Posts Tagged ‘Leo Szilard’


When did the Allies know there wasn’t a German bomb?

Friday, November 13th, 2015

Fears of a German nuclear weapons program were the initial motivating concerns behind pushes in both the United States and the United Kingdom. Leo Szilard and Albert Einstein in the United States, and Otto Frisch and Rudolf Peierls in the United Kingdom, among others, were worried sick of the prospect of a Nazi atomic bomb. That these scientists were European émigrés of Jewish descent played no small role in their fears.

Diagram (left) and replica (right) of the Haigerloch reactor that Heisenberg and his team were trying to complete by the end of the war. Source: diagram is from Walker's German National Socialism and the Quest for Nuclear Power, 1939-1949, replica photo is from Wikipedia.

Diagram (left) and replica (right) of the  Haigerloch heavy-water moderated reactor that Heisenberg and his team were trying to complete by the end of the war. The cubes are of unenriched uranium metal. Source: The diagram is from Walker’s German National Socialism and the Quest for Nuclear Power, 1939-1949, the replica photo is from Wikipedia.

But eventually we came to find that the German atomic bomb project was stillborn. The Germans had a modest atomic power project, researching nuclear reactors, but were in no great rush for an atomic bomb. Of course, they are not necessarily unrelated projects — you can use nuclear reactors to produce plutonium. But it would require a much greater effort to do so than the Germans were engaged in. By any metric, the Germans were involved in a research program, not a production program. Their work was relatively small-scale, not a crash effort to get weaponized results.1

When did Manhattan Project officials know that the German program was not a serious threat, though? That is, when did they know that there was virtually no likelihood that the Germans would develop an atomic bomb in time for use in World War II? This is a question I get a lot, and a question that comes up in this season of Manhattan as well. It’s an important and interesting question, because it marks, in part, the transition from the Anglo-American bomb project from being an originally defensive project (making an atomic bomb as a deterrent against a German bomb) to an offensive one (making a bomb as a first-strike weapon against another non-nuclear country, Japan).

What makes this a tricky question to answer is that the word “know” is more problematic than it might at first seem. Historians of science in particular, because we are historians of knowledge, are quite aware of the ways in which “knowing” is less of a binary state than it might at first appear. That is, we are ordinarily accustomed to talk about “knowing” as if it were a simple case of yes or no — “they knew it or they didn’t.” But knowledge often is more murky than that, a gradient of possibilities. One might have suspicions, but not be sure. The amount of uncertainty can vary in all knowledge, and sometimes be deliberately encouraged or exaggerated to create a space for action or inaction. One’s knowledge can be incomplete or partially incorrect. And there are many different “levels” of knowledge — one might “know” that the Germans were working on reactors, but not know to what ends they were intending to use them.

Allied troops disassembling the German experimental research reactor at Haigerloch, as part of the Alsos mission. Source: Wikipedia.

Allied troops disassembling the German experimental research reactor at Haigerloch, as part of the Alsos mission. Source: Wikipedia.

At one end of the “knowledge” question, we can point to the success of the Alsos mission. Alsos (Greek for “Groves”) was an effort in which Allied scientific and intelligence officers moved into German sites along with the invading troops, seizing materials, facilities, and even scientists (the latter being eventually detained at Farm Hall). By November 1944, Samuel Goudsmit, the scientific leader of the Alsos mission, had concluded that the German program appeared stillborn. By the spring of 1945, of course, they had made sufficient progress into Germany to know for sure. So that is a definite back-end on when they “knew” that the Germans had no bomb.2

But what did they know before that? At what point did the Germans stop being the fear that they had once been? This is the far more interesting, trickier question.

Among the American scientists, the fears of a German bomb peaked sometime in mid-1942. This, not coincidentally, is exactly when the Americans decided to accelerate their program from the research phase into the production phase: when their work changed from thinking about whether atomic bombs were possible to actually trying to build them. As the Americans became more convinced that atomic bombs were feasible to build in the short-term, they became more worried that the Germans were actually building them, and might have started building them earlier than the Americans. Arthur Compton, Nobel Prize winning physicist and head of the University of Chicago Metallurgical Laboratory, wrote several particularly impassioned memos in the summer of 1942, urging an acceleration of atomic work largely out of fears of a German bomb:

We have recently become aware that the threat of German fission bombs is even more imminent than we supposed… If the Germans know what we know — and we dare not discount their knowledge — they should be dropping fission bombs on us in 1943, a year before our bombs are planned to be ready.”3

Compton’s fears appear genuine, and rest on the conservative assumption that the Germans were just as smart, and just as aware of the possibilities, as the Americans. (And we know that they were, in fact, aware of all of these possibilities at the exact same time — but the Germans judged the effort more difficult, and more risky, than the Americans did.) There is no other basis for Compton’s assumptions, as he had no access to intelligence information on German efforts (and, indeed, his memo calls for more work in that field). But they were also self-serving, because they encouraged more effort towards his own goal, which was to accelerate the American bomb program. Compton was not at all alone in these fears; Harold Urey, James Conant, and Ernest Lawrence were all quick to point out that the American effort had been relatively slow to start, and that the Germans had clever scientists who ought not be underestimated.

The palpable fears of Arthur Compton, June 1942.

The palpable fears of Arthur Compton, June 1942.

Up until 1942, these fears were not, arguably, unwarranted. The Germans and the Americans were in similar positions. But, in a touch of irony, at the moment the Americans decided to switch towards developing a workable bomb, the Germans instead were deciding that they no longer needed to prioritize the program. They had concluded it would be an immense effort that they could ill afford to undertake, and that it was extremely unlikely that the Americans (or anyone else) would find success in that field.

So when did the picture change with regards to US knowledge, and who was told? Over the course of 1943 and 1944, more and more intelligence was gathered that, added up, began to suggest that the Germans did not have much of a project. In late 1943, General Leslie Groves appointed a specific intelligence group to try and suss out information about the enemy’s work. One of their avenues of approach was better collaboration with the intelligence services of the United Kingdom, who had far better networks both in Germany and in neutral countries than did the Americans. They even had a spy within Germany, the Austrian chemist Paul Rosbaud, who worked at Springer-Verlag, the scientific publisher. By the end of 1943, the British had concluded that the German program was not going anywhere. They were able to account for Heisenberg’s movements all too easily, and there seemed to be no efforts to industrialize the work on the scale necessary to produce concrete results in the timescale of the war. This information was duly passed on to the Manhattan Project intelligence services.4

Did it have any effect? Not immediately. The Americans were not entirely sure whether the British assessments were accurate. As Groves put it in a memo to Field Marshall John Dill in early 1944:

We agree that the use of a TA [“Tubealloys” = atomic] weapon is unlikely. The indirect and negative evidence developed by your agencies to date is in support of this conclusion. But we also feel that as long as definite possibilities exist which question the correctness of this opinion in its entirety or in part we cannot afford to accept it as a final conclusion. Repeated reports that the enemy has sufficient raw material and the fact of the early interest of enemy scientists in the problem must be explained away before we can safely disregard the possible use of this weapon.5

Groves was being conservative about the intelligence — none of it definitely proved that the Germans weren’t working on a bomb, they just were reporting that they couldn’t see a bomb project. This is a common bind for interpreting foreign intelligence: just because you don’t see something, doesn’t mean it isn’t there (you may have missed it), but on the other hand, proving a negative can be impossible. (This problem, as I am sure the reader appreciates, still exists with regards to alleged WMD programs today.) In Groves’ mind, until there was really zero basis for doubt, they had to proceed as if the Germans were building a bomb.

