Posts Tagged ‘Nuclear testing’

Visions

Operation Crossroads at 70

Monday, July 25th, 2016

This summer is the 70th anniversary of Operation Crossroads, the first postwar nuclear test series. Crossroads is so strange and unusual. 1946 in general ought to get more credit as an interesting year, as I’ve written about before. It was a year in flux, where a great number of possible futures seemed possible, before the apparently iron-clad dynamics of the Cold War fell into place. Crossroads happens right in the middle of the year, and arguably made a pretty big contribution to the direction that we ended up going. Such is the subject of my latest article for the New Yorker‘s Elements blog, “America at the Atomic Crossroads.” Today is the anniversary of the Baker shot, which Glenn Seaborg dubbed “the world’s first nuclear disaster.”

America at the Atomic Crossroads

There are a lot of things that make Crossroads interesting to me. The bomb was still in the hands of the Manhattan Project. The Atomic Energy Act of 1946 had not yet been signed into law (Truman would sign it in August, and it would go into effect in January 1947), so the Atomic Energy Commission did not yet exist.

There were these amazing interservice rivalry aspects: the whole backdrop is a Navy vs. Army tension. The Manhattan Project, and the Army Air Forces, had gotten all the glory for the bomb. The Navy didn’t want to be left out, or seen as irrelevant. Hence them hosting a big test, and glorying in the fact that a Nagasaki-sized atomic bomb doesn’t completely destroy a full naval squadron. (Which was no surprise to anybody on the scientific or military side of things.)

The US had only about 10 atomic bombs at the time. So they expended about 20% of their entire nuclear arsenal on these tests, for relatively little military knowledge gained. The Los Alamos scientists were pretty lukewarm on the whole operation — it just didn’t seem like it was getting them much. One wonders, if the bomb had not still be under military control, whether it would have happened.

Photograph of the early mushroom cloud by LIFE photographer Frank Scherschel, with a darkened filter to compensate for the brightness of the flash. Source.

Photograph of the early mushroom cloud of Crossroads Able by LIFE photographer Frank Scherschel, with a darkened filter to compensate for the brightness of the flash. Source.

The first shot, Able, was something of a flub. The fact that it missed its target meant that for public relations purposes it was seen as very ineffective, but it also means that their scientific observations were largely pretty useless. In fact, it missed its target and blew up over one of the main instrumentation ships.

If you read most sources about Crossroads they will say that the source of the Able miss was undetermined, but if you dig down a little deeper you find some pretty plausible solutions (and the reason why the official verdict was “undetermined”). Paul Tibbets, the captain of the Enola Gay and overall head of the atomic delivery group, was pretty clear that it was human error. He said that even before the shot they realized that the crew of the B-29 which dropped it, Dave’s Dream, had gotten bad information about the weather conditions, but that they ignored attempts at correction. Tibbets would re-run (with a dummy bomb) the drop with the correct information (and got very close to the target), and also re-ran it with the wrong information (which missed by nearly the same amount as the Able shot). But the USAAF really didn’t want to throw their bombardier and plane crew under the bus. So they hinted it might be a problem with the ballistics of the weapon (which were indeed a bit tricky), which infuriated the Manhattan Project officials. Anyway, everyone seems to have been satisfied by just saying they couldn’t figure out where the error was. But Tibbets’ account seems most plausible to me.1

Crossroads was not secret operation, though there was much classified about it. There were full-spread articles about its purpose in national news publications both before and after its tests. There was probably no test series so publicly conducted by any nuclear power — announced well in advance, covered by the press in real-time, and then heavily publicized afterwards. The fact that the Soviets were invited to a US nuclear test operation (something that would not happen again until the late-1980s) opens up whole other dimensions.

Mikhail Meshcheryakov ("Mike"?) in 1946. At right he is on the USS Panamint, at the Crossroads test. Source: Mikhail Grigorivich Meshcheryakov, on the 100th-anniversary of his birth (Dubna, 2010).

Mikhail Meshcheryakov  in 1946. At right he is on the USS Panamint, at the Crossroads test. Source: Mikhail Grigorivich Meshcheryakov, on the 100th-anniversary of his birth (Dubna, 2010).

The Soviets had three observers at the test: Professor Semyon P. Aleksandrov, a geologist who had worked on the prospecting of uranium; Mikhail G. Meshcheryakov, an experimental physicist; and Captain Abram M. Khokhlov, who attended as a member of the international press corps (he wrote for the Soviet periodical Red Fleet). I found a really amusing little anecdote about the Soviet observers from one of the men who worked the Manhattan Project security detail on Crossroads: Aleksandrov was someone they knew already (he was a “dear old geologist”), but Meshcheryakov was someone “whose name was known, but no one had met personally leading some of us to support he was really an NKVD agent watching Aleksandrov.”

I found nothing in the Russian source materials (mentioned below) that would indicate that Meshcheryakov was NKVD, though he was definitely the one who wrote up the big report on Crossroads that was given to Beria, who summarized it for Stalin. Meshcheryakov’s report is not among the declassified documents released by the Russians, so who knows if it has any political commentary on Aleksandrov in it. Meshcheryakov ended up having a rather long and distinguished physics career in the USSR, though there is almost no English-language discussion of him on the Internet. Aleksandrov, the “dear old geologist,” was actually a major Soviet big-wig in charge of mining operations, which at that time meant he was high in the Gulag system, which was run by the NKVD. For what it’s worth.2

Radiation from the Crossroads Baker shot — the radiation went up with the cloud, and then collapsed right back down again with it, resulting in a very limited extent of radiation (the entire chart represents only 4.5 miles on each axis), but very high intensities. Chart source: DNA 1251-2-EX. Collapsed cloud picture source: Library of Congress.

