Posts Tagged ‘Edward Teller’

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The Spy, the Human Computer, and the H-bomb

Friday, August 23rd, 2013

One of the most enigmatic documents in early Cold War nuclear history is the so-called Fuchs-von Neumann patent. It was Los Alamos secret patent application number S-5292X, “Improvements in method and means for utilizing nuclear energy,” and dates from April 1946. It is mentioned, cryptically, often with heavy redaction, in many official histories of the hydrogen bomb, but also has recently surfaced as an object of historian’s speculation. The most obvious reason for its notoriety comes from its authors, but its importance  goes deeper than that.

The Los Alamos identification badges for Klaus Fuchs and John von Neumann. Courtesy of Los Alamos National Laboratory.

The Los Alamos identification badges for Klaus Fuchs and John von Neumann. Courtesy of Los Alamos National Laboratory.

The co-inventors were Klaus Fuchs and John von Neumann. Fuchs was a brilliant German physicist who was later exposed as the most important of the Soviet spies at Los Alamos. Von Neumann was a brilliant Hungarian mathematician and physicist, a “ringer” they brought in especially to help manage the explosive lens program, and is generally considered one of the smartest people in the 20th century. As one of the major contributors to the invention of modern computing, it was often remarked in his time that he was much smarter than the machines he was developing — he could do crazy-complicated math in his head without breaking a sweat. And he was a vehement anti-Communist at that — a man who spoke openly about the benefits of instigating thermonuclear war with the Soviets. So on the face of it, it’s an improbable match-up — the Soviet spy and the anti-Communist human computer. Of course, viewed in context, it’s not so improbable: they were both talented physicists, both worked at Los Alamos, and nobody at the lab knew Fuchs was a spy.

The patent is interesting to historians because it allegedly plays a key role in answering the (still quite murky) question of whether the Soviets got the H-bomb through espionage or by their own hard work. We know that Fuchs passed it on to the Soviets — the question is, what did it contain, and how did the Soviets use it? The reason it shows up recurrently is because the patent is allegedly one of the first suggestions of the concept of radiation implosion, that is, using the radiation output of a fission bomb as a means of initiating fusion. In 1951, this would become one of the central components of the so-called Teller-Ulam design of the hydrogen bomb, on which all subsequent hydrogen bombs were based.

Record of invention for the Fuchs-von Neumann design, "Improvements in Method and Means for Utilizing Nuclear Energy."

Record of Invention for the Fuchs-von Neumann design, “Improvements in Method and Means for Utilizing Nuclear Energy.” This copy is from the records of the Joint Committee on Atomic Energy in the Washington, DC, National Archives.

The contents of the patent itself is still officially secret in the United States. What is officially declassified  is little more than its title and some relevant dates — not much to go on. All descriptive aspects of it are totally classified. Which, generally speaking, makes it very hard to evaluate the aforementioned question of how useful it would have been to the Soviet Union, since we don’t officially know what is in it.

But in the last couple of years, things have changed on this latter point. The patent application is still classified in the United States.1 But the contents of the patent appear to have been declassified, and published, in Russia. I’ve talked a bit in the past about how the Russians have declassified a bunch of information about the American bomb project that they got from espionage, despite the fact that this information is still probably classified in the United States. It would be really, really wonderful to know the back-story on why they do this, and whether there is any discussion with American classification authorities before the Russians start releasing information about old American bomb designs. The book series in question is Atomni’ Proekt SSSR (USSR Atomic Project: Documents and Materials), which is cheerfully described on the inside as “intended for everybody interest in the history of the Soviet Atomic Project.” Indeed!

In this case, the late Herb York told me that the late German Goncharov, one of the editors of the Atomni’ Proekt SSSR series, approached him and told him somewhat informally that he thought this information should be declassified. York told me that he couldn’t really officially respond to Goncharov about this, but he showed it to some people in Livermore, but they weren’t very interested. Anyway, whatever the case, Goncharov apparently got the whole thing published in 2009 in volume 3, book 1 of the series.

Fuchs-von Neumann H-bomb design

The above image, supposedly the Fuchs-von Neumann concept, had appeared in a few other sources prior to that, but not with explanatory text. The only person who has published a serious analysis of it is the physicist and historian Jeremy Bernstein, who wrote about it in Physics in Perspective in 2010.2 At the time, Bernstein only had access to the diagram and its above legend, which was first seen in print in Gregg Herken’s Brotherhood of the Bomb. Bernstein’s caption of the above device (which he credits Carey Sublette for deciphering) is as follows:

The design for thermonuclear ignition that Klaus Fuchs turned over to his Soviet control in March 1948. The detonator (box) on the left represents a gun-type fission bomb consisting of a projectile and target of highly enriched uranium (71 kg of 70% pure U235), which when joined form a supercritical mass and produce an explosive chain reaction. The projectile is carried forward by its momentum, striking the beryllium-oxide (BeO) capsule on the right, which contains a liquid 50:50 D–T mixture, compressing it by a factor of about 3, as represented by the outer circle. The radiation produced in the fission bomb heats up the BeO capsule, producing completely ionized BeO gas, which exerts pressure on the completely ionized D–T gas, compressing the capsule further to an overall factor of about 10, as represented by the inner circle.

The interpretation is pretty good, considering the lack of additional source material! But the Russians have since released the entire document — including its original description of how it is meant to work, in the original English. Here is an excerpt:

The detonator is а fission bomb of the gun type. The active material is 71 kg of 40% pure U233 [sic].3 The plug (48.64 kg) sits in the projectile, which is shot bу the gun into the target, the remaining 22-24 kg sits in the target. The tamper is ВеО. The fission gadget has аn efficiency of 5% (calculated). The tamper, which is transparent for the radiation from the fission bomb, is surrounded bу an opaque shell which retains the radiation in the tamper and also shields the booster and main charge against radiation.  […]

The primer contains 346 gm of liquid D-Т in 50:50 mixture, situated in the tamper. It is first compressed bу the projectile to 3-fold density. This precompression may not bе necessary. As the tamper and primer аге heated bу the radiation, the primer is further compressed, possibly to 10-fold density. (Radiation transport equalises the temperature in primer and tamper, and gives therefore rise to а pressure differential.) The compression opens the “gap” for the ignition of the primer. The primer is likely to have а very high efficiency (~80 %) of energy release.

The booster beyond the radiation shield contains D with about 4% Т. It is ignited bу the neutrons from the primer. Beyond the booster is the main charge of pure D, а cylinder of about 30 сm radius to contain the neutrons and arbitrary length.

So what’s happening here is that the big piece of uranium is being shot against another piece. In the process, it rams into a bunch of fusion fuel (the 50:50 deuterium-tritium mixture), and just mechanically compresses it by a factor of 3. Just brute force. Then the fission bomb starts to detonate, using its radiation to ionize and heat the beryllium-oxide tamper. This causes it to ionize and blow off, compressing that 50:50 DT mixture, and starting a fusion reaction (they hope). This produces a huge number of neutrons, which then go and hit some more fusionable fuel (a DT mixture with only 4% tritium). The neutrons from this then go on to continue and ignite a final reservoir of pure deuterium “of arbitrary length.”