1944-01-17 - Groves to Dill - R05 T08 F18

But over the course of 1944, there are many accounts which indicate that the Americans at the top of the project, at least, were fearing a German bomb less and less. When Secretary of War Henry Stimson briefed several select Congressmen on the bomb work in February 1944, he had emphasized that “we are probably in a race with the enemy.” By contrast, when he briefed some of the same Congressmen that June, Stimson told them that “in the early part of this effort  we had been in a serious race with Germany, and that we felt that at the beginning they were probably ahead of us.” Note the past tense — at this point, they were using the fears of the German bomb project to justify their earlier efforts, not their current ones. Vannevar Bush, who was at the meeting, emphasized in his notes that he told the Congressmen a bit more about “what we know and do not know about German developments,” but concluded with the thought that since the Allies began the heavy bombing of German industrial sites, the odds were that the Americans were “probably now well ahead of them.”6

Finally, in late November 1944, Samuel Goudsmit, head of the Alsos project, concluded that after inspecting documents, laboratory facilities, interviewing scientists, and doing radiological surveys of river water, that “Germany had no atom bomb and was not likely to have one in a reasonable time.” This was reported back to Groves, who appears to have not been entirely convinced until the total confiscation of German material and personnel was completed in the spring of 1945 and the end of the European phase of World War II. Even Goudsmit was unsure whether the conclusion was justified until they had confirmed it with further investigations.7

By the end of 1944, even the scientists at Los Alamos seem to have realized that Germany was no longer going to be the target. Joseph Rotblat, a Polish physicist in the British delegation to the laboratory, was the only one who left, later saying that “the whole purpose of my being in Los Alamos ceased to be” once it was clear the Allies weren’t really in a “race” with the Nazis.8

Several members of the Alsos mission, with Samuel Goudsmit, the scientific director, at far left. Source: Wikipedia.

Several members of the Alsos mission, with Samuel Goudsmit, the scientific director, at far left. Source: Wikipedia.

So, in a sense, the final confirmation — the absolute confirmation — that the Germany didn’t have an atomic bomb only came when the Germans had totally surrendered. By late 1944, however, it had become clear that their bomb project was, as Goudsmit put it, “small-time stuff.” By mid-1944, the top American civilian official (Stimson) was already minimizing the possibility of German competition. By the end of 1943, British intelligence had concluded the German program was probably not a serious one. We have here a sliding scale of “knowledge,” with gradually increasing confidence, with no clear point, except arguably the “final” one, to say that the Allies “knew” that they were not in a race with the Germans. For someone like Groves, it was convenient to point to the uncertainty of the intelligence assessments, because the possibility of a German bomb, even one very late in the war, was so unacceptable that it could be used to justify nearly anything.

How much does it matter? Well, it does complicate the moral or ethical questions about the bomb project. If you are making an atomic bomb to stop Hitler, well, who could argue with that? But if you are making a bomb to use it against a non-nuclear power, to use it as a military weapon and not a deterrent, then things start to get problematic, as several scientists working on the project emphasized. Even Vannevar Bush, who supported using the bomb on Japan, emphasized this to Roosevelt in 1943, telling the President that “our point of view or our emphasis on the program would shift if we had in mind use against Japan as compared with use against Germany.”9

The degree to which the goals of the atomic bomb program shifted — from building a deterrent to building a first-strike weapon — is something often lost in many historical descriptions of the work. It makes the early enthusiasm and later opposition of some of the scientists (such as Leo Szilard) seem like a change of heart, when in reality it was the goals of the project that had shifted. It is, in part, a narrative about the shifting of perspective from Germany to Japan. Like the Allied knowledge of the German program, it was not an abrupt shift, but a gradual one.

  1. The best source for what the Germans were actually doing is still Mark Walker, German National Socialism and the Quest for Nuclear Power, 1939-1949 (Cambridge: Cambridge University Press, 1989), and Mark Walker, Nazi Science: Myth, Truth, And The German Atomic Bomb (New York: Plenum Press, 1995). []
  2. Of course, this assumes Alsos got everything right, and it is not entirely clear that they did. There are still several interesting historical questions to be answered about the German program. As I’ve written elsewhere, I don’t think Rainer Karlsch’s work on the German atomic program is compelling in its final thesis, but many of the documents he has found do point towards the Alsos mission having some limitations in what it was able to find and recover, and towards further work to be done in fully understanding the German program. []
  3. Arthur Compton to Vannevar Bush (22 June 1944), copy in Bush-Conant File Relating the Development of the Atomic Bomb, 1940-1945, Records of the Office of Scientific Research and Development, RG 227, microfilm publication M1392, National Archives and Records Administration, Washington, D.C., n.d. (ca. 1990), Roll 7, Target 10, Folder 75, “Espionage.” Compton refers to “copper,” which was then the American code-name for plutonium, and “magnesium,” a code-name for enriched uranium. []
  4. The best overall source on US efforts to get information about the German bomb program, and the source of much of this paragraph’s information, Jeffrey Richelson, Spying on the Bomb: American Nuclear Intelligence from Nazi Germany to Iran and North Korea (New York: W.W. Norton, 2006), chapter 1. []
  5. Leslie R. Groves to John Dill (17 January 1944), copy in Correspondence (“Top Secret”) of the Manhattan Engineer District, 1942-1946, microfilm publication M1109 (Washington, D.C.: National Archives and Records Administration, 1980), Roll 5, Target 8, Folder 18, “Radiological Defense.” []
  6. Vannevar Bush to H.H. Bundy (24 February 1944), and memo by Vannevar Bush on meeting with Congressmen (10 June 1944), copies in Correspondence (“Top Secret”) of the Manhattan Engineer District, 1942-1946, microfilm publication M1109 (Washington, D.C.: National Archives and Records Administration, 1980), Roll 2, Target 8, Folder 14, “Budget and Fiscal.” []
  7. Samuel Goudsmit, Alsos (New York: H. Schuman, 1947), on 71; see also Richelson, Spying on the Bomb, chapter 1. []
  8. Joseph Rotblat, “Leaving the bomb project,” Bulletin of the Atomic Scientists (August 1985), 16-19, on 18. See also my post discussing some of the alternative/contributing factors regarding Rotblat’s leaving the project, as discussed by Andrew Brown in his book, The Keeper of the Nuclear Conscience: The Life and Work of Joseph Rotblat (New York: Oxford University Press, 2012). []
  9. Vannevar Bush, “Memorandum of Conference with the President” (June 24, 1943), copy in Bush-Conant File Relating the Development of the Atomic Bomb, 1940-1945, Records of the Office of Scientific Research and Development, RG 227, microfilm publication M1392, National Archives and Records Administration, Washington, D.C., n.d. (ca. 1990), Roll 2, Target 5, Folder 10, “S-1 British Relations Prior to the Interim Committee No. 2.” []

The plot against Leo Szilard

Friday, October 23rd, 2015

One of the recurring themes on WGN America’s Manhattan is the willingness of Manhattan Project security to use extreme extrajudicial methods against scientists on the project they found suspicious, problematic, or dangerous. Episode 2 of this second season centered on an extreme case of this, with the main character, fictional scientist Frank Winter, being locked up without Constitutional protections (to say the least) in an effort to discover where his true loyalties lay. As ought to be pretty obvious, this isn’t (as far as we know) something that happened in real life: you can’t lock up all of your scientists if you expect to get a bomb built before the war ends.

However, this aspect of the plot is inspired by a healthy dose of actual history — even if it is history that is not always well-known. General Leslie Groves and the Manhattan Project security services did occasionally dabble in extrajudicial authority, taking advantage of the fact that the bomb project had its own, wholly autonomous security and intelligence force, and that wartime pressures allowed them to do things that were quite a bit outside of business-as-usual.

An agitated, concerned Leo Szilard in 1960. Source: Emilio Segrè Visual Archives.

An agitated, concerned Leo Szilard in 1960. Source: Emilio Segrè Visual Archives.

