form of firebombing misses a key point about their relative deadliness: If you have to pick, and you get to pick, one should choose to be firebombed, not atomic bombed — unless you know exactly where the bombs are going to go off.

Click for the full casualty calculation methodology.

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Posted in Meditations | This post has footnotes | 10 Comments »

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