The report then estimates that with 1 cubic meter of deuterium, it would have a blast range of 5 miles, a flash burn range of 10 miles, and prompt gamma radiation for 2 miles. It’s not clear what values they mean exactly for those ranges (is blast 1 psi, 5 psi, 10 psi, 20 psi?), but playing with the NUKEMAP makes me think they are talking about something in the megaton range. For 10 tons of deuterium, it says: “Blast ~ 100 square miles, Flash burn to horizon оr 10,000 square miles if detonated high up. Radioactive poison, produced bу absorption of neutrons in suitable materials, could bе lethal over 100,000 square miles.” Which is something in the many tens of megatons.

So was this radiation implosion? Well, kind of. The design uses the radiation energy to blow up the tamper, basically, compressing some fusion fuel. That’s part of how the Teller-Ulam design would later work. But the entire thing is done in the context of the non-workable Classical Super — the idea that you can start a fusion reaction at one length of a column of fusionable material and it will propagate down the rest of it. Radiation implosion, here, is really just trying to get a better initial “spark” of energy to start the Classical Super reaction. This is very different from Teller-Ulam, where the complete implosion of the secondary is a key and fundamental aspect. All of which is to say, while this is a kind of radiation implosion (mixed in with a lot of other complicated things), it’s pretty far from what is required to make a working hydrogen bomb, because the Classical Super idea just doesn’t work. The fusion reaction of the sort proposed just can’t sustain itself. Even Fuchs and von Neumann appear to have only perceived the importance of their invention as reducing the amount of tritium needed versus other Classical Super designs.4

The "Classical Super" design from 1946. A gun-type design is surrounded by a beryllium oxide tamper. There is a tubealloy (depleted uranium) shield to keep radiation off of the fusion fuel. The idea is to ignite a fusion reaction in a D+T mixture, which then ignites fusion reactions in a pure D mixture of arbitrary length.

The unworkable “Classical Super” design from 1946. A gun-type design is surrounded by a beryllium oxide tamper. There is a tubealloy (depleted uranium) shield to keep radiation off of the fusion fuel. The idea is to ignite a fusion reaction in a D+T mixture, which then ignites fusion reactions in a pure D mixture of arbitrary length. The Fuchs-von Neumann device is, in effect, just an attempt make the initial ignition easier, and does not question the (faulty) underlying assumption about propagation of the fusion reaction.

So what did the Soviets do with this information? Other documents in the series give some indication of that, and I’ve included the full set here (warning: large PDF, 13.5 MB), although it is completely in Russian.

The 1948 intelligence data is identified as “Material No. 713.” It includes a brief, near verbatim summary (Document No. 32) by the physicist Yakov Terletsky (the same one who interviewed Bohr at Beria’s request), as well as a brief report by Terletsky explaining what this material gave them compared to previous information about the American H-bomb work (Document No. 33). The latter is interesting; they seem most interested in the new theoretical information about the conditions required for deuterium fusion than they are about the specifics of the designs given. The strongest phrase is one where Terletsky says that the intelligence information will help them get beyond general, theoretical calculations and move towards the actual design or construction of a ‘deuterium superbomb, and thus reduce the time required for the practical implementation of the superbomb idea.”5

Document No. 34 includes an order by Beria that Kurchatov and Vannikov be required to write analyses of the intelligence information, and that Khariton be consulted on the information. This was made just a few days after Terletsky’s report. Vannikov and Kurchatov’s analysis is included as Document 35. They seemed quite encouraged and interested in the intelligence, and claim it will help them a lot. Of note is that they in particular mention that, among the useful things in the document, they thought that “the ideas about the role of particles and photons in the transmission of the explosion to the deuterium are new.”6 So they do seem to have picked up on that, though it is again mixed into a lot of other details. They then used this material to propose that the USSR start a full-fledged Super program, along the lines of the unanswered questions (and even some of the answered ones) reflected in the intelligence information.

The end of Beria's April 1948 memo written as a result of the Fuchs intelligence, instructing that Khariton's opinion should be sought, especially with respects to the future work of the KB-11 (Arzamas-16) laboratory.

The end of Beria’s April 1948 memo written as a result of the Fuchs intelligence, instructing that Khariton’s opinion should be sought, especially with respects to the future work of the KB-11 (Arzamas-16) laboratory.

One thing that comes out in this as well is that the Soviet scientists at this point only had one other significant intelligence source related to the Super work, from late 1946 (Material No. 462, which I’ve uploaded here.) This appears to be a summary of the Super lectures that Enrico Fermi gave at Los Alamos, and is focused entirely on the Classical Super approach to the bomb, with many uncertainties. If these two caches were the only significant espionage they had on the American Super program before starting their own Super program, that’s pretty interesting in and of itself, and helps put some pretty strict limitations on what they would have gotten out of the data.

Looking at all this, even with the knowledge that there is probably a lot more to the story, I come away with the following conclusions. First, Bernstein is probably right when he says that the Fuchs-von Neumann approach wouldn’t have helped the Soviets very much in terms of arriving at the Teller-Ulam design. As he puts it:

Part of the irony of this story is that the unlikely collaborators, John von Neumann and Klaus Fuchs, produced a brilliant invention in 1946 that could have changed the whole course of the development of the hydrogen bomb, but was not fully understood until after the bomb had been successfully made.

I think perhaps this might go a little too far in praising radiation implosion — it is brilliant of a sort, but it is only one piece in the overall puzzle. The bigger issue on the road to the Teller-Ulam design was not so much the idea that the radiation could be used to transmit the energy, or even to implode the secondary, but getting away from the Classical Super notion of starting a small reaction that would then propagate onward. Indeed, the real breakthrough in the end appears to have been getting out of that mindset altogether. Ulam’s big idea was of total compression of the secondary by putting the whole thing in a “box,” which Teller then realized could be done more efficiently with radiation implosion. Radiation implosion is just a part of the overall mechanism, one which Ulam later insisted was actually not even required.

But my second, perhaps deeper conclusion is that this intelligence appears to have been much more important than has been previously thought. It didn’t give the Soviets the right idea of how to make an H-bomb. But it did seem to convince them that the Americans were taking this work very seriously, and making serious progress, and that they should set up their own dedicated H-bomb program as soon as possible. That’s a big deal, from an organizational standpoint, arguably a much bigger deal than the idea that it gave them some hint at the final design.

The Soviets were talking about a serious H-bomb program in 1948, before they had a fission bomb, and before USA was really committing itself to making a hydrogen bomb. In this sense, while it isn’t clear that this intelligence saved them any real time on the bomb, it did convince them it was worth spending time on. In the end, that was what produced their successful hydrogen bomb models, in the end. Not the intelligence itself, but the program spurred on by the intelligence. And so in that sense, Fuchs does have a very real role in the Soviet hydrogen bomb program, even if his specific ideas were not realized to be relevant until after the fact. Our focus on the importance of individual design secrets can lead us to underestimate the importance of programmatic and organizational decisions in weapons development.7 We tend to focus on the question of, “did this fact get transmitted, and was it appreciated?” But facts, by themselves, do not build bombs. What they can do, though, is inspire scientists to think that the bombs can and should be made, so that they start the laborious process of actually making them. If the Fuchs intelligence did have this result, then it was very important indeed.

