Redactions

What did Bohr do at Los Alamos?

by Alex Wellerstein, published May 11th, 2015

In the fall of 1943, the eminent quantum physicist Niels Bohr managed a dramatic escape from occupied Denmark, arriving first in Sweden, then going to the United Kingdom. He was quickly assimilated into the British part of the Manhattan Project, then well underway. Bohr’s institute in Copenhagen had long been considered the world center of theoretical physics, and in the 1920s, young students from around the world flocked to work with him there. Now, in December 1943, Bohr and his son Aage made their pilgrimage to what was quickly becoming the new, stealth center of nuclear expertise: Los Alamos. At age 59, he would be the oldest scientist on “the Hill,” a place where the average age was 29.

Bohr skiing at Los Alamos, January 1945, seemingly without a care in the world. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

Bohr skiing at Los Alamos, January 1945, seemingly without a care in the world. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

This much is a standard part of Manhattan Project lore. Bohr’s contributions are usually spoken of primarily in psychological and moral terms. Bohr inspired the physicists to think about the consequences of their work, and laid the seeds of what would become the effort for postwar international control. He also spoke with both Churchill and Roosevelt, ineffectively, about the need to avoid an arms race. Bohr was a notoriously poor oral communicator, typically being barely audible. His deeply alienated and disturbed Churchill, who thought he might be proposing to tell the Soviets about the weapon. He probably just bored Roosevelt.

Some of the stories of his conduct at Los Alamos are adorably absent-minded. One of my favorite memos in the Manhattan Project archives is a February 1944 letter from Lt. Col. John Lansdale, head of MED security, to Richard Tolman, a physicist who was a good friend of the Bohrs. “Subject: Nicholas Baker,” it starts out, using Bohr’s wartime codename, and explains that in the process of following Bohr around, to make sure he was safe, some, well, deficiencies in his judgment were encountered:

“Both the father and son appear to be extremely absent-minded individuals, engrossed in themselves, and go about paying little attention to any external influences. As they did a great deal of walking, this Agent had occasion to spend considerable time behind them and observe that it was rare when either of them paid much attention to stop lights or signs, but proceeded on their way much the same as if they were walking in the wood. On one occasion, subjects proceeded across a busy intersection against the red light in a diagonal fashion, taking the longest route possible and one of greatest danger. The resourceful work of Agent Maiers in blocking out one half of the stream of automobile traffic with his car prevented their possible incurring serious injury in this instance.”

… I understand that the Bakers will be in Washington in the near future, at which time you will unquestionably see them. If the opportunity should present itself, I would appreciate a tactful suggestion from you to them that they should be more careful in traffic.

Nobel-Prize winning physicist nearly run over by a car, because he treats American streets like paths in a forest, saved from disaster only by a trailing secret agent blocking the road with his car? You can’t make this stuff up. These kinds of stories reinforce the playful, harmless, “Uncle Nick” character that Bohr has come to represent in this period.

Bohr and General Groves' personal technical advisor, Richard Tolman, attending the opening of the Bicentennial Conference on "The Future of Nuclear Science," circa 1947. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

Bohr and General Groves’ personal technical advisor, Richard Tolman, attending the opening of the Bicentennial Conference on “The Future of Nuclear Science,” circa 1947. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

But the truth is a little more complicated. For his part, Bohr would later downplay his role in the actual creation of nuclear weapons. He told another physicist in 1950, for example, that he had spent most of his time while in the United States trying to forestall a nuclear arms race. “That is why I went to America… They didn’t need my help in making the atom bomb,” he later said.

Did they need Bohr? Probably not — they probably would have managed well enough without him. But this is an odd standard for talking about one’s role in making a weapon of mass destruction. They didn’t need almost any individual who worked on the bomb, in the sense that they could have salvaged on without them.

And not being “needed” does not really get one off the hook, does it? Which gets at what I think is a key point here: in the postwar, Bohr never relied on his contributions to the bomb as a means of claiming moral superiority, responsibility, or political leverage. He was active in attempts to promote international control and avoid an arms race, but he didn’t do so in a way that ever owned up to his own role in making the bomb. As a result, a lot of people seem to believe that Bohr didn’t really do that much at Los Alamos other than provide the aforementioned moral support and provocative questions.

In fact, Bohr did work on the bomb. And not just on esoteric aspects of the physics, either; one of his role was concerned with the very heart of the “Gadget.”

Niels Bohr (r) conversing animatedly with his son Aage in front of a board full of equations. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

Niels Bohr (r) conversing animatedly with his son Aage in front of a board full of equations. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

One of the key parts of the implosion design for the atomic bomb (the same sort of bomb detonated at Trinity and over Nagasaki) is the neutron initiator that sits at the absolute center of the device. It is a deceptively tricky little contraption. At the instance of maximum compression, it needs to send out a small burst of neutrons, to get the whole chain reaction started. It’s not even that many neutrons, objectively speaking — on the order of a hundred or so in the first bombs. But conjuring up a hundred neutrons, at the center of an imploding nuclear assembly, at just the right moment, was a tricky technical problem, apparently.

The details are still classified-enough that figuring out exactly what the nature of the problem is proves a little tough in retrospect. In an interview many years later, the physicist Robert Bacher, head of G (Gadget) Division during the war, recalled that for whatever reason, Enrico Fermi had become particularly focused on the initiator as the lynchpin of the bomb, and maybe his own conscience:

I think Fermi began to be very worried about the fact that this terrific thing that he’d sort of been the father of was going to turn into a great big weapon. I think he was terribly worried about it. … I think he [Fermi] was worried about the whole project, not just the initiator. But focusing on the initiator was the one thing that he thought he could look at. The thing really might not work.

And I think he also felt an obligation to take something that was as hare-brained as this was and try to find a way in which it really wouldn’t work. So he did look into every sort of thing, and I think every second day or so for a period, I’d see him and he’d come up or he’d see Hans [Bethe] and come up with a new reason why the initiator wouldn’t work. …

Bacher got sick of Fermi’s interference, and eventually went to Oppenheimer to complain. Bacher recalled:

I said, “What I’d like to do is, Uncle Nick is here now, and I’d like to go and explain to him about the initiator and say I’d like his advice and counsel on whether he thinks it will work or not. We’ll answer any question that he puts to us, that we know the answer to.” So we did and he agreed with us and I told him quite frankly, “One of the reasons that we want to do this is that Fermi has so many misgivings about initiators.”

So I talked to him for a long while and then he spent about two days with his son Aage going over every single thing that had been done on this business. I saw him after this and he said, “My that’s very impressive. I think that will work.” I said, “Well now comes the test. Will you talk to Fermi about this? The two of you talk together and give me some counsel of what’s up on this?” So he did. And it made a lot of difference to have Uncle Nick talk to Fermi, because he felt that this wasn’t somebody you had working on some particular model and so on. It was sort of somebody from the outside, and I think it made Fermi feel a lot happier. And it certainly made it a lot easier for us.