Radiation from the Crossroads Baker shot — the radiation went up with the cloud, and then collapsed right back down again with it, resulting in a very limited extent of radiation (the entire chart represents only 4.5 miles on each axis), but very high intensities. Chart source: DNA 1251-2-EX. Collapsed cloud picture source: Library of Congress.

It was also something of the real birth of “atomic kitsch.” There are some examples from before Crossroads, but there is just a real flourishing afterwards. It seems to have taken a year or so after Hiroshima and Nagasaki for enough time to have passed for Americans to start to regard nuclear weapons entirely frivolously. With Crossroads in particular, a deep connection between sex and death (Freud’s favorites) circled around the bomb. This is where we start to see the sorts of activities that would later result in the “Miss Atomic Bomb” contests, the release of the really kitchy songs, and, of course, the Bikini swimsuit, named after the “atomic bomb island,” as LIFE put it.

The key fulcrum of my article is a meditation on the “crossroads” metaphor, and I should probably note that it was, to some degree, intentional. Vice Admiral William Blandy was reported by the New York Times to have told Congress, that the name was chosen for its “possible significance,” which the Times writer interpreted to mean “that seapower, airpower, and perhaps humanity itself — were at the crossroads.”3

An unusual color (but not colorized!) photograph of the Crossroads Baker detonation, from LIFE magazine. Source.

An unusual color (but not colorized!) photograph of the Crossroads Baker detonation, from LIFE magazine. Source.

What’s interesting to me is that Blandy clearly saw some aspects of the “crossroads,” but there was much he couldn’t have seen — the atomic culture, the arms race, the contamination, the nuclear fears. He knew that “crossroads” was a good name for what they were doing, but it was an even better name than he could have known, for both better and worst.


As before, I wanted to take a moment to give some credit/citation information that wasn’t workable into the New Yorker blog post (where space, and thus academic nicety, is constrained).

The best overall source on Crossroads, which I found invaluable, is Jonathan Weisgall’s Operation Crossroads: The Atomic Tests at Bikini Atoll (Naval Institute Press, 1994). Weisgall has been a legal counsel on behalf of the Marshallese, and his book is just a wealth of information. I was pleased to find a few things that he didn’t have in his book, because it’s a really tough challenge given how much work he put into it. If you find Crossroads interesting, you have to read Weisgall.

Rita Hayworth on the Crossroads Able bomb, "Gilda." Photo by Los Alamos National Laboratory, via Peter Kuran and Bill Geerhart.

Rita Hayworth on the Crossroads Able bomb, “Gilda.” Photo courtesy Los Alamos National Laboratory, via Peter Kuran and Bill Geerhart.

Bill Geerhart, who writes the excellent blog CONELRAD Adjacent (and is the one behind the Atomic Platters series of Cold War songs), has done some really wonderful work on the cultural aspects of Crossroads over the years. His posts on the mushroom cloud cake, and his sleuthing regarding the Rita Hayworth connection, are amazing and worth reading in their entirety. Peter Kuran, the visual effects wizard who made the documentary Trinity and Beyond, among other films and works, was very helpful in providing recently-declassified imagery of the Crossroads bombs, including photos (which I first saw on Geerhart’s blog) of the Rita Hayworth image on the side of the bomb themselves. (I will be writing more about Kuran and his work in the near future…)

Holly Barker’s Bravo for the Marshallese (Thomson/Wadsworth, 2004), is immensely useful as an anthropologist’s view of the Marshallese people and their experiences after the test. My invocation of the Marshallese language for birth defects comes directly from Barker’s book, pages 81 and 106-107. It is a powerful, disturbing section of the book.

Selection from Life magazine's coverage of Crossroads — two visions of the animal testing. Source.

Selection from Life magazine’s coverage of Crossroads — two visions of the animal testing. Source.

Most of the information I got about the Soviet view of Crossroads comes from the multi-volume Atomniy Proekt SSSR document series released by the Russian Federation. I had the full set of these before it was cool, but now Rosatom has put them all online. Scholars have been picking over these for awhile (I have written on them once before), I haven’t seen anybody use the particular documents relating to Crossroads before, but you in Tom (Volume) 2, Kniga (Book) 6, the documents I found most useful were 44 (pp. 130-132), 48 (135-136), 50 (137), 76 (184-188), and 106 (246-248). They show the picking of the delegation of observers, brief biographies of the observers, a summary of Meshcheryakov’s report (his full 110-page report on Crossroads is not included), and some later aspects of Meshcheryakov’s involvement with the planning of the first Soviet nuclear test in 1949 (in which his Bikini experience was offered up as his bonafides).

The other really unusual little source I used for my article is the letter from Percy Bridgman. The letter was sent from Bridgman to Hans Bethe, who relayed it to Norris Bradbury at Los Alamos, who sent it to General Groves. You can read it here. I have been sitting on it for a long time — I almost wrote a blog post about it in 2012, but decided not to for whatever reason. When I worked at the American Institute of Physics I had an opportunity to poke around Bridgman’s life and writings a bit, and he’s really an interesting character. He was the one at Harvard who served as J. Robert Oppenheimer’s physics advisor, and his own work on high-pressure physics not only won him the Nobel Prize of 1946 (which is a nice coincidence for the Crossroads article), but also was used (and is still classified, as far as I can tell) on the Manhattan Project (they seem to have sent him plutonium samples, so you can imagine the kind of work he was doing and why it might still be classified — almost everything on plutonium under high pressures is classified in the United States).