Notes
  1. Note that it is, and probably will always be, an application. Secret patent applications cannot be granted until they are non-secret. And even then, the Atomic Energy Act of 1946 explicitly bans the patenting of atomic bombs. For the long, thrilling history of secret atomic patents, check out my page on them and my various articles on the history of the policy. []
  2. Jeremy Bernstein, “John von Neumann and Klaus Fuchs: an Unlikely Collaboration,” Physics in Perspective 12 (2010), 36-50. []
  3. The “detonator” description is very strange. For one thing, using only 40% enriched uranium (I am sure that the U-233 is a typo, because it is not in the Russian version, but the 40% is repeated in both) seems strange for 1946, and there is a marked difference between the specificity of one part of the gun-type design (48.64 kg) and the other (22-24 kg). This may be some kind of strange transcription error; the original drawing that the above diagram is based on says 22.36 kg. 5% efficiency is ridiculously high for such a description, too — “Little Boy” had about a 1% efficiency with 80% enriched uranium. If 5% of the U-235 in the “detonator” underwent fission, it would be around 24 kilotons in yield — somethings quite achievable by less speculative means. []
  4. The 1946 Record of Invention describes the object of the device as follows: “To provide an improved method and means for initiating a self-sustaining thermo-nuclear reaction which minimizes the amounts of materials employed.” (My emphasis.) When you compare this design with other Classical Super designs, it is clear, I think, that they are really trying to keep the amount of tritium down to a minimum, by starting the fusion with the heavy compression of a very small tritium-rich zone. Given that in 1946, the supply of tritium was minuscule, this would be a pretty appealing aspect of such a design. []
  5. “Материал #713а, в целом, позволяет перейти от общих теоретических расчетов к конструированию дейтериевой сверхбомбы и т[аким] о[бразом] сократить время, необходимое для практического осуществления идеи сверхбомбы.” []
  6. “Приведенные в материале #713а принципиальные соображения о роли трития в процессе передачи взрыва от запала из урана-235 к дейтерию, соображения о необходимости тщательного подбора мощности уранового запала и соображения о роли частиц и квантов при передаче взрыва дейтерию являются новыми.” []
  7. Michael Gordin makes this point excellently in his excellent Red Cloud at Dawn when discussing why the Smyth Report is actually a pretty important document for the Soviets: it didn’t give them any details about how to build a bomb, but it did tell them how to start a bomb-building research program. []
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George Gamow and the atomic bomb

Friday, January 18th, 2013

George Gamow stands out as a colorful physicist among a generation of colorful physicists. He was a known wit, a friend to many of the “golden generation” of physicists, and — on top of all that — was a Russian émigré who had made a dramatic defection from the Soviet Union during a Solvay Conference. He was also a well-known popularizer of science, authoring well over a dozen works of physics aimed at the general public, often illustrated with his own amusing little drawings. He was quite a card: who else adds a scientist’s name to a massively important paper just to make a silly pun?

George Gamow, laughing and smoking, probably ca. the 1950s. Photo from the AIP Emilio Segrè Visual Archives.

George Gamow, laughing and smoking, probably ca. the 1950s. Photo via the AIP Emilio Segrè Visual Archives.

(Later in life, he became a very difficult person to be around, on account of his alcoholism. It was this fact that made me a little surprised that there was a free wine bar sponsored in the name of George Gamow at a meeting of the History of Science Society a few years back.)

Gamow’s scientific interests were all over the place — he was completely uninterested in disciplinary boundaries — and he was enormously influential on his peers as a “program builder.”1  It’s a little-known fact that Edward Teller came up with the idea of using a solid core of plutonium in the implosion design — an intuition he had because of his work with Gamow on the molten, compressed iron core of the Earth.2 Gamow’s work on nucleosynthesis and the Big Bang was immensely important to the advancement of cosmological thinking. Incidentally, Gamow did not like the term “Big Bang,”  because it sounded too much like nukes. He later even had an excursion into molecular biology.

But during World War II, Gamow didn’t work on the atomic bomb, though he continued to work on nuclear physics. One of the most charming letters I’ve found in the archives was written by Gamow to Vannevar Bush on August 12, 1945. You will note, of course, that this comes just three days after the bombing of Nagasaki, and is the same day the Smyth Report was released. In a clear but stylized handwriting, with a touch of refugee’s English, Gamow wrote the following letter to Bush:3

Click image to view PDF.

Click image to view PDF.

Aug 12th, 1945
19 Thoreau Drive
Bethesda, Md.

Dear Dr. Bush,

I am writing to you because I think you are the best man to advice me what to do. As you know I was in no way connected with the project of “atomic bomb” developement, while on the other hand, working all my life on nuclear physics, I naturally could not help not thinking about it and have rather clear ideas about the possibilities involved etc. As long as the whole thing remained a supersecret I was naturally trying to hold all my thoughts to myself. However now, when the thing exploded and all the newspapers are full of informations, I wonder where the boundary between what can and what cannot be told should be placed. Thus, for example, in my course of nuclear physics which I am giving in G.W.U. this summer I will have to speak next week about nuclear transformations, thermonuclear reaction, and nuclear chain reactions. Should I entirely avoid mentioning explosive reactions or not?

Again, I am now preparing the new edition of my Book on Nuclear Physics for Oxford Univ. Press. How much could be told in it about this part of the problem? Finally I was recently asked to write a small popular book on Atomic Energy. Must I reject such offer or not?

You understand of course that in all these cases the question is not about the technical details which I do not know, but about broad “purely scientific” point of view. As the matter of fact I do not think I know much more on the subject that the scientists in other countries, as for example in Soviet Russia, know at present, so that such utterings on my part will hardly be of any particular use for the “competitors.” Still, I would not like to do anything in this direction, without first receiving your advice.

Hoping to hear from you soon

Your very truly G Gamow.

Gamow’s concern was not unique to him, though he was a little ahead of the curve when it came to expressing it. He, like most other physicists, quickly saw that nuclear physics was going to become a much more troublesome thing in the age of atomic bombs. One of the biggest concerns at the time, by those inside the bomb project and those not, was that if nuclear physics became a top-secret area, it would severely impact the education of new physicists.

His letter did not go unnoticed; Vannevar Bush wrote him back a careful reply two days later, pointing out that the Smyth Report was released at almost the same time that Gamow’s letter was written, and that one of its explicit purposes was to make that firm line of security visible to folks like Gamow. Bush then offered up this bit of speculation:

I have no doubt that later there will be constituted in some way an official body to determine the proper bounds of scientific discussion, and undoubtedly competent scientists will be present on any such body. How this may possibly be done it is too early to know. However, in the interim there is a guide in the form of a report [the Smyth Report] and after the body is established there will be a place to turn which anyone can use who may be in doubt. 

The reality was somewhat more complicated than this, in the end. Policing “the proper bounds of scientific discussion” was ostensibly the role of the Atomic Energy Commission, but they found it quite hard to do such a thing in practice.

Gamow was, in the end, somewhat sucked into the weapons complex. He was a lecturer to US Naval Officers on fission physics just before Operation Crossroads, and later he was involved in the work on the hydrogen bomb, at Los Alamos. While there he drew this rather unusual little drawing celebrating the discovery/invention of the Teller-Ulam design in 1951:4

Gamow's drawing of Ulam and Teller, March 1951

What does it mean? Stanislaw Ulam as a very Bugs-Bunnyish hare, Edward Teller as a tortoise? The most banal and boring interpretation would be that Teller had been working at the H-bomb problem for a long time, and it was Ulam — the relative new-comer — had scooped him.

