Posts Tagged ‘Vannevar Bush’


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?

  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. []

Biological Warfare: Vannevar Bush’s “Entering Wedge” (1944)

Wednesday, July 25th, 2012

At the end of 1944, Vannevar Bush and James Conant, the atomic administrators at the Office of Scientific Research and Development and the National Defense Research Committee, were starting to worry about what to do about the bomb. Not in the near term — but what to do about it after World War II.

How do you regulate a totally new technology — both domestically and internationally? Where do you begin, in thinking about it? Especially when the technology in question is the atomic bomb, a weapon that seemed to pose insuperable existential questions and seemed capable of revolutionizing not only war, but the idea of nation-states themselves?

General Leslie Groves, James B. Conant, and Vannevar Bush, in August 1945

Bush and Conant, for their part, spent a lot of time looking for analogies: using their experience with other regulatory regimes to inform their understanding of an atomic regulatory regime.

This wasn't their first technological rodeo: Bush had been deeply involved in radio technology regulation in the 1920s, and Conant was a veteran hand when it came both to chemical warfare and, as it happened, the regulation of rubber. (One of the many control approaches they pursued was that of patents, which I've written about pretty extensively.)

But even more pertinently, they worked openly on the problem of regulating biological warfare, with the secret goal of using this as a trial balloon for the types of regulations they'd recommend for the atomic bomb.

The weekly document is a letter from Vannevar Bush to James B. Conant, dated October 24, 1944, on the problem of the long-term control of biological warfare— not just because Bush thought it was important, but because he thought it would help make sense of what to do with the bomb.1

Click image for the PDF.

Bush started it off by referencing a "recent memorandum" to the Secretary of War Henry L. Stimson, which they had sent at the end of September. In that memo, Bush and Conant warned that secrecy wouldn't be a long-term international solution for the bomb, and strongly recommended that Stimson start seriously making moves towards some means of international control of the bomb. Stimson wasn't yet sure, though (he would later become convinced).

He then continued:

I have been giving some thought to another subject recently, and possibly it offers a means of approaching this one [the bomb]. Everyone is now agreed, I think, that biological warfare is not likely to break out in the European Theatre. In the Far East the situation may be more dangerous, especially if chemical warfare is started, but even there I believe that any large-scale biological warfare is highly unlikely for the present war. In fact, excitement on the matter in this country has died down. ...

In the world of the future there may be some danger that biological warfare would be developed in secret by a future aggressor and suddenly sprung upon the world. This depends, I suppose, upon how biological matters develop, but the possibility is already there in some forms.

Bush considers biological warfare to be somewhat of a dead, but scary, letter.  Since it was looking like it would be irrelevant to the current conflict (Bush either didn't know or didn't consider the BW use by Japan again the Chinese to fall under this assessment), it could be talked about relatively openly. Thus they could explore some of the salient questions about the atomic bomb before the bomb itself was outside of secrecy. Pretty clever, Dr. Bush.

The exact plan Bush was shooting around was as follows:

Now it seems to me that this would be far less dangerous if there were full interchange between biological scientists all over the world, especially if this occurred through an international organization, with frequent international conferences on epidemiology held in all of the large countries in turn, and with a central organization collecting public health information, with particular emphasis on the prevention of epidemics. Under such circumstances if one country were developing the military aspects of the matter on a large scale in secret there would be a fair chance, I believe, that it would become known.

Certainly any county that did not have ideas of aggression somewhere in the back of its mind would be inclined to join such an affair genuinely and open up the interchange, unless indeed there is more duplicity in the world than I am inclined to think. It may be well worth while to attempt to bring this about.

The plan, then, was to have complete scientific interchange as a regulatory mechanism. If the work being done is talked about openly, then there would be no "secret arms race."

This is an idea that was quite popular in many circles at the time regarding the bomb, as well. Niels Bohr in particular argued very strongly for this form of "international control": if you got rid of secrecy, he argued, you'd be able to see what everyone was doing, and if all the relevant scientists dropped of the face of the Earth all of the sudden, you'd know they were developing WMDs.2

It's an optimistic idea, one which puts a little too much stock, I think, in the communicative power of scientific exchange. An invitation to a conference is not a verification mechanism. It doesn't take into account the ability of states to stage entirely shadow programs, or to have scientists who are happy to be duplicitious to other scientists. It somewhat naively subscribes to the idea of a transnational scientific community that is "above" politics. Even by World War II such a notion should have been seen as somewhat old fashioned; certainly the Cold War showed it to be.

