After I got my PhD from Harvard in 1955, I needed a job and a friend made a suggestion: on the campus there was a relatively modest cyclotron, simple enough for graduate students to operate. There was a position open for a "house theorist." My friend recommended me and I got the job, but after two years my appointment was over and I had to look for a new job. I applied to the Institute for Advanced Study of Princeton and was accepted for autumn 1957. This left the summer.
The Livermore and Los Alamos weapons laboratories were actively recruiting. Ken Bainbridge, chair of the Harvard physics department, called me into his office and asked if I would like a summer job at Los Alamos. He said he would recommend me. Los Alamos for me had an almost mystic quality–and some extra money would come in handy when I got to Princeton. I spoke to a Los Alamos recruiter, who told me that I could have the job if I was able to get the relevant security clearance.
In 1947 the Atomic Energy Commission introduced a Personnel Security Questionnaire to determine levels of clearance. The levels were "P," then "S," then "Q." A person with Q clearance was entitled to information about nuclear weapons on a "need to know" basis. I had to supply the FBI with a list of everywhere I'd lived for the last ten years. I was rather worried about a great-aunt, who was a subscriber to the Daily Worker and spoke in dark tones about the "bosses." Either they overlooked her or decided she was harmless because I got my clearance.
I arrived at the guard station at Los Alamos and was fitted out with credentials. I discovered that I was sharing an office with Ken Johnson, whom I had known since graduate school. It soon became clear that no one had any work for us, so we were free to do whatever we wanted. I had come with a problem of how to determine the parity of the pi zero using aspects of its two photon decay. I was stuck on the mathematics, so we decided to do it together. Ken was a great mathematician and he proved results with a high degree of generality. We wrote a paper and submitted it to Carson Mark, the director of the theoretical division, to see if we could publish it with a Los Alamos imprimatur. Mark was pleased: he wanted Los Alamos to have a reputation as something other than a bomb factory.
Of course, it was a bomb factory. Los Alamos and Livermore were churning out designs for devices small enough to fit into intercontinental missiles. These were being tested above ground in Nevada in a series that was called Operation Plumbbob. We used to have afternoon tea–something Oppenheimer had introduced during the war–and I'm sure that most of the people who attended were working on weapons.
Francis Low was a consultant to the controlled nuclear fusion program. I had met him briefly when he'd been a visiting professor at MIT; after the summer he was returning there permanently. He was a hero of mine. He and Murray Gell-Mann had made a study of quantum electrodynamics at short distances that introduced techniques which are still basic to quantum field theory. In the middle of August, Francis announced he was going to be away watching bomb tests in Nevada. Surprised, I asked if he had been working on weapons. He said no but that Carson Mark had invited him to observe a test. I asked if there was any chance I could go too. Francis said I would have to ask Carson, who told me I could come along provided I paid my way. On the morning of 30 August the three of us took off from the small airstrip at Los Alamos on a commuter flight to Albuquerque.
I was about to enter the "need to know" world. I decided that under no circumstances would I ask any questions. I had no legitimate need to know. I had no idea of our itinerary. I knew that we would have to get from Las Vegas to Mercury, Nevada, the location of the test site, some 65 miles north-west of Las Vegas. That nuclear weapons were being exploded above ground–dumping thousands of kilocuries of radiation into the atmosphere–so close to a major city shows the craziness of the time. After we landed at Las Vegas and were met by a small delegation of Los Alamos people in a government car, a casino was our first stop.
The casino must have had a lot of business from people at the test site because there was a light that was turned on if the test scheduled for the next morning was on. The light came on, and we drove to Mercury for a few hours' sleep. The tests were scheduled for 5.30 a.m. That morning a device called Smoky was to be tested. Carson explained that it was a Livermore device. You could tell because they named their devices after mountains; Los Alamos devices were named after scientists. Galileo was in a tower being readied for a test in two days. We went to a concrete bunker to await the explosion. I was given some very dark glass to put over my own glasses. Even the reflection from the bunker walls could damage your eyes. I don't know how far away from the explosion we were but we were close enough to see the 700-foot tower that had the bomb on top of it.
A loudspeaker counted out the minutes until the explosion and then counted down the last sixty seconds. I had turned my back and covered my eyes with the dark glass but the bright flash still made me shut them. I counted to ten and then turned round.
The horizon in front of me was in turmoil. In the center was a livid red-orange cloud. The hugeness of it was what impressed me. I had had no idea of the sheer scale of a nuclear explosion. I felt a sharp and slightly painful click in my ears. This was the supersonic shock wave. Then came the sound: a sort of rolling thunder. The cloud had turned purple and black and hung in the air like a radioactive cobra about to strike. There was talk of taking cover, but it didn't move in our direction. I stood there mute. We went back to the dormitory to get a little more sleep.