But I can’t help but wonder if there is more to its imagery than that — Gamow’s pen was famously more quick-witted than that. Perhaps there is meant to be a secret clue as to the differences in their approaches?

One stab at it: Teller’s Classical Super involved a propagating thermonuclear reaction in a large mass of fusion fuel — you light one end of a deuterium candle, and the thermonuclear “fire” travels along it. Ulam’s compression scheme (which would be translated into radiation implosion in collaboration with Teller) involved trying to ignite the entire fusion fuel mass all at once, more or less. Teller’s approach is a much slower reaction than Ulam’s; this is part of the reason that Teller’s Classical Super wouldn’t work (the fuel cools too quickly and can’t sustain the temperatures needed for fusion). So Ulam is the fast rabbit, Teller is the slow turtle, and in this instance (unlike Aesop), the rabbit wins the race.

Or perhaps it has something to do with the different geometries? Why does the Teller turtle have three rocks? Is the carrot a reference to the relatively long geometry of the Ulam approach, versus the spherical symmetry of the Alarm Clock design? Is the “P” on Ulam’s hat for his native Poland, or something else?

Are there secrets hidden in Gamow’s humor? Might Gamow be having the last laugh?

Notes
  1. Nasser Zakariya, “Making Knowledge Whole: Genres of Synthesis and Grammars of Ignorance,” Historical Studies in the Natural Sciences 42, No. 5 (November 2012), 432-475. []
  2. Robert Christy usually gets the credit for the solid core. It was Teller’s initial idea, but it was Christy who proved it would work. []
  3. George Gamow to Vannevar Bush (12 August 1945), General Records of the Office of Scientific Research and Development, National Archives and Records Administration, RG 227, Box 110, “Security – S-1.” []
  4. This scan comes from the copy reproduced in Peter Galison’s Image and Logic. []
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Martian perspectives

Friday, September 28th, 2012

Of the four Hungarian “Martians” who worked the Manhattan Project — so known for their incomprehensible language, their European proclivities, and their exceptional intelligence — Leo Szilard and Edward Teller are tied, in my mind, as the most fascinating and intense personalities. (John von Neumann, the hawkish human computer, comes in a close second. Eugene Wigner, important as he was in the history of nuclear developments, just doesn’t compare to either of the other three when it comes to eccentricity.)

A rare photo of Szilard and Teller together. From a 1960 televised debate they participated in. Source.

Neither need much by means of an introduction on this blog, I don’t think. Leo Szilard was the guy who got the bomb project rolling, but quickly soured on military management. Edward Teller was the future father of the hydrogen bomb, among many other things.

Szilard was one of the strongest advocates of the idea that the atomic bomb should not first be used against an actual civilian target, but should be “demonstrated” in some way, such as on an island or a remote location. He had begun activity on this front as early as the summer of 1942, before the bomb project was truly under way.

His last attempt was a petition he circulated for scientists to sign, with the idea was that it would be presented to the President of the United States. It said, in part:1

We, the undersigned scientists, have been working in the field of atomic power. Until recently we have had to fear that the United States might be attacked by atomic bombs during this war and that her only defense might lie in a counterattack by the same means. Today, with the defeat of Germany, this danger is averted and we feel impelled to say what follows.

The war has to be brought speedily to a successful conclusions and attacks by atomic bombs may very well be an effective method of warfare. We feel, however, that such attacks on Japan could not be justified, at least not unless the terms which will be imposed after the war on Japan were made public in detail and Japan were given an opportunity to surrender.

If such public announcement gave assurance to the Japanese that they could look forward to a life devoted to peaceful pursuits in their homeland and if Japan still refused to surrender our nation might then, in certain circumstances, find itself forced to resort to use of atomic bombs. Such a step, however, ought not to be made at any time without seriously considering the moral responsibilities which are involved. The atomic bombs at our disposal represent only the first step in this direction, and there is almost no limit to the destructive power which will become available in the course of their future development. Thus a nation which sets the precedent of using these newly liberated forces of nature for purposes of destruction may have to bear the responsibility of opening the door to an era of devastation on an unimaginable scale.

The petition continued; you can read the full version here. It was apparently signed by “approximately sixty other scientists” at Chicago.

But Edward Teller was not one of those scientists who signed it.

Edward Teller and Gregory Breit, 1976. (Aside: Breit had been the head of bomb design physics on the Manhattan Project, and was the person who Oppenheimer replaced when he was brought in on the project.) Via the AIP Emilio Segrè Visual Archives.

To many, the idea that Teller would not oppose using the bombs would not be surprising. After all, he was the maker of megatons, right? But this is a misconception, in a sense. Teller was a sensitive soul. He spent a good part of the Cold War trying to argue that he would never have chosen to use the bombs if he had been given a chance. He insisted that his work on the bombs was solely to avoid nuclear war, not encourage it. He was not, I don’t feel, truly bloodthirsty.

Over the later course of his life, Teller occasionally argued that he had opposed the bombing of Hiroshima. This was, as the historian Robert Crease has pointed out, a “truthy” approach — a revisionism based on the history that Teller may have wanted to exist.2

But this is what Teller wrote to Szilard, in early July 1945, a few weeks before the Trinity test:3

Dear Szilard:

Since our discussion I have spent some time thinking about your objections to an immediate military use of the weapon we may produce. I decided to do nothing. I should like to tell you my reasons.

First of all let me say that I have no hope of clearing my conscience. The things we are working on are so terrible that no amount of protesting or fiddling with politics will save our souls.

This much is true: I have not worked on the project for a very selfish reason and I have gotten much more trouble than pleasure out of it. I worked because the problems interested me and I should have felt it a great restraint not to go ahead. I can not claim that I simply worked to do my duty. A sense of duty could keep me out of such work. It could not get me into the present kind of activity against my inclinations. If you should succeed in convincing me that your moral objections are valid, I should keep working. I hardly think that I should start protesting.

This is a strikingly honest way to discuss one’s motivations for working on weapons of mass destruction. Not because of duty — but because of curiosity. Teller worked on the bomb because he thought the bomb was interesting. He wanted to use the bomb because it was the ultimate fruition of that interest. That he could admit such a thing is actually pretty stunning. He did think, though, that morality could stop him from such a project — if he could be convinced.

Teller continued:

But I am not really convinced of your objections. I do not feel that there is any chance to outlaw any one weapon. If we have a slim chance of survival, it lies in the possibility to get rid of wars. The more decisive a weapon is the more surely it will be used in any real conflict and no agreements will help.

Our only hope is in getting the facts of our results before the people. This might help to convince everybody that the next war would be fatal. For this purpose actual combat-use might even be the best thing.

This is an interesting and perhaps not wholly predictable turn, if one subscribes only to a Strangelovian caricature of Teller. Szilard wanted Teller to agree that the bomb should not be used without warning. Teller in turn says that as a scientist who worked on the bomb, he had no responsibility for how it would be used — he was the maker of tools, not the user of them.