Leo Szilard is one of the many historical characters who is distilled into Frank Winter’s personality. Szilard is one of the real characters of the Manhattan Project. A Hungarian émigré, he was the one who came up with the idea of the nuclear chain reaction, he was the one who urged the scientists self-censor their research, he was the one who got his friend Albert Einstein to write a letter to President Roosevelt calling for government coordination of fission research, and he was the one who circulated a petition against the dropping of the atomic bomb during the war. Frank Winter’s moral arc — moving from deep conviction about the need to rapidly build a bomb, to plaguing doubts — is heavily inspired by Szilard.1

But Szilard could also be a huge pain in the neck. He was a natural gadfly, brilliant and utterly lacking respect for authority. It wasn’t just the military he ran into trouble with. The scientists Arthur Compton, Vannevar Bush, and James Conant all eventually ran afoul of Szilard’s views on what they ought to be doing, and each of them in turn found themselves highly irritated with Szilard. If Szilard worked under you, he inevitably became frustrated with you and your decisions, because no one was good enough for Leo Szilard. And his complete inability to just grin and bear it guaranteed that, over time, that feeling of frustration would become mutual. This put even his allies in a tough place, because while no one could deny Szilard’s brilliance or contributions to the bomb project, they also didn’t want to spend too much time with him.

Szilard's folder from the Manhattan Engineer District files.

Szilard’s folder from the Manhattan Engineer District files.

But it was General Groves who really, really took an active dislike to Szilard. His views on him are aptly discussed in a June 1945 memo that Groves had drawn up:

Szilard is a physicist who has worked on the project almost since its inception. He considers himself largely responsible for the initiation of the project, although he really had little to do with it. When the Army took over the project, an intensive investigation was made of Szilard because of his background and uncooperative attitude on security matters. This investigation and all experience in dealing with him has developed that he is untrustworthy and uncooperative, that he will not fulfill his legal obligations, and that he appears to have no loyalty to anything or anyone other than himself. He was retained on the project at a large salary solely for security reasons.2

In the postwar, Groves was even more to the point. Szilard was, he explained to an interviewer, “the kind of man that any employer would have fired as a troublemaker.”3

Szilard and the military were a particularly bad fit. Szilard thought the military did things badly, and, in the end, that there were some bad people at the top. He didn’t hide his feelings on the matter. Rather, he blatantly told many people them — he feared the American military would assert a dictatorship, would use the bombs in a terrible way, and would jeopardize the future peace of the planet.

General Leslie Groves speaking to workers at Hanford in 1944. Source: Emilio Segrè Visual Archives.

General Leslie Groves speaking to workers at Hanford in 1944. Source: Emilio Segrè Visual Archives.

And, from a certain perspective, he wasn’t too far off the mark. The Manhattan Project was asserting quasi-dictatorial powers during the war (and the bomb did bring with it rigid hierarchies, abnormal secrecy, and a lack of democratic process wherever it went in the Cold War), they were planning to use the bomb on civilians to make their point (which one can agree with or disagree with as a strategy), and they were decidedly not interested in any approach to world peace other than building up a large American nuclear arsenal (which in Szilard’s mind was a path to global suicide).

So you can see why he occasionally felt he might be better off not connected with such a project, and why he did (multiple times) attempt to jump the “chain of command” to contact civilian authorities (including both Presidents Roosevelt and Truman) to speak to him about his fears.

And you can understand why General Groves found this sort of behavior tantamount to treason. But as long as Szilard was under the watchful eye of the Manhattan Project security apparatus, Groves would tolerate him for the duration of the war — it was better to have Szilard close (and thus known), than it was to have him “in the wind.”

The draft of Grove's order for the internment of Leo Szilard, 1942.

The draft of Grove’s order for the internment of Leo Szilard, 1942.

But in October 1942, for one brief moment, it was feared that Szilard might quit the project. Compton had attempted to move him out of the project in Chicago, and worried that Szilard might just take off. He was wrong — they worked out an agreement — but the fear of a disgruntled Leo Szilard prompted Groves to draw up a draft of an extraordinary order in the name of the Secretary of War:

October 28, 1942

The Honorable,
The Attorney General.

Dear Mr. Attorney General:

The United States will be forced without delay to dispense with the services of Leo Szilard of Chicago, who is working on one of the most secret War Department projects.

It is considered essential to the prosecution of the war that Mr. Szilard, who is an enemy alien, be interned for the duration of the war.

It is requested that an order of internment be issued against Mr. Szilard and that he be apprehended and turned over to representatives of this department for internment.

Sincerely yours,

Secretary of War.4

It was never sent. As far as we know, Groves never interned anyone in this manner during the war — though he did entertain the idea at least one other time, in the case of Hans Halban, another immigrant nuclear scientist with strong opinions and dubious loyalties (Halban was French, which is Groves’ book ranked slightly worse than Hungarian).

The stalking of Leo Szilard: excerpt from a report by a Special Agent of the Counter Intelligence Corps of Szilard's movements during a 1943 trip to Washington, DC.

The stalking of Leo Szilard: excerpt from a report by a Special Agent of the Counter Intelligence Corps of Szilard’s movements during a 1943 trip to Washington, DC.

But he didn’t leave Szilard alone. He kept a close watch on Szilard and Szilard’s associates, even having the scientist tailed by Special Agents are various times during the war. He never learned very much of interest from these tails (and from the reports of Szilard’s actions, one suspects Szilard was at times aware of them), but one can imagine how delighted he would have been to have a good reason to throw Szilard in a cell and lose the key. “The investigation of Szilard should be continued despite the barrenness of the results,” Groves wrote in June 1943. “One letter or phone call once in three months would be sufficient for the passing of vital information.”5

Groves kept up an active Szilard file through 1946. Szilard knew a lot, and Groves did not trust him. There is evidence in the files that Groves was trying to build an espionage case against Szilard around the time Szilard was trying to circulate his petitions against the dropping of the atomic bomb. But, no doubt to Groves’ frustration, it came to nothing.

But Groves kept Szilard on the payroll. Keep your friends close, and your gadfly scientists even closer, I suppose.

Groves and Szilard — two worthy opponents. Source: Emilio Segrè Visual Archives.

Groves and Szilard — two worthy opponents. Source: Emilio Segrè Visual Archives.

Can we imagine a world in which things had gone another way? In which Groves might have decided that the fear of a free-range Leo Szilard, running around the world doing who-knows-what and talking to who-knows-who, would be worth locking him up without hearing, representation, or appeal? What is one scientist in the light of the stakes that someone like Groves attached to this project?

It is impressive, in retrospect, that Groves, in the end, showed as much restraint as he did — Szilard was a troublemaker. But arguably, some of that trouble needed to be made.

  1. On Szilard’s petitions, Gene Dannen has compiled them all on his Leo Szilard website. []
  2. Leslie Groves, “Resumé of Szilard and Pregel,” (1 June 1945), in Correspondence (“Top Secret”) of the Manhattan Engineer District, 1942-1946, microfilm publication M1109 (Washington, D.C.: National Archives and Records Administration, 1980), Folder 12: “Intelligence and Security,” Roll 2, Target 6. []
  3. Quoted in Richard Rhodes, The Making of the Atomic Bomb (New York: Simon and Schuster, 1986), 502. []
  4. As can be seen from the image, there were several edits made to the draft; I have applied them all in the quotation. Draft letter for the internment of Leo Szilard (28 October 1944), in Manhattan Engineer District records, Records of the Army Corps of Engineers, Record Group 77, National Archives and Records Administration, College Park, Maryland, Box 88, Folder 201, “Szilard, Leo.” []
  5. Leslie R. Groves to Captain Calvert, “Background Information concerning certain Radiation Laboratories and Los Alamos Employees,” (12 June 1943), in Manhattan Engineer District records, Records of the Army Corps of Engineers, Record Group 77, National Archives and Records Administration, College Park, Maryland, Box 88, Folder 201, “Szilard, Leo.” See also, Report of Counter Intelligence Corps Special Agent Charles N. Ronan, “Subject; Dr. Leo Szilard,” (24 June 1943), in the same folder. []

A bomb without Einstein?