Still, the goals were laudable, and as a way for thinking through international scientific control, it wasn't the worst approach. Bush and Conant's greatest fear with respects to the bomb was a "secret arms race." They really thought this could not end with anything but mass destruction for all. At least a non-secret arms race, they argued, would keep people from doing anything too stupid.

Bush closes the letter with this wonderful paragraph:

You will readily see that I have in mind more than meets the eye, and am thinking of an entering wedge. However, I would very much like to explore with you this particular thing on its own merits, and also from the standpoint of what its relationship might be to other matters.

Bush was interested in the control of biological warfare, but he was more interested in thinking about the bomb. Biological warfare would be his "entering wedge" in approaching the issue of scientific control, knowing that soon enough they'd be worrying about something he considered even bigger.

  1. Citation: Vannevar Bush to James B. Conant (24 October 1944), 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)." []
  2. The full, more formal plan can be found in Vannevar Bush and James B. Conant, "Memorandum on the Future of Biological Warfare as an International Problem in the Postwar World," (27 October 1944), 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 6, Folder 77, "Interim Committee — International Control." []

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.

  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! []

James Conant’s Atomic Bomb Sketch? (1943)

Friday, May 25th, 2012

I had fun with the little visual mystery I posted last Friday, so here's another one I've been chewing over for awhile.

Drawings of "official" atomic bomb designs are rare. (Where "official" means "created by people who actually build bombs.") It's the sort of thing which is generally kept close — what are released are generally extremely sanitized abstractions, which are then elaborated upon by people without security clearances (like John Coster-Mullen).

So I was somewhat surprised to find, buried in some files of the Office of Scientific Research and Development, this drawing which appears to have been made by none other than James B. Conant, then the President of Harvard University:

That looks an awful lot like the drawing of a gun-type nuclear weapon. But is it?

Conant, of course, was a major scientific administrator during the war. He was a chemist by training, and was no stranger to secret projects: during World War I, he had worked to develop lewisite for use in Europe while working at the "Mousetrap" facility in Cleveland, so called because once you went in, you were never supposed to come out.1 The chemical munitions that Conant worked on were never used in the war; the armistice came just before they were to be shipped out. During World War II, Conant was pals and colleagues with Vannevar Bush, head of the OSRD, and the two of them did quite a lot of work on early atomic development policy.

The context of the sketch is apparently a note from Conant to Bush, dated January 21, 1943 (with notes that it was amended March 10, 1943).  I say "apparently" because, while this follows the other sequentially in the file, it isn't clear that they are attached or from the same period. (The handwriting is Conant's though, which is something. Don't read too much into the fact that the pages look different; one is just scanned in black and white, the other as grayscale.)2

The note itself is pretty hard to decode; it is in Conant's nearly-impossible handwriting. The basic gist of it is that he is estimating how much enriched uranium they can product at Oak Ridge and what that implies about when a bomb would be ready (he seems to think one would ready by September 1944, and then later updates the note to push it back a bit).3

On the "drawing" page itself, there is a list (anything in italics is written by me, trying to make sense of his handwriting):

(1) Metallurgy
(2) cows [!?! see below]
(3) Development of technique for handling material in bulk
.                                          70-80, 90% of critical
(4) What cases are effective? [could this mean casings?]
(5) Further [???] [???] for cross section
(6) No. of neutrons for 49
(7) Capture + emission[?]  of neutr.                          (Bohr)
(8) Cross section of scattering[?]
(9) Firing problem
.                              length of time first mass stays in
(10) Source of neutrons Neutron source
(11) Effect of dilution
(12) Protection against thermal neutrons                (25)

To my eye, even with the ambiguity caused by his bad handwriting, it looks like a list of problems to tackle when thinking about designing a bomb the first time. What will the metallurgy of U-235 or plutonium be like? How will you shape these materials safely on a lathe? Was sorts of casings or reflectors will be best? How do you handle this stuff without getting totally irradiated? How many neutrons will plutonium emit per fission? How will you make a neutron initiator? What's the engineering of the actual bomb assembly going to look like? And so on.

Except, of course, for "cows," which I find inexplicable. It's not a codename I'm familiar with. I am almost surely transcribing it wrong, but it looks a lot like "cows":

Cows. Hmm. There were some cows involved in the Manhattan Project in a peripheral way, but I doubt he was thinking about that at this point. More likely is I'm making a garble of his handwriting again, but now that I've seen "cows," I can't stop seeing it. (Got a better guess? Let me know.)