Percy W. Bridgman (L) talking with Harvard colleague (and future Trinity test director) Kenneth Bainbridge, 1934. Source: Emilio Segrè Visual Archives, American Institute of Physics

Percy W. Bridgman (L) talking with Harvard colleague (and future Trinity test director) Kenneth Bainbridge on a Massachusetts beach, 1934. Source: Emilio Segrè Visual Archives, American Institute of Physics.

Bridgman gave a number of talks associated with his Nobel Prize that really tried to get at the heart of what the effects of World War II would be for physics as a discipline. He was very much afraid that Big Science (which hadn’t yet been given that name) would really destroy work like his own, which he saw as small-scale, individual, and not focused on particular applications. He was also very interested in topics related to the philosophy of science, something that a lot of modern-day practicing physicists openly disdain. His Wikipedia page gives a nice, brief overview of his life, and even touches on the poignant circumstances of his death.4.

Notes
  1. This is discussed at length in Jonathan Weisgall’s Operation Crossroads, pp. 201-204. []
  2. The account of the security officer is Charles I. Campbell, A Questing Life: The Search for Meaning (New York: iUniverse, 2006). This appears to be a self-published memoir, the sort of thing one would never run across without Google Books. On Aleksandrov’s Gulag connections (which seem plausible given his uranium connections), see this page on his Hero of Socialist Labor award. One of the few English-language articles on Meshcheryakov is available here. []
  3. Sidney Shallet, “Test Atomic Bombs to Blast 100 Ships at Marshall Atoll,” New York Times (25 January 1946), 1. Blandy’s full quote on the name from the testimony: “The schedule of target dates for this operation, which will be known by the code word ‘CROSSROADS’—and I would like to explain that we have chosen that merely for brevity in dispatches and other communications, and we chose it with an eye to its possible significance—now calls for the first test to be accomplished early in May, over target ships at an altitude of several hundred feed.” A lot of the sources about Crossroads include Shallet’s bit about “perhaps humanity itself” as a quote of Blandy’s, but it’s not in the transcript that I can see. Hearing before the Special Committee on Atomic Energy, United States Senate, Pursuant to S. Res. 179, Part 4, 79th Congress, 2nd Session (24 January 1946), on 457. []
  4. The citation for the Bridgman letter is: Percy W. Bridgman to Hans Bethe, forwarded by Norris Bradbury to Leslie Groves via TWX (13 March 1946), copy in the Nuclear Testing Archive, Las Vegas, NV, document NV0128609. []
News and Notes

Rumbles from North Korea

Saturday, January 9th, 2016

This past week and this next week are the last of my winter break before the new semester starts, which in the true fashion of academia means I am more busy than I usually am trying to cram as much non-teaching “work” into every day as possible. North Korea’s test of a nuclear weapon earlier this week, of course, just added to the workload. Thanks, Kim Jong-un. I am behind on my annual Nuclear History Bibliography, but it is coming, soon. NUKEMAP usage has been about 10X higher than normal — over 300,000 users last week.

New Yorker - An H-bomb by Any Other Name

I have written up a piece for the New Yorker’s Elements blog on the historical-technical-political dimensions of calling something a “hydrogen bomb,” or disputing it, that went up yesterday. I also talked a bit to Business Insider about how the true “Teller-Ulam design” of a thermonuclear weapon is not merely a single bomb design but an entire system of designing a getting of possible effects — so one ought not necessarily be expecting the North Koreans to make something that looks like Ivy Mike, Castle Bravo, or, god forbid, the Tsar Bomba. The North Koreans themselves, in their official statement (a wild read in and of itself), claimed that the “technological specifications of the newly developed H-bomb for the purpose of test were accurate and scientifically verified the power of smaller H-bomb” — a lot of little qualifications that seem to be saying, “we’re trying for miniaturization, not high yields, and this was a scientific test of a principle, not of a full-yield warhead.”

Given their strategic situation, a smaller bomb would make a whole lot more sense than something the size of a school bus. And I would note that the tendency to test all weapons at full power (or even more than the projected yield) is something that, while characteristic of the American program, is not necessarily the only way to do things. (The Soviets typically tested large bombs at half-power, on purpose.)

The seismic waveform of the North Korean test.

The seismic waveform of the 2016 North Korean nuclear test, as detected by a station in Mudanjian, China. Click here to listen to it rendered as audio. Source: Incorporated Research Institutions for Seismology.

Which is just to say, I don’t think we (at least those of us in the unclassified world) quite have enough information to really parse out what the North Koreans were trying to do in that test. The yield estimates coming out — ranging from 6 to 30 kilotons or so — don’t sound like much, in and of themselves. But there’s still a lot we don’t know, and might not know.1

Somewhere in between hysterically overestimating North Korea’s capabilities and smugly underestimating them is some sort of middle ground, a place where we need to acknowledge that this is 60-year-old technology, and the sheer technical difficulty alone is probably not going to stop them from becoming a fully-fledged nuclear power.

Notes
  1. And there are also ways to reduce the seismic signature of nuclear tests — like setting off a test in the cavern created by a previous test. It isn’t clear what incentive North Korea would have in making their tests look smaller than they actually were, but, then again, there is much about their thinking that is not intuitive to those of us on the outside. So I’m not sure that’s a likely scenario, but I don’t think it can be ruled out as impossible. []
Visions

Trinity at 70: “Now we are all sons of bitches.”