Friday, June 27th, 2014

If Albert Einstein had never been born, would it have changed when nuclear weapons were first produced? For whatever reason, I’ve seen this question being asked repeatedly on Internet forums, as odd as it is. It’s kind of a silly question. You can’t go in and tweak one variable in the past and then think you could know what the outcome would be. History is a chaotic system; start removing variables, who knows what would happen. Much less a variable named Albert Einstein, one of the most influential physicists of the 20th century, and whose importance extended well past the equations he wrote… and those were pretty important equations, at that!

1946 - Einstein Time magazine - detail

Einstein’s 1946 cover of Time magazine. The mushroom cloud is a beautifully executed combination of the Trinity and Nagasaki mushroom clouds.

On the other hand, this kind of science-fiction counterfactual can have its usefulness as a thought experiment. It isn’t history, but it can be used to illustrate some important aspects about the early history of the atomic bomb that a lot of people don’t know, and to undo a little bit of the “great man” obsession with bomb history. Albert Einstein has been associated with the bomb both through his famous mass-energy equivalence calculation (E=mc²) and because of the famous Einstein-Szilard letter to Roosevelt in 1939. On the face of it, this gives him quite a primary role, and indeed, he usually shows up pretty quickly at the beginning of most histories of the Manhattan Project. But neither E=mc² nor the Einstein-Szilard letter were as central to the Manhattan Project’s success as people realize — either scientifically or historically.

In terms of the science, E=mc² gets a lion’s share of attention, most perfectly expressed by Einstein’s portrait on the cover of Time magazine in 1946 (above) with his equation emblazoned on a mushroom cloud. A lot of people seem to think that E=mc² played a key role in the development of the bomb, that the weapon just falls out of the physics. This is wrong. The equation can help one understand why atomic bombs work, but it doesn’t really tell you how they work, or whether you would expect them to even be possible.

The way I like to put it is this: E=mc² tells you about as much about an atomic bomb as Newton’s laws do about ballistic missiles. At some very “low level” the physics is crucial to making sense of the technology, but the technology does not just “fall out” of the physics in any straightforward way, and neither of those equations tell you whether the technology is possible. E=mc² tells you that on some very deep level, energy and mass are equivalent, and the amount of energy that mass is equivalent is gigantic. But it says nothing about the mechanism of converting mass into energy, either whether one exists in the first place, or whether it can be scaled up to industrial or military scales. It gives no hints as to even where to look for such energy releases. After the fact, once you know about nuclear fission and can measure mass defects and things like that, it helps you explain very concisely where the tremendous amounts of energy come from, but it gives you no starting indications.

Eddington's famous plate of the 1919 solar eclipse, which helped confirm Einstein's theory of General Relativity. Very cool looking, and interesting science. But not relevant to atomic bombs. Source.

Eddington’s famous plate of the 1919 solar eclipse, which helped confirm Einstein’s theory of General Relativity. Very cool looking, and interesting science. But not relevant to atomic bombs. Source.

What about the rest of Einstein’s main theoretical work, both Special and General Relativity Theory? They are pretty irrelevant to bomb-making. The physical processes that take place inside atomic bombs are what physicists call “non-relativistic.” Relativity theory generally only shows its hand when you are talking about great speeds (e.g. large fractions of the speed of light) or great masses (e.g. gravitational fields), and neither of those come into play with fission bombs. You can neglect relativity when doing the math to make a bomb.1

An intelligent follow-up question might be: “well, just because relativity theory didn’t play a role in the bomb process itself doesn’t answer the question of whether it started physics on a path that led to the bomb, does it?” Without getting into a long timeline of the “science that led to the bomb,” here, I think we could reasonably summarize the situation like this: Einstein’s 1905 papers (of which E=mc² was one) did indeed play a role in the subsequent developments that followed, but perhaps not as direct a one as people think. E=mc² didn’t inspire physicists to start looking into processes that converted mass to energy — they were already looking into those through an entirely separate (and earlier) line of development, namely the science of radioactivity and particle physics. The fact that huge amounts of energy were released through nuclear reactions, for example, had already been studied closely by the Curies, by Ernest Rutherford, and by Frederick Soddy prior (but only just) to 1905.

Arguably, the most important work Einstein did in this respect was his work on the photoelectric effect (for which he was awarded the Nobel Prize in Physics for 1921), which helped establish the physical reality of Max Planck’s idea of a quantum of energy, which helped kick off investigations into quantum theory in earnest. This had a big influence on the later direction of physics, even if Einstein himself was never quite comfortable with the quantum mechanics that developed in subsequent decades.

The Hahn-Meitner-Strassman experiment apparatus, at the Deutsches Museum in Munich. My own photo.

The Hahn-Meitner-Strassman experiment apparatus, at the Deutsches Museum in Munich. My own photo.

Did any of the relativity work lead, though, down the path that eventually arrived at the discovery of fission in 1939? I don’t think so. The experiments that Hahn, Meitner, and Strassman were doing in Berlin that lead to the discovery of fission in uranium were themselves careful replications of work that Fermi had done around 1934. Fermi’s work came directly out of an experimentalist, nuclear physics context where physicists were bombarding substances with all manner of subatomic particles to see what happened. It was most directly influenced by the discovery of the neutron as a new sub-atomic particle by Chadwick in 1932. This came out of work on atomic theory and atomic modeling that was being done by Rutherford and his students from the early 1910s-1920s. And this early nuclear physics came, most directly, out of the aforementioned context of radioactivity and experimental physics of the late 19th century.

None of which has a strong, direct connection to or from Einstein’s work in my mind. They have some overlaps of interest (e.g. Bohr was a student of Rutherford’s), but the communities working on these sorts of experimental problems are not quite the same as the more theoretical circle that Einstein himself worked in.2 If we somehow, magically, removed Einstein’s early work from the equation here, does the output change much? There would be some reshuffling, probably, but I sort of think that Rutherford would still be doing his thing anyway, and from that much of the other work that led to the bomb would eventually come out, even if it had a somewhat different flavor or slightly different timeline.

My least favorite way of depicting the fission process, where energy (E) is a magic lightning bolt coming out of the splitting atom. In reality, most of the energy comes in the form of the two fission products (F.P. here) repelling from each other with great violence. Source.

This is my least-favorite way of depicting the fission process, where energy (E) is a magic lightning bolt coming out of the splitting atom. In reality, most of the energy comes in the form of the two fission products (F.P. here) repelling from each other with great violence. Source.

Do you even need to know that E=mc² to make an atomic bomb? Perhaps surprisingly, you don’t! There are other, more physically intuitive ways to calculate (or measure) the energy release from a fission reaction. If you treat the fission process as being simply based on the electrostatic repulsion of two fission products, you get essentially the same energy output in the form of kinetic energy. This is how the physics of fission is often taught in actual physics classes, because it gives you a more concrete indication of how that energy is getting released (whereas E=mc² with the mass-defect makes it seem like a magical lightning bolt carries it away). There are other more subtle physical questions involved in making a bomb, some of which have Einstein’s influence on them in one way or another (e.g. Bose–Einstein statistics). But I think it is not totally crazy to say that even if you somehow imagine a world in which Einstein had never existed, that the physics of an atomic bomb would still work out fine — Einstein’s specific technical work wasn’t central to the problem at all. We also have not brought up the question of whether without Einstein, relativity in some form would have been discovered anyway. The answer is probably “yes,” as there were people working on similar problems in the same areas of physics, and once people started paying a close attention to the physics of radioactivity they were bound to stumble upon the mass-energy relationship anyway. This isn’t to denigrate or underestimate Einstein’s influence on physics, of course. What makes Einstein “Einstein” is that he, a single person, pulled off a great number of theoretical coups all at once. But if he hadn’t done that, there’s no reason to think that other people wouldn’t have come up with his theoretical insights individually, if slightly later.