Anyway, what it looks like to me is the result of either brainstorming or notes from a meeting that Conant was having, all of which seems to pertain to weapon design issues. So the idea that he might have sketched a crude gun-type design at the bottom of it isn't fanciful in and of itself.

The drawing seems to show one "40 lb" piece of fissile material at the bottom of a gun barrel, with the cross section of a ring of the same stuff at the other end of it inside some sort of heavy neutron reflector or tamper. There are some other numbers nearby; it seems to say "10 meters, 30 ft." Is that meant to be the length of the gun barrel? It would be pretty long, much longer than any of the actual bombs estimated for combat, but it might just be a back-of-the-envelope guess.

The bomb — if it is a bomb — that Conant has sketched out here doesn't look much like Little Boy actually looked, but it doesn't look wildly different than Thin Man, the plutonium gun-type bomb that was pursued before Little Boy.

Experimental bomb casings from the aborted "Thin Man" plutonium gun design. There are early "Fat Man" casings designs in the background.

The actual Little Boy weapon used (according to John Coster-Mullen) a cylindrical projectile that weighed around 85 lbs, and the "spike" that it was shot into (not the other way around) weighed 56 lbs, bringing it to a total of 141 lbs of fissile material, considerably more than is shown in this sketch. But still, the entire point of the list seems to be that they don't know the details at that point.

The other possibility is that this isn't a bomb at all, and that it is some kind of "tickling the dragon's tail" criticality experiment. But that's a much more boring conclusion.

Instead of pointing out how crude and inaccurate the drawing is, though, I'm still just amazed that it was hiding on that microfilm, waiting to be stumbled upon. It's oh so rare to see bomb designs in "the wild," and this one is considerably more "real" (in the sense of it being less conceptual and more of an engineering-style layout) that the only other declassified drawings from the same period I have seen (those in the Los Alamos Primer).

Did Harvard's President sketch an atomic bomb on his notepad? I don't know, but it's a very real possibility, is it not? I wonder if any Harvard president since then — much less Harvard's current President — has ever done such a thing.

  1. See James Hershberg’s James B. Conant: Harvard to Hiroshima and the Making of the Nuclear Age (New York: Knopf, 1993), chapter 3. []
  2. Citation: James B. Conant to Vannevar Bush (21 January 1943, amended 10 March 1943), 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 4, Target 3, Folder 21, "Miscellaneous Bush-Conant Material, May 1941-October 1944." []
  3. Here's an attempt by me to decode Conant's handwriting. Anything I've put in italic means "I can't read this."

    Memo to V. Bush               Amended by JBC before [???] on March 10, 1945
    From J.B. Conant              Date Jan. 21, 1943

    The latest news from the electromagnetic front via Gen. Groves is (1) Tennessee Eastman are quite confident that process can be made to work. It now seems quite certain that each tank will yield from 50-300 mg per day.
    At  500 tanks that means 50-150 g per day.
    If priorities can be settled there is a chance this output can begin November 1, 1943 (First set Y tanks Aug 1). [Inserted note:  I ??? this now, March 10, 1943; a bomb will require 24 ???; 100 g a day begins ???, 1944. Will take till ??? 1, 1944 for amount! There is still a chance for a military effort in 44.]  This would yield first first [sic??] bomb Feb 1, 1944, at rate of 100 gm per day. This might mean first mean first military result July 1, 1944 allowing four months for developing bomb and manufacturing material for a second. I still believe barring miracles, best day is Sept 1, 1944 . The Chicago method might come along at the same point. So we have two chances of making that schedule. J.B.C.

    That's not the world's best transcription attempt (I loathe Conant's handwriting, I should probably say), but you can get the gist of it, I think. "The Chicago method" refers to plutonium production. "Y" tanks refer to the electromagnetic method used at Y-12 in Oak Ridge. I'm open to any guesses as to better transcription attempts. Conant's estimate for when they'd have a bomb ready was off by about six months, something I'm sure my German friends are undoubtedly thankful... []


Conant on the Role of the British in the Manhattan Project

Wednesday, March 21st, 2012

The Manhattan Project was a joint effort to build the atomic bomb between the United States, the United Kingdom, and Canada. In practice, most of the labor, expense, and manpower came from the United States, and the degree to which the UK and Canada should be equal partners with the US in the bomb project was a controversial subject.