Sometime around mid-morning we drove with Carson to the 500-foot tower where the next device, the Los Alamos Galileo, was going to be exploded. On the way there were spots in the desert where the sand had fused into glass. Signs were posted warning of high radioactivity from previous tests. We got to the base of the tower. You could ride most of the way to the top in an open elevator. From that point on there was only a rickety steel ladder. The desert looked a long way down. I had a moment of panic but then it occurred to me that at the top of the ladder there was a nuclear device with a yield comparable to the bomb that flattened Hiroshima. And I was worried about climbing a ladder?
The top was a flat space with just about enough room for Galileo and its attendants. It was a big device with various wires coming out and looked more like a diving bell than a bomb. There was a clicking noise from a vacuum pump. I had no idea why it was there and didn't ask. Carson spoke to the crew and we went back down the elevator. Carson then drove to a concrete blockhouse at the far edge of the site.
He walked in without knocking or ringing and we followed. Neatly arranged on shelves were the plutonium pits of a considerable number of atomic bombs, probably enough to destroy many cities. I stepped back towards the door. I had read enough about Hiroshima and Nagasaki to know what I was looking at. Carson picked up one of the pits, handed it to me, and told me not to drop it. It was warm to the touch–alpha particles–and about the size and weight of a bowling ball. I didn't know enough to ask the obvious question: why was it so light? A solid sphere of plutonium this size would have weighed a couple of hundred pounds. I'm sure that had I asked I wouldn't have got an answer. Even asking would have been viewed unfavorably. It was then that I noticed her.
At the other end of the building there was a large workbench where a man was filing something that looked to me like white putty. I had read enough to know that what looked like white putty was a high explosive which was going to be attached to the pit to cause the implosion of the plutonium sphere. Next to him a woman was knitting a green sweater. I don't mean to sound pretentious, but I at once thought of Eliot's "This is the way the world ends." What was she doing there? I didn't dare ask.
The next morning Galileo was tested. I now knew what to expect but was still overwhelmed. Then we returned to Los Alamos. None of us talked about the tests. Somehow I felt the experience had made me part of the secret world. If you like, I had learned to love the bomb.
Over the next years I came to realize how foolish I had been. The Plumbbob series, to which Smoky and Galileo belonged, were the biggest and longest series of tests ever done in the continental United States, 29 in all. The highest explosive yield was Hood, the test that took place on 5 July –the equivalent of 74 kilotons of TNT. The Nagasaki bomb was about 20 kilotons. Smoky was the second highest, with 44 kilotons equivalent. The series, during which the total yield was about 306 kilotons–something like a tenth of the yield of one hydrogen bomb–released about 58,300 kilocuries of radioiodine into the atmosphere. This fallout was distributed all over the United States and is estimated to have caused about 32,000 cases of thyroid cancer. Twelve hundred pigs were exposed to the explosions in blast-effect studies, and 18,000 servicemen also participated. Roughly 1200 watched the Smoky explosion from a distance of about 13 kilometers. A unit was flown to ground zero some 15 minutes later. They declared that it was safe to occupy so the rest were flown in twenty minutes after the explosion. The exercise was completed at 9:45 a.m. Some of these men later contracted leukemia.
The plutonium pit I was given to hold was so light because it was hollow. The weapons being tested that summer were "boosted": deuterium and tritium gas were injected into the cavity just before the explosion. I believe the vacuum pump I heard when we visited Galileo was connected to this. When the pit is imploded, and the density is increased enough to reach a supercritical mass, the fission chain reaction begins. When about 1 percent of the plutonium has been fissioned, the temperature is raised to the point where the fusion reactions of the deuterium and tritium take place. These produce a blast of very high-energy neutrons which boost the subsequent fission efficiency. That is what accounted for the large yields in some of the bombs tested that summer. There is no end to the ingenuity that was being applied to weapons design.
The last above-ground test by the United States took place in 1962, and the last above-ground test anywhere was conducted by China in 1980. This is certainly a good thing. But I have only one misgiving. No one has seen a nuclear explosion in more than thirty years and the number of people who have ever seen one is dwindling. For most people, nuclear weapons are an abstraction. Perhaps there should be one more explosion in the desert of Nevada to remind us.
Jeremy Bernstein is a physicist and author. He was for thirty five years a staff writer for The New Yorker and now writes frequently for the New York Review of Books.
This article is excerpted from "At Los Alamos: Learning to Love the Bomb" by Jeremy Bernstein, available from Now and Then at nowandthenreader.com. The unabridged version appeared originally in the December 20, 2012 issue of the London Review of Books (see www.lrb.co.uk ).