A postwar re-creation of the genesis of the Einstein-Szilard letter.

A postwar re-creation of the genesis of the Einstein-Szilard letter.

What about Einstein’s most direct role, the famous Einstein-Szilard letter of 1939 that influenced President Roosevelt to set up the first Uranium Committee? This is a tricky historical question that could have (and may at some point) an entirely separate blog post relating to it. Its writing, contents, and influence are more complex than the standard “he wrote a letter, FDR created the Manhattan Project” understanding of it that gets boiled down in some popular accounts. My feeling about it, ultimately, is this: if the Einstein-Szilard letter hadn’t been written, it isn’t clear that anything would be terribly different in the outcome in terms of making the bomb. Something like the Uranium Committee might have been started up anyway (contrary to popular understanding, the letter was not the first time Roosevelt had been told about the possibility of nuclear fission), and even if it hadn’t, it isn’t clear that the Uranium Committee was necessary to end up with a Manhattan Project. The road from a fission program whose primary output was reports and a fission program whose primary output was atomic bombs was not a direct one. By early 1941, the Uranium Committee had failed to convince scientist-administrators that atomic bombs were worth trying to build. They had concluded that while atomic bombs were theoretically feasible, they were not likely to be built anytime soon. Had things stayed there, it seems unlikely the United States would have built a bomb ready to use by July/August 1945.

The “push” came from an external source: the British program. Their MAUD Committee (an equivalent of the Uranium Committee) had concluded that a nuclear weapon would be much easier to build than the United States had concluded, and sent an emissary (Mark Oliphant) to the United States to make sure this conclusion was understood. They caught Vannevar Bush’s ear in late 1941, and he (along with Ernest Lawrence, Arthur Compton, and others) wrested control of the uranium work out of the hands of the Uranium Committee, accelerated the work, and morphed it into the S-1 Committee. The name change is significant — it is one of the more vivid demonstrations of the increased degree of seriousness with which the work was taken, and the secrecy that came with it. By late 1942, the wheels for the full Manhattan Project were set into motion, and the work had become a real bomb-making program.

Einstein wasn’t involved with any of the later work that actually led to the bomb. He almost was, though: in late 1941, Bush considered consulting Einstein for help on the diffusion problem, but opted not to push for it — both because Einstein wasn’t regarded as politically reliable (he had a fat FBI file), and his approach to physics just wasn’t very right for practical problems.3 Bush decided that Einstein would stay out of the loop.

Usual, rare anti-Nazi propaganda postcard from 1934, showing Hitler expelling Einstein from Germany, titled "The Ignominy of the 20th Century." It is one of the most blatant visual renderings of Einstein as a "scientific saint." Source.

Unusual, rare anti-Nazi propaganda postcard from 1934, showing Hitler expelling Einstein from Germany, titled “The Ignominy of the 20th Century.” It is one of the most blatant visual renderings of Einstein as a “scientific saint.” Source.

Let’s sum it up. Did Einstein play a role in the creation of the atomic bomb? Of course — his physics isn’t irrelevant, and his letter to Roosevelt did start one phase of the work. But both of these things are less prominent than the Time-magazine-cover-understanding makes them out to be. They weren’t central to what became the Manhattan Project, and if you could somehow, magically, remove Einstein from the equation, it isn’t at all clear that the atomic bomb wouldn’t have been built around the time it actually was built. I don’t think you can really credit, or blame, Einstein for the atomic bomb, in any direct fashion. Einstein did play a role in things, but that role wasn’t as crucial, central, or direct as a lot of people imagine. If you could magically drop him out of history, I think very little in terms of atomic bombs would have been affected.

So why does the Einstein and the bomb myth persist? Why does everybody learn about the Einstein letter, if it wasn’t really was sparked the Manhattan Project? There are two answers here, I think. One is that Einstein was, even before the war, one of the best-known, best-recognized physicists of the 20th century, and was synonymous with revolutionary science and genius. Having him “predict” the atomic bomb with equations in 1905 — 40 years before one was set off — is the kind of “genius-story” that people love, even if it obscures more than it enlightens. It also has a high irony quotient, since Einstein was forced to flee from Germany when the Nazis took power.

But there’s another, perhaps more problematic aspect. In many early copies of the Smyth Report that were distributed by the government, copies of the Einstein letter were mimeographed and loosely inserted. The magnification of Einstein’s role was purposefully encouraged by the government in the immediate period after using the weapon. (And it was even a convenient myth for Einstein, as it magnified his own importance and thus potential influence.) Hanging the atomic bomb on Einstein’s head was an act of self-justification, of sorts. Einstein was the world’s greatest genius in the eyes of the public, and he was a well-known pacifist, practically a scientific saint. After all, if Einstein thought building a bomb was necessary, who could argue with him?

  1. As Robert Serber puts it: “Somehow the popular notion took hold long ago that Einstein’s theory of relativity, in particular his famous equation E = mc², plays some essential role in the theory of fission. Albert Einstein had a part in alerting the United States government to the possibility of building an atomic bomb, but his theory of relativity is not required in discussing fission. The theory of fission is what physicists call a non-relativistic theory, meaning that relativistic effects are too small to affect the dynamics of the fission process significantly.” Robert Serber, The Los Alamos Primer: The First Lectures on How to Build an Atomic Bomb (University of California Press, 1992), 7. []
  2. For a good, non-teleological, non-bomb-centric approach to the context of 19th- and 20th-century physics, Helge Kragh’s Quantum Generations: A History of Physics in the Twentieth Century (Princeton University Press, 2002), is excellent. []
  3. Einstein wasn’t entirely a head-in-the-clouds physicist, of course. He worked at the patent office, and as Peter Galison has written about, even his famous thought experiments were often motivated by experience with practical problems of time synchronization. And he did help invent a refrigerator with Leo Szilard. But his work on diffusion physics was too abstract, too focused on first-principle analysis, for use in producing a practical outcome. []

Szilard’s chain reaction: visionary or crank?

Friday, May 16th, 2014

Leo Szilard is one of the most fascinating characters of the nuclear age. He was colorful, principled, clever, and often genuinely ahead of his time. And he always shows up early in the story.

Leo Szilard at the University of Chicago in 1954. Source.

Leo Szilard at the University of Chicago in 1954. Source.

Richard Rhodes starts off his The Making of the Atomic Bomb with Szilard’s famous 1933 epiphany:

In London, where Southampton Row passes Russell Square, across from the British Museum in Bloomsbury, Leo Szilard waited irritably one gray Depression morning for the stoplight to change. A trace of rain had fallen during the night; Tuesday, September 12, 1933, dawned cool, humid and dull. Drizzling rain would begin again in early afternoon. When Szilard told the story later he never mentioned his destination that morning. He may have had none; he often walked to think. In any case another destination intervened. The stoplight changed to green. Szilard stepped off the curb. As he crossed the street time cracked open before him and he saw a way to the future, death into the world and all our woe, the shape of things to come. […]

“As the light changed to green and I crossed the street,” Szilard recalls, “it … suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbs one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction. “I didn’t see at the moment just how one would go about finding such an element, or what experiments would be needed, but the idea never left me. In certain circumstances it might be possible to set up a nuclear chain reaction, liberate energy on an industrial scale, and construct atomic bombs.” Leo Szilard stepped up onto the sidewalk. Behind him the light changed to red.1

It makes for a good read, though there are disputes about the exact timing of this apparent epiphany. But the basic fact seems to remain: Leo Szilard thought up the nuclear chain reaction over five years before fission was discovered. But he wasn’t taken seriously.

But what did he really propose at the time, though, and not just in retrospect? And should he have been taken more seriously? This is what I want to discuss at some length here, because it is a point of common confusion in a lot of writing on nuclear history.