The initiator that “Uncle Nick” convinced Fermi of, the one that they ended up using in the Trinity and Nagasaki bombs, was the “Urchin.”

A schematic of the “Urchin,” as imagined by me, based on a postwar British account.

It was a hollow sphere of beryllium, a mere two centimeters in diameter. The inner side of the sphere was machined with grooves, facing inwards. At the center of these grooves was another sphere of beryllium, centered by pins embedded in the outer shell. On both the inner grooves of the outer shell, and the outer surface of the inner sphere were coated with nickel and gold. Onto the nickel of the inner sphere was a thin film of virulently radioactive polonium. Polonium emits alpha particles; in the non-detonated state of the “Urchin,” these would be absorbed harmlessly by the gold and nickel. But when the bomb came imploding in around it, the beryllium and polonium would be violently mixed, producing a well-known reaction (beryllium + an alpha particle = carbon + neutron) that produced the necessary neutrons.

Margrethe and Niels Bohr converse in Copenhagen, 1947, in this extremely rare color photo. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

Margrethe and Niels Bohr converse in Copenhagen, 1947, in this extremely rare color photo. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

“Urchin” wasn’t the only initiator design on the table. Fermi apparently favored a design with the codename “Grape Nuts.” What was “Grape Nuts”? I have no idea — it’s still classified. Presumably these names meant something, since “Urchin” seems to reference the internal spikes. A topic listing for a May 1945 laboratory colloquium at Los Alamos discussed three initiator designs and their creators: “Urchin,” attributed to James Tuck and Hans Bethe; “Melon-Seed,” attributed to James Serduke; and, lastly, “Nichodemus,” attributed to… Nicholas Baker, the codename for Niels Bohr.

In the recently-declassified Manhattan District History, there are several paragraphs on Bohr. Most of them describe theoretical work he did on the physics of nuclear fission after arriving at the lab, which “cleared up many questions that were left unanswered before.” His work affected their understanding the nuclear properties of tamper materials, and he apparently gave them ideas for “new and better methods… of alternative means of bomb assembly.” (All of which apparently just pointed to the superiority of implosion, in the end, but still.)

MHD Bohr contributions to bomb

At least one sentence in the Manhattan District History is still completely blacked out. Maybe it refers to the initiator design (which the previous sentence refers to), maybe it refers to something else. It’s interesting that seven decades later, something of what Bohr worked on was still considered too classified to reproduce — evidence that Bohr’s influence on the bomb was less trivial than he would later make it out to be.

Why does it matter? In Michael Frayn’s Copenhagen, there is, towards the end of the play, an implied asymmetry between Bohr and Heisenberg. Heisenberg is criticized throughout the play for potentially making an atomic bomb for Hitler. The play ultimately says Heisenberg didn’t make an atomic bomb in part because he wasn’t trying to make a bomb. (It does so with perhaps a little bit too much credence to the “he didn’t do it because he was sabotaging it thesis,” which I think there is no evidence for and no reason to believe, but anyway.) Driven by his fears, Bohr goes to the United States and actually does work on the bomb, does contribute to the killing of over a hundred thousand people, and so on. And so there is some irony there, where Heisenberg, supposedly the one in a state of moral jeopardy, is the one who actually contributes to the death of no one, where Bohr, supposedly the moral authority, is the one who helps build the bomb.

Bohr with Elisabeth and Werner Heisenberg in Athens, Greece, 1956. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

Bohr with Elisabeth and Werner Heisenberg in Athens, Greece, 1956. Source: Emilio Segrè Visual Archives, Niels Bohr Library, American Institute of Physics.

Do Bohr’s contributions to the atomic bomb, however major or minor, weaken his moral authority? I don’t really think so. Bohr’s strongest and most lasting contribution was putting the bug of international control into the heads of people like Oppenheimer. That bug might have come up on its own (when they learned about Bohr’s scheme, Vannevar Bush and James Conant were surprised to find that they had been thinking along almost exactly the same lines, completely independently), but Bohr’s influence on openness, candor, the moral obligation of scientists, and so on had a profound effect on postwar political discourse, even if his dreaded arms race was not avoided. In this light, I think Bohr still comes off pretty well, even if the bomb still does contain traces of his fingerprints.

Visions

Critical mass

by Alex Wellerstein, published April 10th, 2015

When we talk about how nuclear weapons work, we inevitably mention the “critical mass.” This is the amount of fissile material you need to create a self-sustaining nuclear reaction. But it’s a very tricky concept, one often poorly deployed and explained, and the result, I have found while teaching and while talking to people online, is an almost universal confusion about what it means on a physical level.

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

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

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

Why use “critical mass” instead of other terms? For one thing, talking about the mass can help you get a sense of the size of the problem when fissile material is scarce and hard to produce (producing fissile material consumed 80% of the Manhattan Project’s budget). And it can also help you when talking about safety questions — about avoiding a nuclear reaction until you absolutely want on. So you don’t want to inadvertently create a critical mass. And knowing that the critical mass is so many kilograms of fissile material, as opposed to so many tons, was an early and important step in deciding that an atomic bomb was feasible in the first place.

A 5.3 kg ring of 99.96% pure plutonium-239. Under some conditions, this is enough to produce a significant explosive output. In its current form — unreflected, at normal density, in a ring-shape that prevents any neutrons from finding too many atoms to fission with — it is relatively innocuous.

A 5.3 kg ring of 99.96% pure plutonium. Under some conditions, this is enough to produce a significant explosive output. In its current form — unreflected, at normal density, in a ring-shape that prevents any neutrons from finding too many atoms to fission with — it is relatively innocuous.

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

Put simply, the amount of fissile material you need to start a nuclear reaction varies by the conditions under which it is being considered. The mass of material matters, but only if you specify the conditions under which it is being kept. Because under different conditions, any given form of fissile material will have different critical masses.

I’ve seen people (mostly online) want to talk about how nuclear weapons work, and they look up what “the” critical mass of uranium-235 is, and they find a number like 50 kg. They then say, OK, you must need 50 kg to start a nuclear reaction. But this is wrong. 50 kg of uranium-235 is the bare sphere critical mass of uranium-235. In other words, if you assembled 50 kg of uranium-235 into a solid sphere, with nothing around it, at normal atmospheric conditions, it will start a self-sustaining chain reaction. It probably would not produce an explosion of great violence — the uranium sphere would probably just blow itself a few feet apart (and irradiate anyone nearby). But once blown apart, the reaction would stop. Not a bomb.