The British were instrumental in prodding the US into serious action with the MAUD report, and the Canadians had uranium. But should that be it? This was the question in late 1942, when the US program was undergoing a massive transformation. Prior to 1942, the American effort was primarily a research program, trying to answer the question of whether atomic bombs could be built in a reasonable amount of time. From late 1942 onward, the effort shifted to a production program, an all-out effort to try and produce an actual bomb for use in the war. Would the British be let in on this later phase? Did the United States need the British?

Not really, thought James B. Conant, President of Harvard, chairman of the National Defense Research Committee1, and close friend of Vannevar Bush (director of the Office of Scientific Research and Development, which was the civilian side of the Manhattan Project). This week's document is a letter from Conant to Bush from December 1942, outlining the many reasons he thought that the US should essentially abandon the British at that point in the work:2

Click image to view full PDF.

Conant implored Bush to clarify the matter of UK participation before the full-scale bomb project, run by the U.S. Army Corps of Engineers, got under way, "for it will be clearly difficult to continue to have complete scientific interchange on the one hand and restricted development interchange on the other unless the arrangement is carefully spelled out, for the line between research and development is nebulous, and the same people are often involved in both."

For Conant, the decision had to be completely pragmatically. The was "presumably one one reason" to share secret military information between Allied nations, "namely, to further the prosecution of the war in which both are engaged." The question was, would sharing all information with the British do this? He thought not. The British were not producing fissile material, for example, so "our passing our knowledge to them [in that subject] will not assist the British in any way in the present war effort." So under this scheme, the British would only get to participate in the parts that they themselves were working on which would actually get them closer to making an atomic bomb during World War II. Which is to say, bomb design, reactors, and plutonium would be left out of the story for the British. ("If there be any national rights in this whole area '49' [code for plutonium] may be said to be a strictly U.S. invention.")

Would there be complications? Conant acknowledged that if they cut the UK out at this point, Canada might deny them heavy water. That would be annoying, but not a deal-breaker. They might also deny them uranium ore, which would be a somewhat more dicey procedure until the US was sure of its access to domestic supplies. (They had a considerable amount of high-value ore from the Belgian Congo, but this was insufficient for the entire project.) The British, of course, would "certainly be displeased," but Conant concludes that "there would be no unfairness to the British in this procedure."

What would be the advantage to the US in doing this? Conant says simply that it would help with secrecy:

The advantages of restricting all further information to the United States is obvious. Secrecy could be more easily controlled. We are not just reaching the point where the advances are military secrets of the first order of importance.

Conant and Bush were also worried that the British interest in participating in the bomb project had nothing to do with the current war, but with an eye towards scientific and commercial prestige in the postwar period. Conant does not mention this here, though.

There would be many more salvos on this front as Conant and Bush frantically tried to persuade Roosevelt not to let the British into the full, new Manhattan Project. At one point, Bush thought he had convinced FDR of the soundness of this measure.

But however persuasive Vannevar Bush could be, he couldn't match up to Winston Churchill. By mid-1943, Churchill had convinced Roosevelt that full cooperation was the only true path, and the Quebec Agreement was (secretly) entered into. Not only would the British get access to American research, and send a delegation of scientists to Los Alamos, but they would get to have equal say on whether the bombs themselves were used, and whether the US could share the information with any other countries. In practice, though, the British were nearly completely kept out of Hanford (James Chadwick visited it once), though they learned much about plutonium through their work at Los Alamos. The Canadians founded labs at Montreal and Chalk River, but were more or less excluded from American information by General Groves.

Conant would eventually embrace the Quebec Agreement as well. But his initial reason for wanting to keep the British out -- because of the difficulty of controlling secrecy -- proved exactly correct. It was, after all, Klaus Fuchs, a member of the British delegation to Los Alamos, who proved to be the most significant of the wartime atomic spies. Of course, he was wrong the British had nothing to contribute: the British delegation (including Fuchs) made major contributions towards the practical realization of the bomb while at Los Alamos. So maybe it all evens out.

  1. Note that at this point, Office of Scientific Research and Development had taken over most of the responsibilities of the original NDRC. The NDRC became the "NDRC of the OSRD" at this point, which meant that it was merely an advisory body of the OSRD. []
  2. Citation: James B. Conant to Vannevar Bush, "US-British Relations on S-1 Project" (14 December 1942), 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 4, Folder 9, "S-1 British Relations Prior to Interim Committee, [Fldr.] No. 1 [1942]." []