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James B. Conant on Trinity (1945)

by Alex Wellerstein, published July 16th, 2012

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

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

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

The original document isn’t easy to come by — it was withdrawn from the Bush-Conant File when it was microfilmed — but James Hershberg, when writing his great Conant biography (James B. Conant: Harvard to Hiroshima and the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

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

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

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

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


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


125 miles south east of Alburquerque

5:30 a.m. Monday, July 16

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

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

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

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

Trinity fireball drawing by James Conant

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

Conant's drawing of the rising and dissipating mushroom cloud

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

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

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

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

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

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

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

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

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6 Responses to “James B. Conant on Trinity (1945)”

  1. Stan Norris says:

    Alex,
    There have been many estimates for the yields over the years. I like to use a Los Alamos report (LA-8819) by John Malik, The Yields of the Hiroshima and Nagasaki Nuclear Explosions (issued September 1985). It is available on the Web. Though Trinity is not included Malik concludes that the current best estimate for Hiroshima is 15 kt and for Nagasaki 21 kt with 20 percent uncertainity for Hiroshima and 10 percent for Nagasaki. For Trinity then I guess 21 kt would be logical within a range of 19-23 kt.

    • Stan: What are a few kilotons here and there, between friends? ;-) Thanks — the Malik report is pretty interesting, especially in the light of the fact that they were still arguing about that 40 years after the fact!

      I figure a guess of 18 kt for 1945 is pretty good, though, so I’m happy to still give Rabi the pool (certainly a better one than all of the other “heavies,” even if Rabi didn’t really guess it for a good reason). It’d be better though if we knew if someone had guessed 20 kt; I wish we knew the whole spread.

  2. [...] I’m interested in how nuclear explosions sound, and how people who saw them described them, and how people planning to use them thought they could be really used, how they sketched them on [...]

  3. […] long view of things. And as President of Harvard since 1933, he commanded a lot of academic clout. He was at the Trinity test. He and Bush bent Roosevelt’s ear about making the bomb, and later trying to control […]

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