The Godiva Device, a "naked" (get it?) critical assembly used as a pulsed nuclear reactor at Los Alamos. A 54 kg near-bare sphere of 93.7% enriched uranium separated into three pieces. At left, it is separated safely — no reaction. At right, you see what happened when the pieces got close enough to start a critical reaction — not a massive explosion (thank goodness), but enough energy output to damage the machine, and to push those pieces of uranium far enough from each other that they could no longer react.

The Godiva Device, a “naked” (get it?) critical assembly used as a pulsed nuclear reactor at Los Alamos. A 54 kg near-bare sphere of 93.7% enriched uranium separated into three pieces. At left, it is separated safely — no reaction. At right, you see what happened when the pieces got close enough to start a critical reaction — not a massive explosion (thank goodness), but enough energy output to damage the machine, and to push those pieces of uranium far enough from each other that they could no longer react. The workers were fortunately a safe distance away.

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

Is 50 kg the amount you need for a bomb? No. You can get away with much smaller numbers if you change the conditions. So if you put a heavy, neutron-reflecting tamper around the uranium, you can get away with around 10 to 15 kg of uranium-235 for a bomb — a factor of 3-5X less mass than you thought you needed. If your uranium-235 is dissolved in water, it takes very low masses to start a self-sustaining reaction — a dangerous condition if you didn’t mean to start one! And it may be possible, under very carefully-developed conditions, to make a bomb with even smaller masses. (The bare-sphere critical mass of plutonium is around 10 kg, but apparently one can get a pretty good bang out of 3-4 kg of it, if not less, if you know what you are doing.)

Conversely, does this mean that you can’t possibly have 50 kg of uranium (or more) in one place without it detonating? No. If your uranium is fashioned not into a solid sphere, but a cylinder, or is a hollow sphere, or has neutron-absorbing elements (i.e. boron) embedded in it, then you can (if you know what you are doing) exceed that 50 kg number without it reacting. And, of course, there are also impurities — the amount of uranium-238 in your uranium-235 will increase the size of any critical mass calculation.

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

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

Re-creation of Louis Slotin’s fatal experiment with the third plutonium core. The problem wasn’t the mass of the core, it was that Slotin inadvertently changed the state of the system (by accidentally letting the reflector drop onto it completely when his screwdriver slipped), which took a safe, non-critical assemble of plutonium and moved it into a briefly-critical state. This produced no explosion, but enough radiation to be fatal to Slotin and damaging to others in the room.

The classic example of this, of course, is the implosion bomb design. The bare sphere critical mass of plutonium-239 is 10 kg. The Nagasaki bomb contained 6.2 kg of plutonium as its fuel. At normal, room-temperature densities, a solid sphere of 6.2 kg of plutonium is not critical. Increase its density by 2.5X through the careful application of high explosives, however, and suddenly that is at least one critical mass of plutonium. Even this is something of an oversimplification, because it’s not just the density that matters: the allotropic (chemical) phase of plutonium, for example, affects its critical mass conditions (and plutonium is notorious for having an unusual number of these phases), and the Nagasaki bomb also included many other useful features meant to help the reaction along like a neutron initiator (which gave it a little shot of about 100 neutrons to start things off), and a heavy, natural-uranium tamper.

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

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

Supercriticality, which is what is more important for bomb design (and the initial stages of running a reactor) is when your system produces more than one extra neutron in each generation of fissioning. So if our uranium atom splits, produces 2 neutrons, and each of those go on to split more atoms, we’re talking about getting two neutrons for every one we put into the system. This is an exponentially-growing number of neutrons. Since neutrons move very quickly, and each reaction takes place very quickly (on the order of a nanosecond), this becomes a very large number of neutrons very quickly. Such is a bomb: an exponential chain reaction that goes through enough reactions very quickly to release a lot of energy.

The Trinity Gadget - Sectional View

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

So what are the conditions that produce these results? Well, it’s true that if you pure enough fissile material in one place, in the right shape, under the right conditions, it’ll become critical. Which is to say, each neutron that goes into the material will get replaced by at least another neutron. It will be a self-sustaining reaction, which is all that “criticality” means. Each fission reaction produces on average 2.5 more neutrons, but depending on the setup of the system, most or all of those may not find another fissile nuclei to interact with. If, however, the system is set up in a way that means that the replacement rate is more than one neutron — if every neutron that enters or is created ends up creating in turn at least two neutrons — then you have a supercritical system, with an exponentially-increasing number of neutrons. This is what can lead to explosions, as opposed to just generating heat.

In a bomb, you need more than just a critical reaction. You need it to be supercritical, and to stay supercritical long-enough that a lot of energy is released. This is where the concept of efficiency comes into play. In theory, the Fat Man’s 6.2 kg of plutonium could have released over 100 kilotons worth of energy. In practice, only about a kilogram of it reacted before the explosive power of the reaction separated the plutonium by enough that no more reactions could take place, and “only” released 20 kilotons worth of energy. So it was about 18% efficient. The relative crudity of the Little Boy bomb meant that only about 1% of its fissile material reacted — it was many times less efficient, even though it had roughly 10X more fissile material in it than the Fat Man bomb. The concept of the critical mass, here, really doesn’t illuminate these differences, but an understanding of how the critical reactions work, and how the overall system is set up, does.

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

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

Critical Assembly Simulator

The gist of this application is that the red atoms are uranium-235 (or plutonium), and the blue atoms are uranium-238 (or some other neutron-absorbing substance). Clicking on an atom will cause it to fission, and clicking on the “fire neutron initiator” button will inject a number of neutrons into the center of the arrangement. If a neutron hits a red atom, it has a chance to cause it to fission (and a chance to just bounce off), which releases more atoms (and also pushes nearby atoms away). If it hits a blue atom, it has a chance to be absorbed (turning it purple).

The goal, if one can put it that way, is to cause a chain reaction that will fission all of the atoms. As you will see from clicking on it, in its initial condition it is hard to do that. But you can manipulate a whole host of variables using the menu at the right, including adding a neutron reflector, changing the number of atoms and their initial packing density, the maximum number of neutrons released by the fission reaction, and even, if you care to, changing things like the lifetimes of the neutrons, the likelihood of the neutrons just scattering off of atoms, and whether the atoms will spontaneously fission or not. If you have a reflector added, you can also click the “Implode” button to make it compress the atoms into a higher density.

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

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

This is not a real physical simulation of a bomb, obviously. None of the numbers used have any physically-realistic quality to them, and real atomic bombs rely on the fissioning of trillions of atoms in a 3D space (whereas if you try to increase the number of atoms visible to 1,000, much less 10,000, your browser will probably slow to a crawl, and this is just in 2D space!). And this simulator does not take into account the effects of fission products, among other things. But I like that it emphasizes that it’s not just the number of atoms that determines whether the system is critical — it’s not just the mass. It’s all of the other things in the system as well. Some of them are physical constants, things pertaining to the nature of the atoms themselves. (Many of these were constants not fully known or understood until well after 1939, which is why many scientists were skeptical that nuclear weapons were possible to build, even in theory.) Some of them are engineering tricks, like the reflector and implosion.