A picture of Edward Teller as he probably looked in the early 1940s. Date unknown. From the AIP Emilio Segrè Visual Archives, photo by Francis Simon.

What he felt a responsibility for was in informing people about the bomb, about its consequences, about the reason that it should be a weapon that ends all wars. And, as he argues, “for this purpose actual combat-use might even be the best thing.”

If his responsibility is to show the world what dangers lie ahead, what would be a better way for doing so that utterly destroying at least one city?

Teller concluded:

And this brings me to the main point. The accident that we worked out this dreadful thing should not give use the responsibility of having a voice in how it is to be used. This responsibility must in the end be shifted to the people as a whole and that can be done only by making the facts known. This is the only cause for which I feel entitled in doing something: the necessity of lifting the secrecy at least as far as the broad issues of our work are concerned. My understanding is that this will be done as soon as the military situation permits it.

All this may seem to you quite wrong. I should be glad if you showed this letter to Eugene [Wigner] and to [James] Franck who seem to agree with you rather than with me. I should like to have the advice of all of you whether you think it is a crime to continue this work. But I feel that I should do the wrong thing if I tried to say how to tie the little toe of the ghost to the bottle from which we just helped it to escape.

Teller’s “main point” was that the moral work of the scientists should begin just after the bomb was used. It should be to remove the secrecy and make the facts known, because their special knowledge of how bad things could get — and this is Edward Teller speaking, so we know he was pretty imaginative on this front — gave them the moral imperative to warn the world.4

Teller attempting to make himself understood, in 1963. Via the AIP Emilio Segrè Visual Archives.

In writing his memoirs, some five decades later, Teller noted that,

Rereading the letter, I cannot really agree with the person, my earlier incarnation, who wrote it. I stand fully behind my strong statement against secrecy, but I would no longer say that helping the “ghost” escape was terrible at all. That was our job as scientists, a point that became clearer when I became aware of the great progress that the Soviet Union had made on a nuclear explosive. The responsibility of scientists is to describe and demonstrate what is possible, to disseminate that knowledge as fully as possible, and, with everyone else in our democracy, to share the decisions that are necessarily connected with knowledge.5

Teller’s anti-secrecy stance may seem incongruous given his reputation for nuclear hawkishness. But for Teller, secrecy was something that slowed bomb innovation down — and bomb innovation was the ultimate goal. In such a light, an anti-secrecy hawk makes perfect sense, even if it goes against the conventional political mapping.

Returning to Szilard’s petition five decades later, Teller concluded three things:

First, Szilard was right. As scientists who worked on producing the bomb, we bore a special responsibility. Second, Oppenheimer was right. We did not know enough about the political situation to have a valid opinion. Third, what we should have done but failed to do was to work out the technical changes required for demonstrating the bomb over Tokyo and submit that information to President Truman.6

The first two are fairly straightforward positions, but the last is interesting and provocative. The Manhattan Project scientists spent a huge amount of time thinking up ways to make the bombs more deadly. Whether it was in racing towards a megaton age (Teller’s approach), or calculating the best way to kill Japanese firefighters (Penney’s approach), or — the subject of a future post — a proposal for generating radioactive thunderclouds (seriously), an enormous effort was put into making deadly weapons. Absolutely no technical effort was put into figuring out how one might use the bombs to end the war without bloodshed. The idea was proposed — even urged — but exactly zero effort was put into making it look like a realistic possibility.

The issues raised in this “Martian dialogue” didn’t go away after Hiroshima. If anything, they got more intense, more immediate. What is the responsibility of the tool-maker for his or her tools? What is the responsibility of the scientist to the public? Szilard chose his path and never strayed from it — he never made another weapon again. Teller, if anything, became more extreme on his own path, becoming synonymous with the scientist co-opted by the military-industrial complex, and not just a touch of self-delusion.

Notes
  1. Leo Szilard, “Petition to the President of the United States,” (17 July 1945), copy in Harrison-Bundy Files Relating to the Development of the Atomic Bomb, 1942-1946, microfilm publication M1108 (Washington, D.C.: National Archives and Records Administration, 1980), Roll 6, Target 5, Folder 76, “Interim Comittee — Scientific Panel.” []
  2. Robert P. Crease, “Biography: Envy and Power,” Nature 468 (2 December 2010), 629-630. []
  3. Edward Teller to Leo Szilard (2 July 1945), copy in the J. Robert Oppenheimer papers (MS35188), Library of Congress, Washington, DC, Box 71, Folder, “Teller, Edward, 1942-1963.” []
  4. Teller forwarded a copy of this letter to J. Robert Oppenheimer, of all people. He prefaced it with a hand-written note, scrawled in an elegant, old-world calligraphy. “What I say is, I believe, in agreement with your views,” he wrote. “At least in the main points.” []
  5. Edward Teller with Judith Schoolery, Memoirs: A Twentieth Century Journey in Science and Politics (Cambridge, Mass.: Perseus Books, 2001), 208. []
  6. Teller, Memoirs, 206. []
Redactions

In Search of a Bigger Boom

Wednesday, September 12th, 2012

The scientist Edward Teller, according to one account, kept a blackboard in his office at Los Alamos during World War II with a list of hypothetical nuclear weapons on it. The last item on his list was the largest one he could imagine. The method of “delivery” — weapon-designer jargon for how you get your bomb from here to there, the target — was listed as “Backyard.” As the scientist who related this anecdote explained, “since that particular design would probably kill everyone on Earth, there was no use carting it anywhere.”1

Edward Teller looking particularly Strangelovian. Via the Emilio Segrè Visual Archives, John Wheeler collection.

Teller was an inventive, creative person when it came to imagining new and previously unheard-of weapons. Not all of his ideas panned out, of course, but he rarely let that stop his enthusiasms for them. He was seemingly always in search of a bigger boom. During the Manhattan Project, he quickly tired of working on the “regular” atomic bomb — it just seemed too easy, a problem of engineering, not physics. From as early as 1942 he became obsessed with the idea of a Super bomb — the hydrogen bomb — a weapon of theoretically endless power.

(One side-effect of this at Los Alamos is that Teller passed much of his assigned work on the atomic bomb off to a subordinate: Klaus Fuchs.)

It took over a decade for the hydrogen bomb to come into existence. The reasons for the delay were technical as well as interpersonal. In short, though, Teller’s initial plan — a bomb where you could just ignite an arbitrarily long candle of fusion fuel — wouldn’t work, but it was hard to show that it wouldn’t work. Shortly after abandoning that idea more or less completely, Teller, with the spur from Stan Ulam, came up with a new design.

The Teller-Ulam design allows you to link bombs to bombs to bomb. John Wheeler apparently dubbed this a “sausage” model, because of all of the links. Ted Taylor recounted that from very early on, it was clear you could have theoretically “an infinite number” of sub-bombs connected to make one giant bomb.

A few selected frames from Chuck Hansen’s diagram about multi-stage hydrogen bombs, from his U.S. Nuclear Weapons: A Secret History. Drawing by Mike Wagnon.

The largest nuclear bomb ever detonated as the so-called “Tsar Bomba” of the Soviet Union. On 1961, it was exploded off the island of Novaya Zemlya, well within the Arctic Circle. It had an explosive equivalent to 50 million tons of TNT (megatons). It was only detonated at half-power — the full-sized version would have been 100 megatons. It is thought to have been a three-stage bomb. By contrast, the the largest US bomb ever detonated was at the Castle BRAVO test in 1954, with 15 megatons yield. It was apparently “only” a two-stage bomb.