Friday, July 17th, 2015

A quick dispatch from the road: I have been traveling this week, first to Washington, DC, and now in New Mexico, where I am posting this from. Highlights in Washington included giving a talk on nuclear history (what it was, why it was important) to a crowd of mostly-millennial, aspiring policy wonks at the State Department’s 2015 “Generation Prague” conference. A few hours after that was completed, an article I wrote on the Trinity test went online on the New Yorker’s “Elements” science blog: “The First Light of Trinity.”

The First light of Trinity

Being able to write something for them has been a real capstone to the summer for me. It was a lot of work, in terms of the writing, the editing, and the fact-checking processes. But it is really a nice piece for it. I am incredibly grateful to the editor and fact-checker who worked with me on it, and gave me the opportunity to publish it. Something to check off the bucket list.

On the plane to New Mexico, I thought over what the 70th anniversary of Trinity really meant to me. I keep coming back to the post-detonation quote of Kenneth Bainbridge, the director of the Trinity project: “Now we are all sons of bitches.” It is often put in contrast with J. Robert Oppenheimer’s more grandiose, more cryptic, “Now I am become death, destroyer of worlds.” Oppenheimer clearly didn’t say this at the time of test explosion, and its meaning is often misunderstood. But Bainbridge’s quote is somewhat cryptic and easy to misunderstand as well.

The badge photograph of Kenneth Bainbridge, director of the Trinity project. From a photo essay I wrote for the Bulletin of the Atomic Scientists two years ago.

The Los Alamos badge photograph of Kenneth Bainbridge, director of the Trinity project. From a photo essay I wrote for the Bulletin of the Atomic Scientists two years ago.

Bainbridge’s quote first got a lot of exposure when it was published as part of Lansing Lamont’s 1965 book, Day of Trinity, timed for the 20th anniversary of Trinity. Lamont interviewed many of the project participants who were still alive. The book contains many errors, which many of them lamented. (The best single book on Trinity, as an aside, is Ferenc Szasz’s 1984, The Day the Sun Rose Twice, by a considerable margin.) A consequence of these errors is that a lot of the scientists interviewed wrote letters to each other to complain about them, which means they also clarified some quotes of theirs in the book. Bainbridge in particular has a number of letters related to mixed up quotes, mixed up content, and mixed up facts from the Lamont book in his personal papers kept at the Harvard University Archives, which I looked at several years back.

One of the people Bainbridge wrote to was Oppenheimer. He said he wanted to explain his “Now we are all sons of bitches” quote, to make sure Oppenheimer understood he was not trying to be offensive:

The reasons for my statement were complex but two predominated. I was saying in effect that we had all worked hard to complete a weapon which would shorten the war but posterity would not consider that phase of it and would judge the effort as the creation of an unspeakable weapon by unfeeling people. I was also saying that the weapon was terrible and those who contributed to its development must share in any condemnation of it. Those who object to the language certainly could not have lived at Trinity for any length of time.

Oppenheimer wrote back, in a letter dated 1966, just a year before his death, when he was pretty sick and in a lot of pain. It said:

When Lamont’s book on Trinity came, I first showed it to Kitty; and a moment later I heard her in the most unseemly laughter. She had found the preposterous piece about the ‘obscure lines from a sonnet of Baudelaire.’ But despite this, and all else that was wrong with it, the book was worth something to me because it recalled your words. I had not remembered them, but I did and do recall them. We do not have to explain them to anyone.1

I like Bainbridge’s explanation, because it doubles back on itself: people will think we were unfeeling and terrible for making this weapon, which makes it sound like the people are not understanding, but, actually, yes, the weapon was terrible. I think you can get away with that kind of blanket condemnation if you’re one of the people instrumental in its creation.

The original map of fallout from the Trinity test. There are several more "hot spots" to the South and West than are in the later more simplified drawings of it. Click to see the entire map at full resolution.

The original map of fallout from the Trinity test. There are several more “hot spots” to the South and West than are in the later more simplified drawings of it. Click the image to see the entire map at full resolution.

I have been thinking about how broadly one might want to expand the “we” in his quote. Just those at the Trinity test? Those scientists who made the bombs possible? All of the half-million involved in making the bomb, whether they knew their role or not? The United States government and population, from Roosevelt on down? The Germans, the fear of whom inspired its initial creation? The world as a whole in the 1940s? Humanity as a whole, ever?

Are we all sons of bitches, because we, as a species of sentient, intelligent, brilliant creatures have created such terrible means of doing violence to ourselves, to the extremes of potential extinction?

This is probably not what Bainbridge meant, but it is an interesting road to go down. It recalls the recent discussions about whether we live in a new era of time, the Anthropocene, and whether the Trinity test should be seen as the marker of its beginning,

Notes
  1. Regarding Baudelaire, supposedly, according to Lamont, this was going to be the code that Oppenheimer used to tell Kitty that the test was a success: “If the test succeeded, he would send her a brief message, an obscure line from a sonnet by Baudelaire: ‘You can change the sheets.'” []
Visions

Mushroom clouds strange, familiar, and fake

Monday, December 1st, 2014

If you spend a lot of time on the history of nuclear weapons, you see a lot of mushroom clouds photographs. There were over 500 atmospheric nuclear tests conducted during the Cold War, and most of these were photographed multiple times. (There were over 50 dedicated cameras at the Trinity test, as one little data point.) The number of unique photographs of nuclear explosions must number in the several thousands.

Castle Romeo

And yet, most of the time we seem to reach for the same few clouds that we’ve always reached for. How many books, for example, have this shot of the Castle Romeo mushroom cloud on their cover? Romeo was an American H-bomb test from 1954, 11 megatons in yield. It gets used, however, for all sorts of things — like the Cox Report’s 1999 allegations about China stealing advanced (much lower-yield) thermonuclear warhead designs, or illustrating Soviet nuclear weapons, or illustrating (most incorrectly) nuclear terrorism (which would not look like this at all). It’s a great photo (dramatic, red, well-framed), but it’s not a generic mushroom cloud — it is a really high yield weapon, and arguably ought to only be used to illustrate very high yield weapons.