Szilard had a really interesting idea in the fall of 1933. He took out a patent on it in the United Kingdom, which he required to be made secret. Was Szilard’s idea really an atomic bomb? Was it even a nuclear reactor?  The reason to suspect it was not, on the face of it, is that nuclear fission hadn’t been discovered in 1933. That didn’t happen until late 1938, and it wasn’t announced until early 1939. So what, really, was Szilard’s idea? And why did he file a (secret) patent on it? Was Szilard ahead of his time, or just a crank?

Szilard patent GB630726

Szilard’s 1934 patent is easily available these days, and is worth looking at carefully with an eye to what it both says and doesn’t says. The patent in question is GB630,726: “Improvements in or relating to the Transmutation of Chemical Elements.”2 He filed the application first in late June 1934, updated it in early July, and finalized it by April 1935. The UK Patent Office accepted it as valid in late March 1936, but it was “withheld from publication” at Szilard’s request under Section 30 of the Patent and Designs Act. It was eventually published in late September 1949, 15 years after it had been originally applied for.

The basic summary of the patent is straightforward:

This invention has for its object the production of radio active bodies[,] the storage of energy through the production of such bodies, and the liberation of nuclear energy for power production and other purposes through nuclear transmutation.

In accordance with the present invention nuclear transmutation leading to the liberation of neutrons and of energy may be brought about by maintaining a chain reaction in which particles which carry no positive charge and the mass of which is approximately equal to the proton mass or a multiple thereof form the links of the chain.

This sounds awfully promising, especially when you know what you are looking for. It looks like he’s got the right idea, for a reactor at least: it is patent for creating a neutron-based chain reaction. The reason that neutrons matter is because they lack an electrical charge, and so are not repelled by either the protons or the electrons in atoms. This allows them to penetrate into the nucleus. If they can be linked up so that one reaction produces more reaction, they become a chain reaction. Sounds good, especially if we assume that he means an exponential chain reaction (i.e. each reaction produces more than one subsequent reaction).

But once you get beyond the heading, the details of the patent are, frankly, kind of a confused mess.

Szilard doesn’t actually even state that the chain reaction is going to be produced by neutrons. He hedges his bets there — he describes a neutron, essentially, but generalizes the claim for anything that might behave like a neutron. He calls these “efficient particles” (terrible name), and they have to basically be proton-like in mass but lacking a positive charge. OK, fine. The neutron had just been discovered in 1932, so Szilard is probably thinking that there might be other possible particles out there that acted the same way.

The really weird stuff comes in when he tries to explain how this really works. He defines a chain reaction as when “two efficient particles of different mass number alternate a ‘doublet chain.'” Wait, what? He gives an example:

C(12) + n(2) = C(13) + n(1)
Be(9) + n(1) = “Be(8)” + n(2)

Let’s unpack this. C-12 is Carbon-12, C-13 is Carbon-13, Be-9 is Beryllium-9, “Be(8)” is Beryllium-8, put in quotes here because Szilard know it is pretty unstable (it has an extremely short half-life before it alpha decays). The weird parts are the neutrons — n(1) is just a regular neutron. n(2) seems to be a dineutron, a particle which does exist but was only discovered in 2012, and is certainly not something you can count on. (Szilard never says it is a dineutron, but he implies that you might be able separate n(2) into n(1)+n(1) with another reaction, so it seems to be just that.)

Leo Szilard

So the idea here is that the Carbon-12 absorbs a dineutron, emits a neutron, which is then absorbed by the Beryllium-9, which emits another dineutron. It’s essentially a linear chain reaction, which is not nearly as impressive or fast as an exponential chain reaction. But it would generate some significant energy: calculating the mass deficit of these equations shows that together the net energy release would be around 3.3 MeV, about 100X less than a fission reaction, but is some 330,000X more powerful than the combustion of a single molecule of TNT (~10 eV).3 You’d also maybe get some alpha particles (from the Be(8) decay), but it isn’t going to generate a lot of neutrons or dineutrons (they are going to be eaten up by the reaction itself).

Szilard then notes that maybe there are exponential ways to do this. He suggests that maybe some elements will create multiple neutrons when irradiated with neutrons, e.g.

 Be(9) n(1) = “Be(8)” + n(1) + n(1)

This is a much more exciting possibility, because if every reaction creates the possibility of two more reactions, now we are talking about a reaction that can grow really dramatically. The only problem here is that this reaction seems to be endothermic; if you use E=mc2 to calculate the mass deficit, it comes out as -1.67 MeV. Which ought to be a hint that it isn’t going to work.

The final specification of Szilard’s reactor chamber, which is much more simple in operation than it at first appears.

Szilard then continues by saying that he could make this work well if only he knew what elements might behave this wayWhich is really the crux of it, of course. Szilard has no evidence that any element behaves this way. He has no a priori reason to think any of them do. It’s just a pie-in-the-sky idea: what if there were elements that, when they absorbed one neutron, released two? But Szilard doesn’t dwell on this lack of knowledge. He immediately moves on to how he would design a simple reactor if an element was found. It is nothing terribly interesting: he describes a way to create neutrons and aims them at the reacting substance, then siphons off heat with a heat exchanger and uses it to run a turbine.

In July 1934, Szilard filed an “additional specification” — another patent claim attached to his original patent application. It is an elaboration on the reactor idea. Since he still doesn’t know what fuel would make it run, it’s still not very interesting, other than the fact that he’s put a lot of evident work into figuring out some of the basic properties of the reactor despite not having any clue how its core would actually work. Interestingly he does discuss uranium, but not as a fuel (he thinks it would maybe emit X-rays if he shot high energy electrons at it).

Finally, in April 1935 he filed the last, “Complete” specification. This is more or less identical to a combination of the previous two, except he further makes explicit that he thinks there are going to be “explicit particles” other than neutrons that might work. Basically he asserts that there are probably “heavier isotopes of the neutron”4 and that “It is essential that two isotopes of the neutron should take part in the reaction in order to obtain a chain” (my emphasis). The latter instance shows that he is still not thinking of this quite right — it is not essential that there are multiple isotopes of neutrons.

In his examples, he believes that a “tetraneutron” (i.e. n(4)) exists and can play a role in the reactions. (I know nothing of tetraneutrons, but Wikipedia says that they were claimed to be discovered in 2002 but that the experiments could not be replicated.) Szilard seems to be basing his patent claims here on experiments, but it’s not clear whether he did them or someone else did them, but it seems likely he’s misinterpreting the data. It’s a very odd argument, and he rests quite a lot on it — he seems to think it is far more likely that a nuclear reaction will release bunches of bound neutrons (dineutrons, tetraneutrons) instead of multiples of free neutrons (i.e. as fission does). And then the whole thing was kept secret until 1949 — an awful long time for something that actually reveals nothing of any practical utility, much less military applications.

According to The Collected Works of Leo Szilard, there was an additional claim in his patent application of March 1934 that Szilard had removed from the final specification:

(a) Pure neutron chains, in which the links of the chain are formed by neutrons of the mass number 1, alone. Such chains are only possible in the presence of a metastable element. A metastable element is an element the mass of which (packing fraction) is sufficiently high to allow its disintegration into its parts under liberation of energy. Elements like uranium and thorium are examples of such metastable elements; these two elements reveal their metastable nature by emitting alpha particles. Other elements may be metastable without revealing their nature in this way.5

This is much, much closer to the truth, although it is still somewhat unclear what Szilard really thinks about this. It’s not clear whether he’s describing radioactive decay in the traditional sense, nuclear metastability (which is something different altogether), or something different. Uranium and thorium are radioactive and undergo alpha decay — that, by itself, doesn’t actually indicate that they are good candidates for the kinds of reactions Szilard is thinking about. Szilard doesn’t think they are going to split, he thinks they are going to become artificially radioactive. Not the same thing at all. Still, this is a lot closer to the correct formulation, but we have to read it in the context of everything else he put in the patent.