My hope is that this kind of visualization will help my students (and others) think through the actual reaction itself a bit more, to help build an intuitive understanding of what is going on, as a remedy to the aspects of a prior language that was created by scientists, diffused publicly, and then got somewhat confused. “Critical mass” isn’t a terrible term. It has its applications. But when it can lead to easy misunderstandings, the language we choose to use matters.

News and Notes | Redactions

H-bomb headaches

by Alex Wellerstein, published March 27th, 2015

Once again, the US government has gotten itself into a bad situation over the supposed secret of the hydrogen bomb. As The New York Times reported earlier this week, the Department of Energy (DOE) censors demanded that the physicist Ken Ford heavily redact a manuscript he had written on the history of the hydrogen bomb. Ford, however, declined to do so, and you can buy the unexpurgated text right now on Amazon in Kindle format, and in hardback and paperback fairly soon.

Ken Ford by Mark Makela for the New York Times.

Ken Ford by Mark Makela for the New York Times.

Ford was a young physicist working with John A. Wheeler during the 1950s, and so a lot of his book is a personal memoir. He is also (in full disclosure) the former head of the American Institute of Physics (my employer from 2011-2014), and I was happy to give him some assistance in the preparation of the manuscript, mainly in the form of tracking down declassified/unclassified sources relating to his story, and helped him get solid citations to them. Ken actually just recently came to Hoboken so we could iron out a few of the final citations in a Starbucks near my apartment. I knew he was having some issues with classification review, but I didn’t know he was going to play it like this — I am impressed by his boldness at just saying “no” to DOE.

Nothing I saw in his work struck me as anything actually still secret. Which is not to say that it might or might not be officially classified — just that the technical information is much the same kind of technical information you can find in other, unclassified sources, like the books of Richard Rhodes and Chuck Hansen, and people on the web like Carey Sublette, among others. And therein lies the rub: is information still a secret if it is officially classified, even if it is widely available?

This has been a tricky thing for the government to adjudicate over the years. The Atomic Energy Act of 1946 (and its revisions) charges the Atomic Energy Commission (AEC), and later the Department of Energy, with regulating “restricted data” wherever it appears, wherever it comes from. According to the law, they don’t have any choice in the matter. But over the years they changed their stance as to the best way to achieve this regulation.

One of the earliest decisions of the Lilienthal AEC was to adopt a “no comment” policy with regards to potentially sensitive information published by people unassociated with the nuclear weapons complex. Basically, if someone wanted to speculate on potentially classified topics — like the size of the US nuclear stockpile, or how nuclear weapons worked — the AEC in general would not try to get in their way. They might, behind the scenes, contact editors and publishers and make an appeal to decency and patriotism. (Sometimes this got expressed in a comical fashion: they would have “no comment” about one paragraph but not another.) But they generally did not try to use threat of prosecution as the means of achieving this end, because they felt, correctly, that censorship was too blunt an object to wield very effectively, and that telling someone on the outside of the government that they had hit upon classified information was tantamount to revealing a secret in and of itself.

Howard Morland then-and-now. On the left, Morland and his H-bomb model, as photographed for the Washington Post in 1981 (at the time his book account of the Progressive case, The Secret that Exploded, was published). At right, Morland and me at a party in Washington, DC, just before I moved to New York. He is wearing his H-bomb secret shirt he had made in 1979 (which he discusses in his book). I felt very honored both to see the original shirt and to see the pose he imagined he might do with it before the press, to reveal the secret to the world.

Howard Morland then and now. On the left, Morland and his H-bomb model, as photographed for the Washington Post in 1981 (at the time his book account of the Progressive case, The Secret that Exploded, was published). At right, Morland and me at a party in Washington, DC, just before I moved to New York. He is wearing his H-bomb secret shirt he had made in 1979 (which he discusses in his book). I felt very honored both to see the original shirt and to see the pose he imagined he might do with it before the press, to reveal the secret to the world.

There were a few instances, however, where this “no comment” policy broke down. The best-known one is the case of United States v. Progressive, Inc. in 1979. This is the famous case in which the DOE attempted to obtain (and was briefly granted) prior restraint against the publication of a magazine that claimed to contain the “secret of the hydrogen bomb,” written by the journalist/activist Howard Morland. The DOE convinced a judge to grant a restriction on publication initially, but in the appeals process it became increasingly clear that the government’s case was on fairly shaky grounds. They declared the case moot when the researcher Chuck Hansen had a paper on hydrogen bomb design published in a student newspaper — in this case, it looked like an obvious attempt to back out before getting a bad ruling. Morland’s article appeared in print soon after and became the “standard” depiction of how the Teller-Ulam design works, apparently validated by the government’s interest in the case.

In this case, the issue was about the most egregious incursion of the Atomic Energy Act into the public sphere: the question of whether the government could regulate information that it did not itself play a part in creating. The “restricted data” clause of the Atomic Energy Act (after which this blog is named) specifies that all nuclear weapons-related information is to be considered classified unless explicitly declassified, and makes no distinction about whether said information was created in a laboratory by a government scientist or anywhere else in the world by private citizens. Thus nuclear weapons information is “born secret” according to the law (unlike any other forms of controlled national defense information), which in cases like that of The Progressive puts it in direct conflict with the First Amendment.

Ford’s book is something different, however. Ford was himself a government scientist and had a security clearance. This means he was privy to information that was most definitely classified as both “restricted data” and national defense information. He worked on Project Matterhorn B at Princeton, which was part of the hydrogen bomb effort in the early 1950s. He signed contracts that governed his behavior, both while working for the government and later. He agreed to let the government evaluate his work for classified information, and agreed he would not give away any classified information.

At left, the redacted Bethe article as published in Scientific American, April 1950. At right, the original draft, redacted by the Atomic Energy Commission (photograph taken by me at the National Archives, College Park).

At left, the redacted Bethe article as published in Scientific American, April 1950. At right, the original draft, redacted by the Atomic Energy Commission (photograph taken by me at the National Archives, College Park).

There is a historical parallel here, and a better one than the Progressive case. In 1950, the magazine Scientific American ran a series of articles about the hydrogen bomb. The first of these was by the gadfly physicist Louis Ridenour. Ridenour had no connection with nuclear weapons work and he could say whatever he wanted. But the second was by Hans Bethe, who was intimately involved with classified nuclear work. Bethe obviously didn’t try to publish anything he thought was secret. But the AEC got several passages deleted from the article anyway.