The dropping of the Tsar Bomba, 1961: an H-bomb the size of a school bus.

We usually talk about the Tsar Bomba as if it represented the absolute biggest boom ever contemplated, and a product of unique Soviet circumstances. We also talk about as if its giant size was completely impractical. Both of these notions are somewhat misleading:

1. The initial estimate for the explosive force of the Super bomb being contemplated during World War II was one equivalent to 100 million tons of TNT. As James Conant wrote to Vannevar Bush in 1944:

It seems that the possibility of inciting a thermonuclear reaction involving heavy hydrogen is somewhat less now than appeared at first sight two years ago. I had an hour’s talk on this subject by the leading theoretical man at [Los Alamos]. The most hopeful procedure is to use tritium (the radioactive isotope of hydrogen made in a pile) as a sort of booster in the reaction, the fission bomb being used as the detonator and the reaction involving the atoms of liquid deuterium being the prime explosive. Such a gadget should produce an explosion equivalent to 100,000,000 tons of TNT.2

Teller was aiming for a Tsar Bomba from the very beginning. Whether they would have supported dropping such a weapon on Hiroshima, were it available, is something worth contemplating.

2. Both the US and the USSR looked into designing 100 megaton warheads that would fit onto ICBMs. The fact that the Tsar Bomba was so large doesn’t mean that such a design had to be so large. (Or that being large necessarily would keep it from being put on the tip of a giant missile.) Neither went forward with these.

A US MK 41 hydrogen bomb.

But remember that the original Tsar Bomba was actually tested at 50 megatons, which was bad enough, right? Both the US and the Soviet Union fielded warheads with maximum yields of 25 megatons. The US Mk-41, of which some 500 were produced, and the Soviet  SS-18 Mod 2 missiles were pretty big booms for everyday use. (The qualitative differences between a 50 megaton weapon and a 25 megaton weapon aren’t that large, because the effects are volumetric.)

3. Far larger weapons were contemplated. By who else? Our friend Edward Teller.

In the summer of 1954, representatives from Los Alamos and the new Livermore lab met with the General Advisory Committee to the U.S. Atomic Energy Commission. Operation Castle had just been conducted and had proven two things: 1. very large (10-15 megaton or so), deliverable hydrogen bombs could be produced with dry fusion fuel; 2. Livermore still couldn’t design successful nuclear weapons.

Norris Bradbury, director of Los Alamos, gave the GAC a little rant on the US’s current “philosophy of weapon design.” The problem, Bradbury argued, was that the US had an attitude of “we don’t know what we want to do but want to be able to do anything.” This was, he felt, “no longer relevant or appropriate.” The answer would be to get very definite specifications as to exactly what kinds of weapons would be most useful for military purposes and to just mass produce a lot of them. He figured that the strategic end of the nuclear scale had been pretty much fleshed out — if you can routinely make easily deliverable warheads with a 3 megaton yield, what else do you need? All diversification, he argued, should be on the lower end of the spectrum: tactical nuclear weapons.

Edward Teller and Enrico Fermi, 1951. Courtesy of the Emilio Segrè Visual Archives.

When Teller met with the GAC, he also pushed for smaller bombs, but he thought there was still plenty of room on the high end of the scale. To be fair, Teller was probably feeling somewhat wounded: Livermore’s one H-bomb design at Castle had been a dud, and the AEC had cancelled another one of his designs that was based on the same principle. So he did what only Edward Teller could do: he tried to raise the ante, to be the bold idea man. Cancel my H-bomb? How about this: he proposed a 10,000 megaton design.

Which is to say, a 10 gigaton design. Which is to say, a bomb that would detonate with an explosive power some 670,000 times the bomb that was dropped on Hiroshima.3

If he was trying to shock the GAC, it worked. From the minutes of the meeting:

Dr. Fisk said he felt the Committee could endorse [Livermore’s] small weapon program. He was concerned, however, about Dr. Teller’s 10,000 MT gadget and wondered what fraction of the Laboratory’s effort was being expended on the [deleted]. Mr. Whitman had been shocked by the thought of a 10,000 MT; it would contaminate the earth.4

The “deleted” portion above is probably the names of two of the devices proposed — according to Chuck Hansen, these were GNOMON and SUNDIAL. Things that cast shadows.

The Chairman of the GAC at this time, I.I. Rabi, was no Teller fan (he is reported to have said that “it would have been a better world without Teller”), and no fan of big bombs just for the sake of them. His reaction to Teller’s 10 gigaton proposal?

Dr. Rabi’s reaction was that the talk about this device was an advertising stunt, and not to be taken too seriously.

Don’t listen to Teller, he’s just trying to rile you. Edward Teller: trolling the GAC. A 10,000 megaton weapon, by my estimation, would be powerful enough to set all of New England on fire. Or most of California. Or all of the UK and Ireland. Or all of France. Or all of Germany. Or both North and South Korea. And so on.

“Don’t Fence My Baby In.” Cartoon by Bill Mauldin, Chicago Sun-Times, 1963.

In 1949, Rabi had, along with Enrico Fermi, written up a Minority Annex to the GAC’s report recommending against the creation of the hydrogen bomb. The crux of their argument was thus:

Let it be clearly realized that this is a super weapon; it is in a totally different category from an atomic bomb. The reason for developing such super bombs would be to have the capacity to devastate a vast area with a single bomb. Its use would involve a decision to slaughter a vast number of civilians. We are alarmed as to the possible global effects of the radioactivity generated by the explosion of a few super bombs of conceivable magnitude. If super bombs will work at all, there is no inherent limit in the destructive power that may be attained with them. Therefore, a super bomb might become a weapon of genocide.

If that doesn’t apply to a 10,000 megaton bomb, what does it apply to?

Was Teller serious about the 10 gigaton design? I asked a scientist who worked with Teller back in the day and knew him well. His take: “I don’t doubt that Teller was serious about the 10,000 MT bomb. Until the next enthusiasm took over.” In this sense, perhaps Rabi was right: if we don’t encourage him, he’ll move on to something else. Like hydrogen bombs small enough to fit onto submarine-launched missiles, for example.

It’s hard not to wonder what motivates a man to make bigger and bigger and bigger bombs. Was it a genuine feeling that it would increase American or world security? Or was it just ambition? I’m inclined to see it as the latter, personally: a desire to push the envelope, to push for the bigger impact, the biggest boom — even into the territory of the dangerously absurd, the realm of self-parody.