OK, I’m a pedant about this kind of thing. I get annoyed with poorly-used mushroom cloud photos, and repetitive photos, because there are just so many good options out there if the graphic designers in question would just search beyond the first thing that comes up when you Google “mushroom cloud.” But re-using known clouds is not as bad as, say, mistaking a fake, computer-generated mushroom cloud for a real one.

Fake Tsar Bomba

This photo is often labeled as the “Tsar Bomba” cloud and it is not even an actual photograph of a nuclear test — it is a CGI rendering, and not even a very good one. I don’t think you even have to be a nuke wonk to recognize that, and that people’s CGI-savvy would be better than this, but I guess not. An animated version is circulating on YouTube — the physics is all wrong regarding the fireball rise, the stem, etc., and the texturing is off. Apparently a lot of people have been fooled, though.1 There is film of the actual Tsar Bomba explosion, and one can readily appreciate how different it is.

The above photo is also sometimes labeled as the “Tsar Bomba,” and was recently featured on the cover a book about the British atomic bomb, labeled as a British thermonuclear weapon. It is actually a French nuclear weapon, specifically the test dubbed “Licorne,” a 914 kiloton thermonuclear shot detonated in 1970 at the Fangataufa atoll in French Polynesia. I do admit finding the confusion about this one amusing, especially when it is mislabeled as a British test. (As an aside: I do not blame authors for the photos on their book covers, because I know they often don’t have anything much to do with the cover images.)

There are actually four shots from this same test that I don’t think most people realize are of a sequence, showing first the brief condensation cloud that formed in the first 20 seconds or so (which exaggerates the width of the actual mushroom cloud, similar to the famous Crossroads Baker photograph), and then tracks the mushroom cloud as it rises. When you resize them to the same scale (more or less), you can see that they are not four different shots at all, just differently timed photographs of the evolution of a single shot’s mushroom cloud:

There is also a film of the test, though the quality isn’t that great. The whole sequence represents less that a minute of the bomb detonation; as I’ve noted previously, most of our photos of mushroom clouds are from the first minute or so after their detonation, and they can get pretty unfamiliar if you watch the cloud evolve for longer than that.

Other clouds that have gotten overused (in my opinion) include Upshot-Knothole Grable, Crossroads Baker, and Upshot-Knothole Badger.

Does it matter that we re-use, and sometimes mis-use, the same mushroom clouds over and over again? In a material sense it does not, because the people who use/misuse these clouds are really not using them to make a sophisticated visual or intellectual argument. Rather, they have chosen a “scary mushroom cloud” image for maximum visual effect. And these fit the bill, except maybe the fake one, which will turn off anyone who can spot a fake.

But it does represent the way in which a lot of our cultural understanding of nuclear weapons has stagnated. The same visuals of the bomb, over and over again, mimic the same stories we tell about the bomb, over and over again. Culturally, there is a deep “rut” that has been carved in how we talk and think around nuclear weapons, a sort of warmed-over legacy of the late Cold War. I am sometimes astounded by how deep, and how deeply held, this rut is — on Reddit, for example, people will fight vehemently over the question of dropping of the atomic bomb, sticking exclusively to positions that were argued about 20 years ago, the last time this stuff was “hot.” They aren’t aware that the historiography has moved quite a distance since then, because you’d never know that from watching or reading most historical discussions of the bomb in mainstream media.

One of the first commercial uses of a fiery mushroom cloud to sell something unrelated to mushroom clouds — in this case, Count Basie's 1958 album, Basie.

One of the first commercial uses of a fiery mushroom cloud to sell something unrelated to mushroom clouds — in this case, Count Basie’s 1958 album, Basie. The test is Operation Plumbbob, shot Hood.

Fortunately, I think, these obvious ruts paradoxically create new opportunities for people who want to educate about the bomb. It is one of the ironies of history that the more firmly entrenched an existing narrative gets, the more interested people are in compelling counter-narratives. The fact that there is a rut in the first place means that there is already a built-in audience (as opposed to history that people just don’t know anything about), and if you can find something new to say about that history, then they’re interested.

“New” here can also mean “new to them,” as opposed to “new to people who spend their lives looking at this stuff.” This is what I was talking about when I was quoted in the New York Times a few weeks ago — things that known to scholars are being discovered and re-discovered by mass audiences who are surprised to find how many different and apparently novel photographs and stories are out there.

As an aside, if I were going to give graphic designers a set of “mushroom cloud use guidelines,” they would be, more or less: 1. don’t use the first cloud you find (there are so many unusual and dramatic ones out there, if you poke around a little bit); 2. don’t use extremely historically-specific clouds (i.e. Hiroshima and Nagasaki) as generic images; 3. don’t use multi-megaton shots (i.e. giant red/orange/yellow cloud fireballs) if you are talking about kiloton-range weapons (i.e. terrorist bombs); and 4. if you are going to label something as British, make sure it is not actually French!


Untitled

As part of my annual contribution to people becoming better acquainted with “new” mushroom cloud photographs, I have released a new and updated version of my Nuclear Testing Calendar for 2015. It features 12 unusual photographs of nuclear detonations, all of which I have carefully cleaned up to remove scratches and dust spots. All of the images are courtesy of Los Alamos National Laboratory.