The passages removed were extremely banal. For example, Bethe said that it seemed like they would need to use the deuterium-tritium reaction to achieve fusion. This level of basic information was already in the Ridenour article that was published a month before. So why delete it from the Bethe article? Well, because Bethe was connected with the government. If Ridenour says, “tritium is necessary,” it doesn’t mean that much, because Ridenour doesn’t have access to secrets. If Bethe says it, it could be potentially understood by an adversary to mean that the deuterium-deuterium reaction isn’t good enough (and it isn’t), and thus that the Los Alamos scientists had found no easy short-cut to the H-bomb. So the same exact words coming out of different mouths had different meanings, because coming out of Bethe’s mouth they were a statement about secret government research, and out of Ridenour’s mouth they were not. The whole thing became a major publicity coup for Scientific American, of course, because there is no better publicity for a news organization than a heavy-handed censorship attempt.

I have looked over a lot of Ford’s book. It’s available on Amazon as a e-book, or as a PDF directly from the publisher. I haven’t had time to read the entire thing in detail yet, so this is nothing like a formal review. The sections that I imagine drew the ire of the DOE concern some of the early thinking about how the Teller-Ulam design came about. This is an area where there is still a lot of historical ambiguity, because tracing the origins of a complex technical idea is not straightforward even without classification mucking things up. (I am working on a paper of this myself, and have a somewhat different interpretation than Ken, but that is really neither here nor there.)

Ken Ford Building the H-bomb

There’s nothing that looks classified in Ken’s work on this to me. There are references to things that generally don’t show up in government publications, like “equilibrium conditions,” but the existence of these kinds of technical issues are common in the open literature on thermonuclear weapons, and a lot of them are present in the related field of inertial confinement fusion, which was largely declassified in the late 1990s.

So why is the DOE pent up over Ford? It is probably not an issue of the content so much as the fact that he is the one talking about it. It is one thing for an unaffiliated, uncleared person like me to say the words “equilibrium conditions” and talk about radiation implosion and tampers and cryogenic cooling of plutonium and things of that nature. It’s another for a former weapons physicist to say it.

It’s also related to the fact that because Ken was a former weapons physicist, they have to review his work. And they have to review it against their official guides that tell them what is technically secret and what is not. And what is allowed by the DOE to talk about is not the same thing about what people on the outside of the DOE do talk about. So, for example, this is pretty much most of what the DOE considers kosher about thermonuclear weapons:

  • The fact that in thermonuclear (TN) weapons, a fission “primary” is used to trigger a TN reaction in thermonuclear fuel referred to as a “secondary.” 
  • The fact that, in thermonuclear weapons, radiation from a fission explosive can be contained and used to transfer energy to compress and ignite a physically separate component containing thermonuclear fuel.  Note: Any elaboration of this statement will be classified.
  • Fact that fissile and/or fissionable materials are present in some secondaries, material unidentified, location unspecified, use unspecified, and weapons undesignated. 

Now you can find a lot more elaboration on these statements in the works of Chuck Hansen, Carey Sublette, and, hell, even Wikipedia these days. (Fun fact: Howard Morland, of The Progressive case, is an active Wikipedian and contributor to that page.) And in fact there is a lot that has been released by the government that does lend towards “elaboration” of these statements, because it is impossible to full compartmentalize all of this kind of information in such neat little boxes.

But the job of the DOE reviewer was to sit down with the guide, sit down with Ken’s book, and decide what the guide said they had to do regarding the book. And in this case, it was about 10% of the book that the guide said they had to get rid of. And in this case, they are bound by the guide. Now, at a certain point, one has to say, if the guide is saying that lots of stuff that is already in Richard Rhodes’ Dark Sun, published 20 years ago, still needs to be kept under lock and key, well, maybe the guide needs to be changed. But there is arguably something of a difference between Rhodes (an outsider) writing things, and Ford (an insider) writing the same things. But it’s hard to see how any of this is going to matter with regard to national security today or in the future — it doesn’t seem like these kinds of statements are going to be what enables or disables future proliferators from acquiring thermonuclear weapons.

"How institutions appear / how institutions are." From one of my favorite comics published on Subnormality, by Winston Rowntree.

“How institutions appear / how institutions are.” From one of my favorite comics published on Subnormality, by Winston Rowntree.

What’s amazing, again, is not that the DOE told Ken to delete things from his book. That is somewhat expected given how the classification system works. What’s amazing is that Ken told them to shove off and published it anyway. That doesn’t happen so often, that a once-insider won’t play ball. And it has no doubt put the DOE in a tough situation: they’ve set things up for a good story (like the one in the New York Times) about the silliness of government secrecy, and as a result have probably resulted in a lot of book sales that wouldn’t have otherwise happened. In this case, their attempt at preserving some form of secrecy has certainly resulted in them just calling more attention to the work in question.

What can they do to Ken? Well, technically, they probably could prosecute him under the Atomic Energy Act, or potentially the Espionage Act. But I’m pretty sure they won’t. It would be a public relations nightmare for them, would probably result in the release of even more information they deem sensitive, and Ken is no rogue agent. Which just goes to highlight one of the points I always make when I talk to people about secrecy: from the outside, it can look like government institutions are powerful and omnipotent with regards to classification. But they are usually weaker and more frail than they appear, because those who are bound by secrecy usually end up losing the public relations war, because they aren’t allowed to participate as fully as those who are on the outside.

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To demonstrate, or not to demonstrate?

by Alex Wellerstein, published March 6th, 2015

As the atomic bomb was becoming a technological reality, there were many scientists on the Manhattan Project who found themselves wondering about both the ethics and politics of a surprise, unwarned nuclear attack on a city. Many of them, even at very high levels, wondered about whether the very threat of the bomb, properly displayed, might be enough, without the loss of life that would come with a military attack.

1945-06-12 - Franck Report

The Franck Report, written in June 1945 by scientists working at the University of Chicago Metallurgical laboratory, put it perhaps most eloquently:

the way in which nuclear weapons, now secretly developed in this country, will first be revealed to the world appears of great, perhaps fateful importance. … It will be very difficult to persuade the world that a nation which was capable of secretly preparing and suddenly releasing a weapon, as indiscriminate as the rocket bomb and a thousand times more destructive, is to be trusted in its proclaimed desire of having such weapons abolished by international agreement…. 

From this point of view a demonstration of the new weapon may best be made before the eyes of representatives of all United Nations, on the desert or a barren island. The best possible atmosphere for the achievement of an international agreement could be achieved if America would be able to say to the world, “You see what weapon we had but did not use. We are ready to renounce its use in the future and to join other nations in working out adequate supervision of the use of this nuclear weapon.”

They even went so far as to suggest, in a line that was until recently totally etched out of the historical record by the Manhattan Project censors, that “We fear its early unannounced use might cause other nations to regard us as a nascent Germany.” 