Anyway, so what’s the verdict? Does the patent describe a bomb? Does it even describe a reactor? Definitely not a bomb, and not really a reactor. Most of Szilard’s energies on the patent are describing something that would, at best, take an input amount of energy and magnify it a bit: you’d use a cathode ray to generate high energy electrons, which would generate high energy neutrons, which would stimulate linear chain reactions that would create radioactive byproducts and release a little energy. Maybe you could keep it self-sustaining but it seems like kind of a long-shot to me.6

An animated version of the above "reactor" operating in a pulsed fashion.

A crudely animated version of the 1934 “reactor” operating in a pulsed fashion, just in case you are having trouble visualizing it.

If you read the patent today with the benefit of hindsight, it’s easy to see where Szilard was right and where he was wrong. There is a germ of rightness in the patent, but it is clouded by a fog of wrongness, or at least confusion. I’m not blaming Szilard for this, of course. Like almost everyone else, he didn’t predict fission. He was ahead of his time, in the sense of anticipating that neutrons in particular were going to be important particles for creating nuclear chain reactions. But he didn’t really understand how it would work. As a result, most of the patent involves describing a device that wouldn’t work. To guess even something right about the future is a large task, even if one gets a few things wrong.

So was Szilard a visionary or a crank? To someone in 1934 or 1935, it would have been completely reasonable to dismiss Szilard’s patent as being too speculative and potentially too wrong (dineutrons, tetraneutrons, etc.) to be worth spending time worrying about. It also isn’t clear it has any real military implications — it isn’t even clear it would work as a power source, much less a weapon. To dismiss Szilard as something of a crank prior to the discovery of fission wouldn’t have been wrong. Szilard’s point of reference here isn’t fission, it’s artificial (induced) radioactivity, which had been discovered by the Joliot-Curies just prior to Szilard’s patent filing. But you can’t make artificial radioactivity work the way Szilard wants it to. I don’t fault anyone for not taking him very seriously at the time — because Szilard’s scheme was missing an absolutely essential component, and in its place there were a lot of incorrect assumptions.

After the discovery of fission in late 1938/early 1939, suddenly it is easy to pick out the visionary aspects of Szilard’s work. It suddenly becomes clear that Szilard was, in fact, a little ahead of the game. That if instead of his plans for beryllium-carbon reactions with neutrons and dineutrons, that a simple, neutron-based, exponential chain reaction would be possible with nuclear fission, and that furthermore it would release a lot more energy a lot quicker than what Szilard had dreamed up in the early 1930s.

Which is a conclusion that complicates the simple visionary/crank dichotomy. Szilard wasn’t really either in my mind. He had a germ of a good idea, but not the whole picture. But when the missing element came along, he was uniquely ready to see how it would complete his original idea. That’s the real story here, the real accomplishment: Szilard didn’t have to play catch-up when fission was announced, because he’d already thought a lot of this through. But that shouldn’t lead us to over-estimate the importance of the original patent work — it wasn’t a bomb, it wasn’t really even a reactor. But it did become a useful framework for thinking about fission, when fission came along.

  1. Richard Rhodes, The Making of the Atomic Bomb (Simon and Schuster, 1986), 13 and 28. []
  2. It should not be confused with another patent he filed for at the same time with an identical name (GB440,023) which has nothing to do with chain reactions at all.  GB440,023 is basically a patent for producing artificially radioactive elements. The device it describes involves using a cathode tube to generate X-rays, then using the X-rays to stimulate neutron emission in beryllium, and using those neutrons to make artificially radioactive elements through induced radioactivity. It’s not a bad idea — it is now known as the Szilard-Chalmers method and it works. But it’s not a chain reaction at all . Szilard filed a patent for the same idea in the US as well. That Szilard considered it something quite different is also evidenced by the fact that he doesn’t seem to have tried to keep it secret. He references the basic method in GB630,726 as the driver of the reactions in question. []
  3. The beryllium reaction is endothermic but the carbon one is not. []
  4. “I have reason to believe that apart from neutrons which carry no charge and have a mass approximately equal to the proton mass heavier isotopes of the neutron exist which particles carry no charge and has a mass number approximately equal to a multiple of the proton mass.” []
  5. Quoted in Julius Tabin, Introduction, Part V: Patents, Patent Applications, and Disclosures (1923-1959), The Collected Works of Leo Szilard: Scientific Papers (MIT Press, 1972), on 529. []
  6. The neutron multiplication factor, to use modern reactor terminology, seems to me like it is going to be 1 at best, and probably less than that given inefficiencies, losses, etc. One question unasked and unanswered in the patent is how many neutrons he thinks he is going to produce per blast. I think it is easy to overestimate how effective this would be from that point of view. The neutron initiator used in the Fat Man bomb, as an aside, produced only around 100 neutrons on average. This isn’t the same process at all, but in terms of orders of magnitude this is probably not inaccurate when it comes to imagining how many neutrons can be easily stimulated. It is nothing like what a fission chain reaction can generate with its exponential growth. []

Leo Szilard, war criminal?

Friday, February 14th, 2014

Could Leo Szilard have been tried as a war criminal? Now, before anyone starts to wonder if this is a misleading or inflammatory headline, let me say up front: this was a question that Szilard himself posed in a 1949 story published in the University of Chicago Law Review titled, “My Trial as a War Criminal.” It is a work of fiction, but Szilard was serious about the questions it raised about the morality of the atomic bomb.1

Szilard testifying before Congress in the postwar. From the Emilio Segrè Visual Archives.

Szilard testifying before Congress in the postwar. From the Emilio Segrè Visual Archives.

Leo Szilard is one of the most colorful characters in the story of how the atomic bomb got made. An eccentric Hungarian, one of the “Martians” who emigrated to the United States during World War II, Szilard aspired to always being one step of head of the times. You didn’t have to be much ahead to make a difference, he argued, just a little bit. One example of this he gave in a later interview regards his decision to flee Germany shortly after the Reichstag fire. On the day he left, it was an easy trip on an empty train. The next day, the Germans cracked down on those trying to flee. “This just goes to show that if you want to succeed in this world you don’t have to be much cleverer than other people, you just have to be one day earlier than most people. This is all that it takes.”2 In 1939, Szilard was the one who famously got Albert Einstein to write to President Roosevelt, launching the first US government coordination and funding of fission research. During the Manhattan Project itself, Szilard worked at the University of Chicago, helping to develop the first nuclear reactor (CP-1) with Enrico Fermi. After this, though, his active role in the bomb project declined, because General Groves hated the man and worked to exclude him. He attempted in various ways to influence high-level policy regarding the bomb, but was always shut out.

But after the war, Szilard found his place — as a gadfly. He wasn’t a great bomb developer. He was, however, a great spokesman for the dangers of the atomic bomb. Irrepressible, clever, and impossible-to-look-away-from, Szilard could steal the stage, even if no American could pronounce his name. It is in this context that his article, “My Trial as a War Criminal,” was written. The notes on the University of Chicago Law Review version note that it was written in June 1948, but because of “political tensions” Szilard put it off. With the “relaxation” of tensions, Szilard deemed it possible to publish in the Autumn 1949 issue. One wonders exactly what Szilard had in mind; in any case, given that the US first detected the Soviet atomic bomb in September 1949, and from there launched into the acrimonious debate over the hydrogen bomb, it seems like Szilard’s sense of timing in this instance was either perfect or terrible.

Szilard - My Trial as a War Criminal

My Trial as a War Criminal” starts right after World War III has been fought. The Soviet Union has won, after using a new form of biological warfare against the United States.