Here is a little preview of some of the unusual clouds you will find in this calendar:

2015 Nuclear Testing Calendar preview

There are also over 60 nuclear “anniversaries” noted in the calendar text itself. And because 2015 is the 70th anniversary of the Trinity test, I have also reissued last-year’s Trinity test calendar. Both calendars are being offered for $18.99. The site that publishes them, Lulu.com, also often has a lot of coupons on a regular basis — please feel free to take advantage of them! All proceeds go to offsetting the costs of my web work. More details about the calendars and other nuclear delights at my updated Calendars, gifts, tchotchkes page.

Notes
  1. It seems to have been made by whomever made this webpage, who seems to say (if Google Translate is to be trusted), that it was rendered using the volumetric rendering software AfterBurn. []
Redactions

The Fat Man’s uranium

Monday, November 10th, 2014

What a long set of weeks it has been! On top of my usual teaching load (a few hours of lecture per week, grading, etc.), I have given two public talks and then flown to Chicago and back for the annual History of Science Society meeting. So I’ve gotten behind on the blog posting, though I have more content than usual for the next few weeks built up in my drafts folder, without time for me to finish it up. During this busy time, by complete coincidence, I also got briefly interviewed for both The Atlantic (on plutonium and nuclear waste) and The New York Times (on the apparent virality of nuclear weapons history).

Louis Slotin and Herb Lehr at the assembly of the Trinity "Gadget." Source: Los Alamos National Laboratory Archives, photo TR-229.

Louis Slotin and Herb Lehr at the assembly of the Trinity “Gadget.” Source: Los Alamos National Laboratory Archives, photo TR-229.

The Times article had a phrase in it that has generated a few e-mails to me from a confused reader, so I thought it was worth clarifying on here, because it is actually an interesting detail. It is one of those funny phrases that if you knew nothing about the bomb you’d never notice it, and if you knew a good deal about the bomb you’d think it was wrong, but if you know a whole lot more than most people care to know unless they are serious bomb nerds you actually see that it is correct.

Here’s the quote:

First, he glanced at the scientists assembling what they called “the gadget,” a spherical test device five feet in diameter. Then, atop a wooden crate nearby, he noticed a small, blocky object, nondescript except for the role he suddenly realized it played: It was a uranium slug that held the bomb’s fuel. In July 1945, its detonation lit up the New Mexican desert and sent out shock waves that begot a new era.

I’ve added emphasis to the part that may seem confusing. The Trinity “Gadget” and the Fat Man bomb, as everyone knows, were fueled by fission reactions in a sphere of plutonium. The Little Boy bomb dropped on Hiroshima, by contrast, was fueled by enriched uranium. So what’s this reference to a uranium slug inside the Trinity Gadget? Isn’t that wrong?

Detail from the above photo showing the tamper plug cylinder. Inset is a rare glimpse of what the tamper probably looked like, taken from a different Los Alamos photo related to Slotin's criticality accident. (It is in the middle-right of the linked photo. Yes, I cop to spending time searching the edges of photos like this for interesting things...) You can see how the tamper plug, rotated, would be inserted into the middle of the tamper sphere.

Detail from the above photo showing the tamper plug cylinder. Inset is a rare glimpse of what the tamper probably looked like, taken from a different Los Alamos photo related to Slotin’s criticality accident. (It is in the middle-right of the linked photo. Yes, I cop to spending time searching the edges of photos like this…) You can see how the tamper plug, rotated, would be inserted into the middle of the tamper sphere.

Perhaps surprisingly — no, it’s not. There was uranium inside both the “Gadget” and Fat Man devices — in the tamper. The tamper was a sphere of uranium that encased the plutonium pit, which itself encased a polonium-beryllium neutron source, Russian-doll style. Here uranium was chosen primarily for its physical rather than its nuclear properties: it was naturalunenriched uranium (“Tuballoy,” in the security jargon of the time), and its purpose was to hold together the core while the core did its best to try and explode. (It also helped reflect neutrons back into the core, which also worked to improve the efficiency.)

The inside of an exploding fission bomb can be considered as a race between two different processes. One is the fission reaction itself, which, as it progresses, rapidly heats the core. This heating of the core, however, causes the core to rapidly expand — the core is trying to blow itself apart. If the core expands beyond a certain radius, the fission chain reaction stops, because the fission neutrons won’t find further plutonium nuclei to react with. If you are a bomb designer, and want your bomb to have a pretty big boom, you want to hold the bomb core together as long as possible, because every 10 nanoseconds or so you can hold it together equals another generation of fission reactions, and each generation releases exponentially more energy than the previous.1

An image that somewhat evokes how bomb designers talk about the dueling conditions inside of the bomb, when they are talking to each other. The "snowplow region" is where the expanding bomb core runs into the tamper and is compressing it from the inside. This is a level of bomb design that I would have normally assumed would be classified but it has been very clearly declassified here, so I guess not. From Glasstone, "Weapons Activities of Los Alamos, Part I" (see footnotes).

An image that somewhat evokes how bomb designers talk about the dueling conditions inside of the bomb, when they are talking to each other. The “snowplow region” is where the expanding bomb core runs into the tamper and is compressing it from the inside. This is a level of bomb design that I would have normally assumed would be classified but it has been very clearly declassified here, so I guess not. From Glasstone, “Weapons Activities of Los Alamos, Part I” (see footnotes).

So in the Fat Man and Trinity bombs, this is accomplished with a heavy sphere of natural uranium metal. Uranium is heavy and dense, and the process of making plutonium and enriched uranium required the United States to stockpile thousands of tons of it, so the relatively small amount needed for a tamper was easily at-hand. It makes a good substance with which to try and hold an exploding atomic bomb together. The Little Boy bomb, as an aside, used a tungsten tamper, for some reason (maybe to avoid excessive background neutrons, I don’t know).