The evolution of the "Trinity" test fireball, at constant scale, with the Empire State Building for additional scale reference.

The evolution of the “Trinity” test fireball, at constant scale, with the Empire State Building for additional scale reference.

The idea of a “demonstration” was for many scientists a compelling one, and news of the idea spread to the various project sites. The idea would be to let the Japanese know what awaited them if they did not surrender. This would be more than just a verbal or textual warning, which could be disregarded as propaganda — they would set the bomb off somewhere where casualties would be low or minimal, but its nature easy to verify. If the demonstration did not work, if the Japanese were not receptive, then the bomb could be used as before. In the eyes of these scientists, there would be no serious loss to do it this way, and perhaps much to gain.

Of course, not all scientists saw it this way. In his cover letter forwarding the Franck Report to the Secretary of War, the physicist Arthur Compton, head of the Chicago laboratory, noted his own doubts: 1. if it didn’t work, it would be prolonging the war, which would cost lives; and 2. “without a military demonstration it may be impossible to impress the world with the need for national sacrifices in order to gain lasting security.” This last line is the more interesting one in my eyes: Compton saw dropping the bomb on a city as a form of “demonstration,” a “military demonstration,” and thought that taking a lot of life now would be necessary to scare the world into banning these weapons in the future. This view, that the bombs were something more than just weapons, but visual arguments, comes across in other scientists’ discussions of targeting questions as well.

Truman was never asked or told about the demonstration option. It is clear that General Groves and the military never gave it much thought. But the Secretary of War did take it serious enough that he asked a small advisory committee of scientists to give him their thoughts on the matter. A Scientific Panel, composed of J. Robert Oppenheimer, Arthur Compton, Enrico Fermi, and Ernest Lawrence, weighed in on the matter formally, concluding that: “we can propose no technical demonstration likely to bring an end to the war; we see no acceptable alternative to direct military use.”

"Recommendations on the Immediate Use of Atomic Weapons," by the Scientific Panel of the Interim Committee, June 16, 1945. The full report (which also discusses the possibility of the H-bomb and many other things) is extremely interesting, as well — click here to read it in its entirety.

“Recommendations on the Immediate Use of Atomic Weapons,” by the Scientific Panel of the Interim Committee, June 16, 1945. The full report (which also discusses the possibility of the H-bomb and many other things) is extremely interesting, as well — click here to read it in its entirety.

I find this a curious conclusion for a few reasons. For one thing, are these four scientists really the best experts to evaluate this question? No offense, they were smart guys, but they are not experts in psychological warfare, Japanese political thought, much less privy to intercepted intelligence about what the Japanese high command was thinking at this time. That four physicists saw no “acceptable alternative” could just be a reflective of their own narrowness, and their opinion sought in part just to have it on the record that while some scientists on the project were uncomfortable with the idea of a no-warning first use, others at the top were accepting of it.

But that aside, here’s the other fun question to ponder: were they actually unanimous in their position? That is, did these four physicists actually agree on this question? There is evidence that they did not. The apparent dissenter was an unlikely one, the most conservative member of the group: Ernest Lawrence. After the bombing of Hiroshima, Lawrence apparently told his friend, the physicist Karl Darrow, that he had been in favor of demonstration. Darrow put this into writing on August 9, 1945, to preserve it for posterity should Lawrence come under criticism later. In Darrow’s recollection, Lawrence debated it with the other scientists for “about an hour” — a long-enough time to make it seem contentious. On August 17, after the bomb had “worked” to secure the peace, Lawrence wrote back to Darrow, somewhat denying this account, saying that it was maybe only ten minutes of discussion. Lawrence, in this later account, credits Oppenheimer as being the hardest pusher for the argument that unless the demonstration took out a city, it wouldn’t be compelling. I’m not sure I completely believe Lawrence’s later recant, both because Darrow seemed awfully convinced of his recollection and because so much changed on how the bomb was perceived after the Japanese surrendered, but it is all an interesting hint as some of the subtleties of this disagreement that get lost from the final documents alone. In any case, I don’t know which is more problematic: that they debated for an hour and after all that, concluded it was necessary, or that they spent no more than ten minutes on the question.

1945-08-10 - Groves memo on next bombs

As an aside, one question that sometimes gets brought up at this point in the conversation is, well, didn’t they only have two bombs to use? So wouldn’t a demonstration have meant that they would have only had another bomb left, perhaps not enough? This is only an issue if you consider the timescale to be as it was played out — e.g., using both bombs as soon as possible, in early August. A third plutonium bomb would have been ready by August 17th or 18th (they originally thought the 24th, but it got pushed up), so one could imagine a situation in which things were delayed by a week or so and there would have been no real difference even if one bomb was expended on a demonstration. If they had been willing to wait a few more weeks, they could have turned the Little Boy bomb’s fuel into several “composite” core implosion bombs, as Oppenheimer had suggested to Groves after Trinity. I only bring the above up because people sometimes get confused about their weapon availability and the timing issue. They made choices on this that constrained their options. They had reasons for doing it, but it was not as if the way things happened was set in stone. (The invasion of Japan was not scheduled until November 1st.)

So, obviously, they didn’t choose to demonstrate the bomb first. But what if they had? I find this an interesting counterfactual to ponder. Would dropping the bomb in Tokyo Bay have been militarily feasible? I suspect so. If they could drop the bombs on cities, they could probably drop them near cities. To put it another way: I have faith they could have figured out a way to do it operationally, because they were clever people.

But would it have caused the Japanese high command to surrender? Personally, I doubt it. Why? Because it’s not even clear that the actual atomic bombings were what caused the Japanese high command to surrender. There is a strong argument that it was the Soviet invasion of Manchuria that “shocked” them into their final capitulation. I don’t know if I completely buy that argument (this is the subject of a future blog post), but I am convinced that the Soviet invasion was very important and disturbing to the Japanese with regards to their long-term political visions for the country. If an atomic bomb dropped on an actual city was not, by itself, entirely enough, what good would seeing a bomb detonated without destruction do? One cannot know, but I suspect it would not have done the trick.

The maximum size of a 20 kiloton mushroom cloud in Tokyo Bay, as viewed from the roof of the Imperial Palace today, as visualized by NUKEMAP3D. Firebombed Tokyo of 1945 would have afforded a less skyscraper-cluttered view, obviously.

The maximum size of the mushroom cloud of a 20 kiloton nuclear detonation in Tokyo Bay, as viewed from the roof of the Imperial Palace today, as visualized by NUKEMAP3D. Firebombed Tokyo of 1945 would have afforded a less skyscraper-cluttered view, obviously.