Notes
  1. Robert Serber, The Los Alamos primer: The first lectures on how to build an atomic bomb (Berkeley: University of California Press, 1992), page 4, fn. 2. []
  2. Letter dated October 20, 1944 from James B. Conant to Vannevar Bush, Subject: Possibilities of a Super Bomb. Vannevar Bush-James B. Conant Files, Records of the Office of Scientific Research & Development, S-1, NARA, Record Group 227, folder 3. Quoted from Chuck Hansen, The swords of Armageddon: U.S. nuclear weapons development since 1945 (Sunnyvale, Calif.: Chukelea Publications, 1995), III-17. []
  3. Actually, if you take the Hiroshima yield to be 15 kilotons, it comes out to a nice round 666,666 times the strength of the Hiroshima bomb. But the precision there seemed arbitrary and the symbolism seemed distracting, so I’m relegating this to just a footnote. []
  4. Minutes of the Forty-First Meeting of the General Advisory Committee to the U.S. Atomic Energy Commission, July 12-15, 1954, on p. 55. []
Redactions

James B. Conant on Trinity (1945)

Monday, July 16th, 2012

This week, you’ll get your weekly document on a Monday, because it’s a special occasion. Today, July 16, 2012, is the 67th anniversary of the first test of an atomic bomb: “Trinity.” 

A photo negative from the first milliseconds of the nuclear age. The bright spots are where the negative was burnt through by the heat. Photo by Berlyn Brixner; scanned from the National Archives Still Pictures Branch, 454-RF-12A (TR84-1).

A lot has been written about “Trinity.” What I thought I’d offer up is a perspective on the test that you’ve probably never seen — the personal account of James B. Conant, President of Harvard and key figure in the Manhattan Project.

The original document isn’t easy to come by — it was withdrawn from the Bush-Conant File when it was microfilmed — but James Hershberg, when writing his great Conant biography (James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age) managed to get access to it, where it is reprinted as an appendix. It’s one of the more gripping of the many personal accounts of the first bomb test, and as far as I’ve seen, isn’t posted anywhere else on the web.

James B. Conant (fourth from left) at a meeting with Uranium Committee principles at UC Berkeley, March 1940. Left to right: Ernest O. Lawrence, Arthur C. Compton, Vannevar Bush, Conant, Karl Compton, Alfred L. Loomis.

This transcription is Hershberg’s; the original is no doubt in Conant’s impossible handwriting. Any notes italicized in brackets are Hershberg’s, any not-italicized are mine.1

Rather than breaking it up with comments, I’ve added footnotes to highlight little points or add a little depth to things that you might not be familiar with, unless you are a serious Manhattan Project nerd. The footnotes are only visible if you look at this post in “single post” mode, rather than via the main site’s front page. If you don’t see any footnotes, click on the title of this post at the top. The bolding is by me. Any non sic‘d typos are probably by me, too!

Conant and Bush reenact a post-Trinity handshake for the “March of Time” documentary on the atomic bomb. Apparently they were really just in a Boston garage for the reenactment. Via the New York Times.


Notes on the “Trinity” Test Held at Alamogordo Bombing Range


125 miles south east of Alburquerque

5:30 a.m. Monday, July 16

V. Bush, Gen. Groves, and J.B.C. arrived at the Base Camp located 10 miles from the bomb at about 8 p.m. Sunday evening. After dinner at the mess and some brief explanation by [J.R.] Oppenheimer, [R.C.] Tolman, [G.] Kistiakowsky, and [I.I.] Rabbi [sic] in very informal conversation we went to bed. The atmosphere was a bit tense as might be expected but everyone felt confident that the bomb would explode. The pool on the size of the explosion ran from 0 (a few pessimists) to 18,000 (Rabbi [sic]) and perhaps someone at 50,000 [several words censored].2 My own figure was 4400 [tons of T.N.T.] but I never signed up.3 It was a bad night though the weather forecast had been favorable for a clear early morning with light winds (the desired condition). From about 10:30 to 1 a.m., it blew very hard thus preventing sleep in our tent and promising a postponement of the Test. Then it poured for about an hour!

At 1 a.m. General Groves arose and went out to the forward barricade with the key personnel. There were two forward bases located 10,000 yds. N. & S. of the bomb. The [wiring?] from [this?] point to the test and to the camp was fantastic in the [extreme?].4 The instrumentation of the test included a vast array of equipment. At 3:15 a.m., the rain having just ceased, Rabbi [sic]5 came into our tent (V. Bush and JBC) and said that there had been much talk of a postponement because of the weather but reports indicated a 75% chance of going through with it but at 5 a.m. instead of the scheduled 4 a.m.

We got up & dressed and drank some coffee about 4 a.m. and wandered around. The sky was still overcast. It had not rained however at the zero point (the bomb)6 and the [wires? lines?] were O.K. Word then came through about 4:30 that 5:10 would be the time. About 5 p.m. [sic a.m.] or a little after, word came that the firing would occur at 5:30. Shortly after, General Groves came back to the forward area. We prepared to view the scene from a slight rise near the camp. Col. S[tafford]. Warren [was] in charge of health.7 Tolman, Rabbi [sic], Gen. Groves & J.B.C. were more or less together.8 It was agreed that because of the expected (or hoped!) bright flash and the ultra violet light (no ozone to absorb it) it would be advisable to lie flat and look away at the start, then look through the heavy dark glass.

At 5:20 the sirens blew the 10 min signal then another at 5:25 and I think another 2 mins. before. We lay belly down facing 180 [degrees] away from the spot on the tarpaulin. I kept my eyes open looking at the horizon opposite the spot. It was beginning to be light, but the general sky was still dark particularly in the general direction I was looking. Through the loud speaker nearby I heard [Samuel] Allison counting the seconds minus 45, minus 40, minus 30, minus 20, minus 10. (The firing was done by some kind of timing devices started at minus 45 sec.) These were long seconds! Then came a burst of white light that seemed to fill the sky and seemed to last for seconds. I had expected a relatively quick and bright flash. The enormity of the light and its length quite stunned me. My instantaneous reaction was that something had gone wrong and that the thermal nuclear transformational of the atmosphere, once discussed as a possibility and jokingly referred to a few minutes earlier, had actually occurred.9  Slightly blinded for a second, I turned on my back as quickly as possible and raising my head slightly, could see the “fire” through the dark glass. At that stage it looked like an enormous pyrotechnic display with great boiling of luminous vapors, some spots being brighter than others. A picture from memory is as seen through heavy dark glass.

Trinity fireball drawing by James Conant

Very shortly this view began to fade and without thinking the glass was lowered and the scene viewed with the naked eye. The ball of gas was enlarging rapidly and turning into a mushroom. It was reddish purple and against the early dawn very luminous, though I instantly thought of it as colored [somewhere?]. Then someone shouted watch out for the detonation wave (this was 40 sec after zero time). Still on my back I heard the detonation but was not in a position to notice any blast (there was relatively little felt here). The sound was less loud or startling than I expected, but the shock of sensory impression was still dominant in my mind. Then I got up and watched the spread of the colored luminous gas. There was two secondary explosions, after the detonation wave reached us or just before. The cloud billowed upward when these occurred and very soon thereafter [billowed?] up as would an oil fire, the color became [illegible] and the whole looked more like a [unintelligible] fire (though on an enormous scale). The column of smoke then began to spread and took on a Z form which persisted for some time. The spectacular part must have been confined to about 90 seconds. The phases observed by the eve were as follows from memory.

Conant's drawing of the rising and dissipating mushroom cloud

As soon as I had lowered my dark glass and before rising I shook Gen. Groves hand who said “Well, I guess there is something in nucleonics after all.”10 Tolman as we rose said, that is something very different from the 100-ton TNT shot,11 “entirely differently, there is no question but what they got a nuclear reaction.” Then several people began saying, “Very much larger than expected. Rabbi [sic] said it was 15,000 Tons equivalent at least.”