Now to add one more little bit of detail: we tend to think of the Trinity/Fat Man implosion bombs as just being a set of spheres-inside-spheres. This is a convenient simplification of the actual geometry, which had other factors that influenced it. The tamper, for example, was not just two halves of a hollow sphere that could fit together. Rather, it was more like a solid sphere out of which a central cylinder had been removed. The cylinder was known as the “tamper plug,” and was itself made of two halves that, when assembled, had room for the plutonium pit inside of them.

Why do it this way? Because the scientists and engineers wanted to be able to insert the fissile pit portion into the bomb as one of the final additions. This makes good sense from a safety point of view — they wanted it to be relatively easy to add the final, “nuclear” component of the bomb and to keep it separate from the non-nuclear components (like the high explosives) as long as possible. I don’t want to over-emphasize the “ease” of this operation, because it was not a quick, last-minute action to put the pit inside the bomb. (Some later bomb designs which featured in-flight core insertion were designed to be just this, but this was some years away.) It was still a tetchy, careful operation. But they could assemble the entire rest of the tamper, pusher, and high explosives, then remove one layer of high explosives, remove the top of the pusher, and then lower the tamper plug (with pit) into the center, then replace all of the other parts, hook up the detonators and electrical system, and so on.

A rendering I made in Blender to illustrate the principle here. The pit and initiator are inside of the plug (expanded at right), which is then sealed into a cylinder and inserted into the tamper sphere at the center of the bomb. The tamper is itself embedded in a boron shell which is inside of an aluminum shell which is inside of the explosive lenses which is inside of the casing. This is part of a modeling/visualizing project I've been working on for a little while now and will post more on at a future date. 

A rendering I made in Blender to illustrate the principle here. The pit and initiator are inside of the plug (expanded at right), which is then sealed into a cylinder and inserted into the tamper sphere at the center of the bomb. The tamper is itself embedded in a boron shell which is inside of an aluminum shell which is inside of the explosive lenses which is inside of the casing. This is part of a modeling/visualizing project I’ve been working on for a little while now and will post more on at a future date. The dimensions are roughly correct though there are still many simplified detail (e.g. exactly how the plug fits together — there were uranium screws!).

So when John Coster-Mullen describes, as in the previously-quoted New York Times article, finding a picture of the tamper plug, it’s kind of a cool thing. There’s only one picture that shows it (the one at the beginning of this post), and it is one of those things that you don’t even usually notice about that picture until someone points it out to you. I never noticed it until John pointed it out for me, even though I’d seen the picture many times before. Usually one’s attention is drawn to the Gadget sphere itself, and the people standing around (including Louis Slotin, who would later be killed by playing with a core). It’s kind of surprising it was declassified, since the length of the tamper plug is the diameter of the tamper, and the width of the plug is just a little bigger than the diameter of the plutonium core. The US government usually doesn’t like to reveal, even inadvertently, those kinds of numbers.

There is also one little fact about the natural uranium in the Gadget and Fat Man bomb that is not well appreciated, and I didn’t appreciate well until reading John’s book. (Which I have heard people say is rather expensive for a self-published production, but if you’re a serious Manhattan Project geek it is hard to imagine how you’d get by without a copy of it — it is dense with technical details and anecdotes. It is one of the only books that I don’t often bother to put back in the bookcase because I end up needing to reference it every week or so.)

Neutron cross-sections for the fissioning of uranium and plutonium. The higher the cross-section, the more likely that fission will occur. (Not shown on here is the competing capture cross-section, which matters a lot for U-238.) The indicated "fission neutron energy" means that that is the approximate energy level of neutrons released from fission reactions. So you can see why, in a reactor, those are slowed down by the moderator to increase the likelihood of fissioning. In a bomb, there is no time for slowing things down, so you need much more fissile material in much higher concentrations. Source: World Nuclear  Association.

Neutron cross-sections for the fissioning of uranium and plutonium. The higher the cross-section, the more likely that fission will occur. The indicated “fission neutron energy” means that that is the approximate energy level of neutrons released from fission reactions. So you can see why, in a reactor, those are slowed down by the moderator to increase the likelihood of fissioning. In a bomb, there is no time for slowing things down, so you need fissile material in much higher concentrations. Source: World Nuclear Association.

In talking about which elements are fissile — that is, can sustain a nuclear fission chain reaction — technical people tend to talk about neutron cross sections. This just means, in essence, that the likelihood of a giving elemental isotope (e.g. uranium-235, plutonium-239) undergoing fission when encountering a neutron is related to the energy of that neutron. At the size of neutrons, energy, speed, and temperature all considered to be the same thing. If you look at a neutron cross section chart, like the one above, you will see that uranium-235 has a high likelihood of fissioning from slow neutrons, and a low-but-not-zero likelihood of fissioning from faster neutrons. You will also see that the neutrons released by fission reactions are pretty fast. This is why to sustain a chain reaction in uranium you either need to slow the neutrons down (like in a nuclear reactor, which uses a moderator to do this), or pack in so many U-235 atoms that even the low probability of fissioning from fast neutrons doesn’t mean that a chain reaction won’t happen (like in a nuclear bomb, where you enrich the uranium to be mostly U-235).