Of course, the Chicago scientists suspected that as well, but said it was necessary from a moral point of view. Sure, the Japanese might not surrender, but then, at least, you can say you showed them what was coming first.  As it was, we gave no real warning whatsoever before dropping it on Hiroshima. But here’s the question I come to next: could you demonstrate it, and then drop it on a city? That is, could the United States really say: “we have made this apocalyptic weapon, unleashed the atom, and many other peril/hope clichés — and we have chosen not to use it to take life… yet. But if you don’t give in to our demands, we will unleash it on your people.” How could that not look like pure blackmail, pure terrorism? Could they then turn around and start killing people by the tens of thousands, having announced their capability to do so? Somehow I suspect the public relations angle would be almost impossible. By demonstrating it first, they would be implying that they knew that it was perhaps not just another weapon, not just another way to wage war. And that acknowledgment would mean that they would definitely be seen as crossing a line if they then went on to use it.

As it was, that line, between the bomb as “just another weapon” and something “special,” was negotiated over time. I think the demonstration option was, for this reason, never really going to be on the table: it would have forced the American policymakers to come to terms with whether the atomic bomb was a weapon suitable for warfare on an earlier schedule than they were prepared to. As it was, their imagery, language, and deliberations are full of ambiguity on this. Sometimes they thought it would have new implications for “man’s position in the universe” (and other “special bomb” notions), sometimes they thought it was just an expedient form of firebombing with extra propaganda value because it would be very bright and colorful. Secrecy enabled them to hedge their bets on this question, for better or worse.

Without imagery like this, would the world fear nuclear weapons more, or less?

Without imagery like this, would the world fear nuclear weapons more, or less? When, if ever, would the first use of nuclear weapons in warfare have been?

So who was right? I don’t know. We can’t replay history to see what happened, obviously. I think the idea of a demonstration is an interesting expression of a certain type of ethical ideal, though it went so far against the practical desires of the military and political figures that it is hard to imagine any way it would have been pursued. I am not sure it would even have been successful, or resolved the moral bind of the atomic bomb.

I do find myself somewhat agreeing with those scientists who said that perhaps it was better to draw blood with the smaller, cruder bombs, before the really big ones came around — and they knew those were coming. If we didn’t have Hiroshima and Nagasaki, what would we point to, to talk about why not to use nuclear weapons? Would people think the bombs were not that impressive, or even more impressive than they were? I don’t know, but there is something to the notion that knowing the gritty, gruesome reality (and its limitations) is better than not. It took the Holocaust for the world to (mostly) renounce genocide, maybe it took Hiroshima and Nagasaki for the nuclear taboo to be established (arguably). That, perhaps, is the most hopeful argument here, the one that sees Hiroshima and Nagasaki as not just the first cities to be atomic bombed, but the last, but I am sure this is little solace to the people who were in those cities at the time.

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How to die at Los Alamos

by Alex Wellerstein, published February 13th, 2015

The people who ran the Manhattan Project worried about a lot of different things. Usually when we talk about this, it’s a story about the Germans, or the Japanese, or the physics, or other very specific things of that nature. But they also worried about banal things, like occupational safety: reducing the number of people injured, or killed, as part of doing their job.

Around half of the 500,000 or so people employed by the Manhattan Project were employed in construction. As a result, most of the injuries and fatalities associated with making the bomb were of a banal, construction-related variety. Heavy machinery, ditches, collapsing buildings — these were the most dangerous parts of the project for those who made it. Occasionally there were more exotic threats. Criticality accidents took the lives of two scientists in the immediate postwar, as is well known. Concerns about criticality excursions at the plants used to enrich uranium were a non-trivial concern. And there were other, more unusal ways to die, as you would expect from any body of people that large, working over so great an area, especially when they are concentrated in places that were for much of this period constant construction sites, as were Los Alamos, Oak Ridge, and Hanford.

Exhibit 14 - Fatalities at Los Alamos

“Exhibit 14: FATAL ACCIDENTS: Since the inception of the Project in the Spring of 1943, until September 1946, twenty-four (24) fatal accidents have occurred. The following history of these incidents was taken from hospital records, reports of investigation boards, and the safety division files.”

Some time ago I happened upon a list of all of the fatal accidents that occurred at Los Alamos between its inception in 1943 through September 1946. There were exactly twenty-four, an even two-dozen ways to die while working at an isolated nuclear weapons laboratory. I reprint them here, not only because there is a morbid fascination with this sort of thing, but because I’ve found that this list gives a really remarkable summary of the people of Los Alamos, the hazards of Los Alamos, and the work that goes into making a bomb, which requires much more than star physicists to pull off successfully. Each death was followed by an inquiry.

My summaries are below; the original document (linked to at the end of this post) contains more details on some of them. The copy of the document I have is very hard to read, so I may have gotten a few of the names wrong.