At about 60 sec. as the cloud billowed up, the assembled group including many MPs’ gave out a spontaneous cheer.

Then the reports began to come in. Oppenheimer arrived in about 5 or 10 minutes and said the equivalent was 2100 Tons which was greeted with great skepticism. It afterwards turned out he had made an error in converting the first blast measurement and the figure showed 7,000 tons.12

The most exciting news was that the steel tower over “Jumbo” 800 yards away had disappeared.13 This was reported by some one with a telescope and verified by all. This was unexpected and showed a very much more powerful effect than expected.

Before we left at noon, the best estimate seemed to be between 10,000–15,000 though Rabbi [sic] maintain 18,000 would yet prove right.14 Careful exploration of the crater showed 1200 yards again more than expected. The toxicity problem proved not serious. Thought at 10,000 [yards] North evacuated in a hurry as their meter went off the scale almost at once and the cloud of smoke seemed to chase them they declared!15 All evacuation was by car, of course. One man at the Camp Site who looked at the explosion without dark eye glasses got a bad eye burn and was given morphine: the prognosis was that he would not lose his sight. G. Kistiakowsky, all [word illegible], came in to report that the shock wave had knocked him down as he stood outside the barricade at 10,000 S.16 There were reports of two others being knocked down at the same spot.

My first impression remains the most vivid, a cosmic phenomena like an eclipse. The whole sky suddenly full of white light like the end of the world. Perhaps my impression was only premature on a time scale of years!

J.B. Conant, Washington, D.C.
July 17, 1945 4:30 p.m.

Notes
  1. Citation: James B. Conant, “Notes on the ‘Trinity’ Test,” (17 July 1945), Bush-Conant File Relating the Development of the Atomic Bomb, 1940-1945, Records of the Office of Scientific Research and Development, RG 227, microfilm publication M1392, National Archives and Records Administration, Washington, D.C., n.d. (ca. 1990), Roll 5, Target 8, Folder 38, “Bush, V. 1944-45.” Reprinted in James Hershberg, James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age(New York: Knopf, 1993), 758-760. []
  2. The yield estimates are questions of how efficient the fission reaction will be — how much plutonium would fission before the bomb blew itself apart? This itself was a question of how effectively the implosion mechanism worked, and how long the bomb could be held in a supercritical state before full explosion. A rough estimate provided by Richard Garwin is that the complete fissioning of 1 kg of Pu-239 produces 17 kt of yield. The “Gadget” contained  6.2 kg of Pu-239 in its core. So obviously zero yield would mean no significant fissioning at all. 18 kt would mean only 17% of the plutonium fissioned. 50 kt would mean 47% fissioned. Conant’s estimate, 4.4 kt, would mean 4% fissioned. Perfect efficiency — 100% fissioning — would have been 105 kt. Separately, one wonders what Conant would have to say here that would still be censored today. I suspect it has does have something to do with efficiency questions, and his reasoning on them, because those were considered quite taboo by redactors until relatively recently. I suspect if this was re-reviewed by a classification officer today these lines would be cleared. Note that Rabi’s guess was in fact not chosen because of any optimism — he arrived late and it was the only figure left to choose! []
  3. Conant’s estimate looks low today — since we know that the bomb was 18 kt was correct. But for the first test, of course, there was no real barometer. The original estimates for the atomic bomb’s yield were much, much lower than what the bombs turned out to be — when Roosevelt signed off on the Manhattan Project in 1942, it was under the assumption that the first atomic bomb would be only 2 kt in yield! []
  4. These parenthetical sentences are from Hershberg and are likely good interpretations of Conant’s awful handwriting. []
  5. Conant consistently misspells I.I. Rabi’s name. But it is amusing to imagine two New England Yankees like Bush and Conant being visited by a rabbi for the Trinity test. []
  6. “Zero point” was the term for where the bomb was located, sometimes just called “Zero” or, eventually, “Ground Zero.” This was the original usage of the term, well before it became more commonly used for all manner of targets. The zero obviously came from marking out the distances from the bomb blast site — zero would have been the exact site of the bomb exploding. []
  7. Warren was in charge of making sure that nobody got too much radiation exposure at Trinity, especially from fallout. They actually did have a fallout scare, but more on that another time. []
  8. It’s interesting that Rabi was in this group and not any other. Tolman was Groves’ personal scientific advisor; Conant and Bush were high-level policy guys; Rabi was more or less just visiting — he wasn’t heavily involved in the bomb project, just a consultant, and was spending most of his time working on radar at MIT. It may have been his “outsider” status that got him put into the high-policy bunker. Or maybe Bush and Conant just liked him. I don’t know. []
  9. The idea that an atomic bomb might start a thermonuclear reaction in the atmosphere was not quite so seriously considered as a threat as it was later made out to be — and was something that was known to be physically impossible — but it’s not surprising that this unlikely fear came back to Conant in this instant of awe. It’s also worth remembering that nobody had seen an atomic bomb before, so this must have been fantastically more impressive even than later tests, when you had a general idea of what it ought to look like. I’m also reminded of a comment that Harold Agnew made about watching the first hydrogen bomb explosion in 1952, how it kept getting hotter, and hotter, and hotter, and he actually started to get worried that it would never stop. []
  10. “Nucleonics” was a term coined during World War II to designate the field of nuclear technology. It didn’t really catch on. []
  11. The 100-ton TNT shot was a detonation of isotope-laced explosives on May 7, 1945, done as a means of trying to calibrate instrumentation and expectations for the Trinity shot. Read more about it on Carey Sublette’s page. []
  12. Oppenheimer was regarded by all as quite brilliant when it came to the physics of these sorts of things, but poor when it came to the mathematics. But I don’t know that he actually did these equations — it’s unlikely. It’s still interesting that the revised estimate was off by 250%. Still, it was an estimate some 15 minutes after the first test, so let’s cut them some slack. []
  13. “Jumbo” was a massive containment unit that was initially supposed to have the bomb detonated inside of it, so that if it fizzled, the billion-dollars-worth of plutonium would be recoverable. It was not used, however. Details about Jumbo are here. Jumbo itself survived the blast, though its tower was destroyed. []
  14. And Rabi was, indeed, more or less correct — the final yield was just shy of 19 kt. But, again, he chose 18 kt not because he had any good reason to — he did it because it was the only choice left when he showed up. Now an historical question that I’ve never seen the answer to is how much money did Rabi win? Apparently it was only a $1 entry fee, and it was restricted to senior scientists, so it probably wasn’t much. We know that Oppenheimer (0.3 kt), Teller (45 kt), Kistiakowsky (1.4 kt), Bethe (8 kt), and Ramsey (zero) put in. So that’s at least 5 dollars, not counting the one Rabi would have gotten back for admission. (Note that Conant said he did not participate in the pool.) But it must have been more crowded a field than that, given that 18 kt was all that was left to Rabi when he arrived later, and it seems rather arbitrary given the other numbers listed. It may yet be an unsolved mystery… []
  15. This is related to the fallout scare that I mentioned previously — they were somewhat woefully underprepared for fallout issues, though they were aware they might exist. I have a post on this coming up fairly soon… []
  16. So I guess the drawings I posted here weren’t completely far-fetched! []