I was just about to lock the door of my hotel room and go to bed when there was a knock on the door and there stood a Russian officer and a young Russian civilian. I had expected something of this sort ever since the President signed the terms of unconditional surrender and the Russians landed a token occupation force in New York. The officer handed me something that looked like a warrant and said that I was under arrest as a war criminal on the basis of my activities during the Second World War in connection with the atomic bomb. There was a car waiting outside and they told me that they were going to take me to the Brookhaven National Laboratory on Long Island. Apparently, they were rounding up all the scientists who had ever worked in the field of atomic energy. 

In the story, Szilard was given a choice: he could stand trial for being a war criminal, or he could go to Russia and work with them over there. Szilard opted for the former, claiming he had no capability to learn Russian at that point in his life, and that he had no interest in making himself a servant of Soviet science. He is then interrogated at length about his political views and his work on atomic energy. The Soviets have read his articles in the Bulletin of the Atomic Scientists (“Calling for a Crusade” and “Letter to Stalin“) but think they are naive. Szilard reports no real acrimony, however.

His trial for war crimes begins a month later in Lake Success, New York. He was, “apparently as a special favor,” one of the first to be tried. Two major charges were levied against him. The first was that he had tried to push the United States towards developing nuclear weapons in 1939 (the Einstein-Szilard letter). In the eyes of the prosecutor, this was when World War II was still “an imperialist war, since Germany had not attacked Russia until 1941.” The second charge was that he contributed “to the war crime of dropping an atomic bomb on Hiroshima.”

Szilard has several defensive arguments in his favor. First, he points out that he in fact presented a memorandum to (future) Secretary of State James Byrnes in May 1945 which argued that the atomic bomb should not be first used against Japan cities. This memo had been published in the Bulletin as well in December 1947. Second, he also noted that he circulated a petition in July 1945 that called for not using the bomb as a military weapon before giving the Japanese a chance to surrender first, and that he attempted to put it in front of President Truman himself.

Leo Szilard at the University of Chicago in 1954. Source.

Leo Szilard at the University of Chicago in 1954. Source.

Both of these defenses, however, were easily countered. In the case of the memo to Byrnes, an original copy could not be found, and the Bulletin copy had many deletions for security reasons, any one of which could have contradicted the published material. In the case of the petition to Truman, it was noted that it never made it to Truman, because Szilard submitted it by way of General Groves, who of course squashed it. The Russian prosecutor said that Szilard should have known that the architect of the Manhattan Project would never have transmitted such a thing up the chain of command. So neither were considered adequate at exculpating Szilard.

Szilard is then released on bail. The rest of the story concerns the trials of Secretary of War Stimson, Secretary of State Byrnes, and President Truman. This part revolves around a legal discussion of what it means to be a “war crime.” In the story, the tribunal adopts the definition used at Nuremberg that a war crime was any “violations of the customs of war” and “planning a war in violation of international agreements.” The use of the atomic bombs was necessarily a violation of the customs of war, because it was not customary to drop atomic bombs on other nations during World War II. And the Russian prosecutor was able to gather ample evidence that various US officials had urged war with the Soviet Union under conditions not allowed by the United Nations charter, which only allows war in the face of armed attack. So when Byrnes wrote in a book that the United States should consider “measures of last resort” if the Soviets refuse to leave East Germany, this was taken as evidence of the latter charge. (Refusing the leave occupied territory is not an “armed attack,” and “measures of last resort” can only be understood as implying war.)

Stimson’s section gets the closest to the meat of the question — whether the atomic bombs were justified. Stimson’s defense is the same as his 1947 article from Harper’s — that the bombs were used to hasten the war and to save a net number of lives. The Russians point out, however, that even the US Strategic Bombing Survey concluded that the atomic bombs were not necessary to end the war,3 and that Stimson had access to sufficient intelligence about Japanese communications to know that Japan was on its last legs.

Szilard receives notice — in his bathrobe — that he has won the "Atoms for Peace" award in 1960. Source.

Szilard receives notice that he has won the “Atoms for Peace” award in 1960. At the time, he was in a hospital, being treated (successful) for bladder cancer. Source.

In the end, Szilard notes that practically all of them were expected to be found guilty. But a deus ex machina saves the day — the Soviets’ viral biological agents somehow get out to their own populations, their vaccines fail, and the United States is desperately appealed to for assistance. Under new settlement terms, all war crime prosecutions were ended, and “all of us who had been on trial for our lives were greatly relieved.”

Such ends Szilard’s story. It’s a curious one, and doesn’t go where you might think based on the title alone. Szilard seems to be making a strong point about the way in which war crime tribunals always favor the winners, and that if you apply the Nuremberg standards to the United States’ conduct during World War II and the early postwar, it is clear that no one, even a dissident like Szilard, would be safe. It isn’t a hand-wringing, self-flagellating confession. There is none of the “physicists have known sin” moralizing of J. Robert Oppenheimer. It isn’t even a discussion of what happened regarding the atomic bombing, whether it was justified or not, whether it was terrible or not. It is a gentle story, albeit one that subtly introduces a revisionist argument about the bombings of Hiroshima and Nagasaki, one that continues to be debated to this day.

One can also read the piece as being instead a complaint about the definition of “war crimes” from Nuremberg — are they nothing more than using new weapons and talking about war? The actual Nuremberg principles, also include “wanton destruction of cities, towns, or villages, or devastation not justified by military necessity.” Now whether the atomic bombings fall under that is a tricky question — how does one define “justified by military necessity”? On this sort of unclear requirement, the whole edifice hinges.4

Szilard glasses 1960 LIFE

This whole story came to my attention because Bill Lanouette, author of the Szilard biography Genius in the Shadowse-mailed me after seeing my post on Andrei Sakharov. He noted that according to Rhodes’ Dark Sun, Sakharov was very affected by Szilard’s story. Sakharov showed it to his colleague Victor Adamsky, who reported that:

A number of us discussed it. It was about a war between the USSR and the USA, a very devastating one, which brought victory to the USSR. Szilard and a number of other physicists are put under arrest and then face the court as war criminals for having created weapons of mass destruction. Neither they nor their lawyers could make up a cogent proof of their innocence. We were amazed by this paradox. You can’t get away from the fact that we were developing weapons of mass destruction. We thought it was necessary. Such was our inner conviction. But still the moral aspect of it would not let Andrei Dmitrievich and some of us live in peace.5

What’s interesting to me is that the Soviet weapon designers seem to have read Szilard’s story in a much more moralistic light than I did. For me, Szilard’s story is more about the difficulty of having anything like a consistent stand on what “war crimes” might be — that the actions of the United States could easily be seen from another nation’s perspective as highly damning, even if from a more sympathetic position they might be justifiable. Sakharov and Adamsky apparently understood the story to be about the indefensibility of working on weapons of mass destruction full-stop. It is a curious divergence. Assuming my reading is not naive, I might suggest that the Soviet scientists saw not so much what they wanted to see, but what confirmed their existing, latent fears — something in Szilard’s story resonated with something that they already had inside of them, waiting to be released.

  1. Leo Szilard, “My Trial as a War Criminal,” University of Chicago Law Review 17, no. 1 (Autumn 1949), 79-86. It was later reprinted in Szilard’s book of short stories, The Voice of Dolphins. []
  2. Spencer Weart and Gertrude Weiss Szilard, eds., Leo Szilard: His version of the facts; Selected recollections and correspondence (Cambridge, Mass.: MIT Press, 1978), 14. []
  3. “Based on a detailed investigation of all the facts, and supported by the testimony of the surviving Japanese leaders involved, it is the Survey’s opinion that certainly prior to 31 December 1945, and in all probability prior to 1 November 1945, Japan would have surrendered even if the atomic bombs had not been dropped, even if Russia had not entered the war, and even if no invasion had been planned or contemplated.” []
  4. Szilard’s story also notes that just because these principles were developed after the war ended did not prohibit them from being applied to activities during the war — otherwise all of the Germans would have gotten off the hook. []
  5. Richard Rhodes, Dark sun: The making of the hydrogen bomb (Simon & Schuster, 1995), 582. []