1943
  1. Estevan Roches, bulldozer operator. Crushed by a rock in his tractor while trying to build an access road to Los Alamos, at night. Died February 11, 1943.
  2. George H. Holtary, diesel motor mechanic. Was working on the power plant at Los Alamos, got crushed between a crankshaft and the housing. Died March 1, 1943.
  3. George J. Edwards, a soldier. Fell into a drainage ditch at night after drinking, injuring his back and puncturing his kidneys. Died July 19, 1943.
  4. Jose Montoya, construction laborer. Was digging an acid sewer ditch between “C” and “D” buildings. The 8-foot ditch was not reinforced and it collapsed on him. Died November 2, 1943. Investigation board recommended reinforcing ditches in the future.
  5. Pfc. Frederick Galbraith, military police. Was accidentally shot by another serviceman while sleeping. Another private was cleaning the gun and did not realize there was a live round in the chamber. It caused a severe wound in Galbraith’s thigh. He died of severe shock, November 4, 1943.
  6. Efren Lovato, construction laborer. Lovato was in the back of a dump truck being used to transport laborers to lunch. The truck’s accelerator got stuck and it crashed into a car at the pass gate and overturned, killing Lovato and another laborer, on November 20, 1943. Investigation board recommended increasing the size of the motor pool so the vehicles could be inspected more regularly.
  7. Fridon Virgil, construction laborer. Killed in the same accident as previous.
1944
  1. Fred Wolcott, contractor engaged to clear woods near the site. Attached a bulldozer to a tree and tried to pull it out. The tree snapped and fell on him. Witnesses say he appeared to be “frozen” to the seat of his tractor. Died May 9, 1944.
  2. Elmer R. Bowen, Jr., age 10 and a half. With a friend, was using a canoe from the former Los Alamos Ranch School in the main pond. His canoe capsized; neither him nor his friend could swim, and he drowned on July 1, 1944. He was the son of a maintenance mechanic, one who remained at Los Alamos for several decades after the war, until his retirement. Canoeing prohibited after death.
  3. Ernesto Freques, truck driver. He was standing next to a pile of reinforcing steel, unaware that workers on top were trying to move pieces and having difficulty because the steel was bent. The pile of steel collapsed on him; he was pinned against the truck, his heart lacerated. Died on July 6, 1944.
  4. Horace Russell, Jr., a research chemist, age 26. Fell from a horse while riding it in a canyon near the project. Suffered a serious head injury. Died August 5, 1944. The first of only four scientists on this list.
  5. Pfc. Hugo B. Kivsto, a member of the Provisional Engineer Detachment. Was fatally injured while driving an Army vehicle on a poorly graded surface of dirt road near Santa Cruz, New Mexico. Lost control of the vehicle while rounding a hazardous curve. Tried to jump clear of the truck as it went over the embankment and was pinned under it. Died on December 3, 1944.
 1945
  1. Pvt. Grover C. Atwell, member of Special Engineer Detachment. Assigned to hospital ward duty, died of an overdose of barbiturates taken from the hospital pharmacy. He died on July 21, 1945, but his body was not found until August 22, 1945. The report does not elaborate on why there was such a delay in finding his body. The investigation concluded he was “depressed over his assignment,” no indication of financial or family difficulties. Declared mentally irresponsible for his death, and thus his “death was in the line of duty and not a result of his own misconduct.”
  2. James W. Popplewell, civilian carpenter. Was working inside a building on August 7, 1945, at the same time a caterpillar tractor was pushing dirt over the roof. The roof collapsed and both tractor and dirt crushed Popplewell. Investigation blamed the foreman for not seeing if the building could support the load of the dirt and the tractor; the foreman was recommended for termination. This is a rare case of any liability being found.
  3. Harry Daghlian, physicist, age 24. Criticality accident with the so-called “demon core.” Report notes he “was exposed to too great radiation” on August 21, died on September 15, 1945. The report carries no further information on him and says that Health Physics is still investigating the matter. Second of the four scientists.
  4. Asa Houghton, civilian carpenter. Was going down the hill from project towards Santa Fe in his truck, front wheels locked and caused vehicle to run off the left side of the road, turned 5 or 6 times. Died of internal injuries on September 27, 1945.
1946
  1. Manuel Salazar, janitor. With three friends (also janitors), got extremely drunk on muscatel wine mixed with ethylene glycol (antifreeze). Died from ethylene glycol poisoning on January 29, 1945. Because deaths were not result of duty, descendants received no benefits of compensation.
  2. Alberto Roybal, janitor. Same event as above, same death date.
  3. Pedro Baca, janitor. Same event as above, same death date.
  4. Levi W. Cain, civilian blacksmith. Struck by car driven by a military sergeant on site. The sergeant was absolved of blame; the visibility was low, but car was not being driven at an excessive speed. Cain died on February 6, 1946.
  5. Louis Slotin, physicist, age 35. Criticality accident with the same core that killed Daghlian. While making measurements, “was exposed to radiation from radioactive materials” to a fatal degree. Third of the four scientists. Died on May 21, 1946. After Slotin’s death, criticality experiments were effectively put on hold until new safety guidelines could be devised.
  6. Livie R. Aguilar, truck driver for Zia Company. For reasons that were unknown (there were no witnesses or obvious evidence), his truck left the road and turned over into a trench, pinning Aguilard beneath it. He died on July 1, 1946.
  7. Joshua I. Schwartz, a scientist, age 21. With two other scientists (Robert A. Huffhines and William E. Bibbs), he was engaged in an experiment to trace air currents in Omega Canyon. They were instructed to use balloons or other non-flammable equipment for this. Instead, they tried to use smudge pots (smoke bombs). One of the smudge pots exploded, fatally injuring Schwartz, and critically injuring his companions (permanent blindness). Schwartz died on 2 August 1946. The investigation faulted their bosses with inadequate supervision. This resulted in at least one lawsuit over compensation. The fourth of four scientists.
  8. Herbert Schwaner, construction laborer. He was driving a bulldozer up a ramp when one of the treads locked, causing it to topple. He was pinned underneath. He was found five minutes later, by his brother, dead. He died on August 7, 1946.

It’s quite a list. Here is a copy of the original report, if you want more details on any of the above.

Los Alamos population estimates, 1943-1946. For a more detailed breakdown of civilian duties, see this payroll census. The big dip in 1943 seems to be something about reshuffling how construction labor was accounted for when the University of California took over.

Los Alamos population estimates, 1943-1946. For a more detailed breakdown of civilian duties, see this payroll census. The big dip in 1943 seems to be something about reshuffling how construction labor was accounted for when the University of California took over.

Construction dominates, but automobiles, recreational mishaps, and scientific experiments make their appearance. As does suicide — one wonders what the report means by “depressed over his assignment” for the soldier at the hospital. The presence of a child reminds us that families lived at this secret laboratory — by the end of the war there were some 1,500 “dependents,” many of them children, living at the project site.

The Hispanic and/or Indian names point towards Los Alamos’ location. On the list of properties near the site that was seized by the Army (via condemnation), there are many Roybals, Montoyas, and Gomezes. In the list of Los Alamos badges, there are many Bacas, Virgils, Montoyas, and a Salazar.  These are the people who lived there first, often written out of the more popular narratives of scientific triumph.

Even on the question of scientists, I was surprised to find two names I had not seen before: Russell and Schwartz. Both were young. Russell’s death adds a grim pall to all of that footage of scientists riding around in the woods on horses. Schwartz’s death is also a reminder of how much responsibility was thrust onto the young scientists — though frankly, it is maybe surprising that more people did not die this way, given the haste at which they worked and the toxicity, flammability, and radioactivity of the substances they were using.

Excerpt from a guide produced by the Oak Ridge Safety program.

Excerpt from a guide produced by the Oak Ridge Safety program.

Both Oak Ridge and Hanford had major industrial and public safety programs during the war. This was not just a matter of responsibility (though there was that), but also because industrial accidents caused lost-time problems. The more accidents, the slower it would be until they had an atomic bomb ready to use. At Oak Ridge and Hanford, they claimed an exceptional occupational safety record — their injury rates were (they claimed) 62% below those of private industry. That still translated into 62 fatalities between 1943 and 1945 at the two sites, and a 3,879 disabling injuries. Given that those sites employed some 500,000 people between them, that means your chance of dying there was about one in ten thousand, while your chance of getting disablingly injured was more around one in a hundred.

Sometimes it takes a raw document like this, something a little off the beaten path to get you out of the well-worn narratives of this history. One knows of the criticality accidents, because they are unusual, and they are famous. But who knew of the child drowning? The janitor’s night out gone wrong? The carpenter crushed by a bulldozer? The accidental shooting of a bunkmate? Out of these little details, grim as they are, a whole social ecosystem falls out. It doesn’t have to supplant the traditional scientific story, which is still an important one. But it augments it, and makes it more human.