Still with me? If you look a little further on the graph, you’ll see that uranium-238 also has a possibility of fissioning, but it is a pretty low one and only even becomes possible with pretty fast neutrons. This is why, in a nutshell, that unenriched uranium can’t power an atomic bomb by itself: it is fissionable but not fissile, because it can’t reliably take fission neutrons and turn them into further fission reactions. But people who have studied how thermonuclear weapons are used know that even uranium-238 can contribute a lot of explosive energy, if it is in the presence of a lot of high-energy neutrons. In a multistage hydrogen bomb, at least 50% of the final explosive energy is derived from the fissioning of U-238, which is made possible by the high-energy neutrons produced from the nuclear fusion stage of the bomb (which itself is set off by an initial fission stage). The neutrons produced by deuterium-tritium fusion are around 14 times more energetic than fission neutrons, so that lets them fission U-238 easily. From the cross-section chart above, you can see that U-238 fissioning can happen from fission neutrons, but only if they happen to be pretty high energy to begin with and stay that way. In practice, neutrons lose energy rather quickly. Still, according to a rather sophisticated analysis of the glassified remains of the Trinity test (“Trinitite”) done a few years back by the scientistsThomas M. Semkow, Pravin P. Parekh, and Douglas K. Haines, a significant portion of the final fissioning output at Trinity (and presumably also Nagasaki) came from the fast fissioning of the tamper, with some of that energy released from the U-238 fissioning.2

For the hardcore bomb geeks, here is a sort of "conclusion table" from the Semkow et al. article. Note that they calculate at least 30% fissioning from uranium, and give some indication the amount of compression of the core, the number of neutrons created, and so on.

For the hardcore bomb geeks, here is a sort of “conclusion table” from the Semkow et al. article. Note that they calculate at least 30% fissioning from uranium, and give some indication the amount of compression of the core, the number of neutrons created, and so on. Their terminology of the “eyeball” is taken from Richard Rhodes, who uses the term in passing in The Making of the Atomic Bomb, and refers to the confined area where the fission chain reaction is taking place.

How significant? Semkow et al. calculate that about 30% of the total yield of the Trinity test came from fissioning of the uranium tamper, which translates to about 6 kilotons of energy. If they had made the tamper out of tungsten (as was the Little Boy tamper), then the total yield of the Gadget would have only been around 14-15 kilotons — not that different from Little Boy (which was ~13-15 kt). And presumably if the Little Boy bomb had used a uranium tamper, assuming that didn’t cause problems with the design (which it probably would have, otherwise they probably would have used one), it would have had the same yield. (This doesn’t mean that Little Boy wasn’t, in fact, horribly inefficient — it got about the same yield but it required 10X the fissile the material to do so!) The total mass of the tamper was around 120 kg of natural uranium, so if it contributed 6 kilotons of yield that means around 350 grams of the tamper underwent fission, and that is about 0.3% of the total mass.3

So the fact that Trinity and Fat Man had uranium inside of them is already kind of interesting, but the fact that a large portion of the blast derived from that uranium is sort of a neat detail. Why don’t we generally learn about this? It isn’t that it is so terribly classified, per se, but it does require a lot of detailed explanation, as evidenced by the length of this post. We tend to abstract the mechanics of the bombs for explaining their conceptual role, and explaining the basic concepts of how they work. I have no problem with this, personally, because hey, let’s be honest, the exact amount of energy derived from different types of fissioning in the bombs is a pretty wonky thing to care about! But every once in awhile you need to understand the wonky things if you want to talk about, say, what that funny little “plug” is in the top-most photograph, and its role in the bomb. I suppose one of the points of the phenomena described by the Times article, where the geek population on the Internet is providing a newfound audience to Manhattan Project details, is that these sorts of wonky aspects are no longer limited to people like John Coster-Mullen, Carey Sublette, or myself. There are some people who might see this focusing on the technical details as missing the broader picture. I don’t happen to think that myself — much of the broader picture is in fact embedded in the technical details, and “new” discussions of technical details are one way of shaking people out of the calcified narratives of the Manhattan Project, something which, as we approach the 70th anniversary of Hiroshima and Nagasaki, seems to me a valuable endeavor.

Notes
  1. Calculating the efficiency of the bomb as a function of how well you can hold it together is apparently the essence of the still mostly-classified Bethe-Feynman formula. It is described qualitatively in Samuel Glasstone, “Weapons Activities of Los Alamos Scientific Laboratory, Part I,” LA-1632 (January 1954), 34-37. My copy of this report comes from the NNSA’s FOIA Reading Room. I downloaded the file in 2009, and sometime since then all of their PDFs have gotten corrupted somehow, and so many of the pages of the PDFs now available on their site are unreadable. For those who are curious, at a technical level, the corruption involved a systematic stripping out of the carriage return (0D) ASCII characters from the PDFs — there are none in any of the files, and there should be several thousand of them. Here is a screenshot from a hex editor showing the corrupted file (on left) versus the uncorrupted one (on the right). There seems to be no easy fix for this problem. I have tried to contact the NNSA about this but have gotten no response. It is one of many troubling incidents revealing, in my view, the very low priority that public release of information, and poor understanding of public-facing information technology, with regards to the present nuclear agencies. []
  2. Thomas M. Semkow, Pravin P. Parekh, and Douglas K. Haines, “Modeling the Effects of the Trinity Test,” Applied Modeling and Computations in Nuclear Science, ACS Symposium Series (American Chemical Society: Washington, DC, 2006), 142-159. The authors do not estimate the amount of tamper energy to have been released from U-238 fissioning as opposed to U-235 fissioning. []
  3. A 120 kg tamper of natural uranium ought to contain around 840 grams of U-235 in it, as an aside, which if that all fissioned at once would release around 14 kilotons of energy. The rule of thumb for uranium is that every kilogram which fissions releases about 17 kilotons. []