We Go for the Super
Since February 2021, I have been posting weekly entries on nuclear weapon matters—history and technology, and “secrets”—in You Might Want to Know on Substack. To see other entries, go to the You Might Want to Know Archive.
In September 1949, President Truman announced, to widespread alarm in this country, that the Soviets had successfully tested their first fission bomb. Turned out it was a copy, a very close copy, of the bomb we had dropped on Nagasaki. Probably with a few improvements the Soviet scientists and engineers had come up with.
On January 31, 1950, five months after President Truman made that announcement, he had made another one: we were going to try to build a Super bomb, a bomb that would be hundreds, maybe thousands of times more powerful than the single bombs we had used to destroy the cities of Hiroshima and Nagasaki.
Already, since even before the Manhattan Project began, a Hungarian-American physicist named Edward Teller had been trying to come up with such a bomb. Teller was a good physicist, but he kept not being able to figure out how to make the thing work. After all this time, more than ten years, there was reason to think it couldn’t be done.
But then, in February 1951, a year after President Truman’s announcement that we would be trying to build a Super bomb, a Polish-American physicist-mathematician named Stanislav Ulam, working at the time at our nuclear weapons laboratory at Los Alamos, had a flash.
Teller, who was also at Los Alamos at the time, jumped on Ulam’s idea. He was able to add some features. (There’s been quite a lot written on just who thought up what features of the Super and when; it seems clear we’ll never know all this with certainty, if that matters. It clearly mattered to Teller.)
For quite a while, it had been accepted that a Super’s “trigger” would have to be a fission bomb like the one used on Nagasaki. Nothing else could create the astonishing amount of heat and pressure—a heat and pressure greater than anything ever on earth before—that would be needed to start fusion going in the isotopes of hydrogen that would be the fusion fuel in the “hydrogen” bomb. The fusion is what would allow us to turn the fission bomb into a Super bomb, which was sometimes called a “fusion” bomb.
Actually, we’d already found a way to generate fusion that would add to the yield of a fission bomb. On May 25, 1951, in Operation Greenhouse out at our Pacific Proving Ground, in a nuclear bomb test called “Item,” we had shown that if we injected an isotope of hydrogen called tritium into the hollow center of a fission bomb just before it was imploded, the incredible heat and pressure at the center of the fission bomb’s imploding-and-then-exploding pit would produce fusion in the injected tritium and “boost” the yield of the bomb.
By quite a lot. “Item” yielded 45.5 kilotons, more than three Hiroshimas.
In such “boosted” weapons, the fission and fusion at the center of the pit generated almost instantly energy that quickly “disassembled” the fission fuel. After millionths of a second, the fission and the fusion would both stop. For the Super, the challenge was how to keep fusion going in a larger amount of fusion fuel for long enough to cause the release of a whole lot more energy along with highly energetic neutrons that would be able to cause cause more fission in uranium that might have been placed in and around the fusion fuel.
Ulam had realized that the X-ray radiation released by the detonation of the “primary” fission bomb might be used to create a plasma (an ionized gas), almost instantaneously, from some inert material that had been placed around a “secondary” filled with isotopes of hydrogen. The plasma would then heat and compress the secondary enough and for long enough to start and sustain fusion in the hydrogen. The bomb would be, then, you could say, “staged.”
There was more. A “spark plug” of fission fuel could be run down the center of the secondary that would be imploded by the pressure from the plasma and itself explode. That explosion would create, from the inside out, more heat and pressure on the compressed fusion fuel in the secondary.
The high energy neutrons generated by the fusion could then fly out and generate fission in any uranium that might have been blanketed around the secondary, even if the blanket were made of ordinarily inert non-fissile U238.
So the Super wouldn’t be just a fusion bomb, or a “hydrogen” bomb. It would be a fission-fusion-fission bomb. Fission in the very heavy elements of uranium and plutonium in a fission bomb would be the trigger. The fusion fuel would be isotopes of hydrogen—the lightest element—in a “secondary,” with high energy neutrons from the fusion causing more fission in fissile fuel that had been placed in and around the secondary.
Fission produces “fission products” that are radioactive. Fusion does not produce fission products. The primary would, therefore, always produce fission products, and so would the fission in the “spark plug,” if you had put one of those in the secondary. The neutrons from the fusion in the secondary might produce more fission products by causing fission in fissile material that had been blanketed around the secondary. So you could make these “hydrogen” bombs much more powerful, and also “dirtier,” by putting in them the spark plugs and the blankets of fissile material.
The “dirty” models would of course be much more widely lethal eventually but you wouldn’t be able to know in advance exactly where or when. Because you couldn’t calculate this in advance, the effects of residual radioactivity were often ignored in calculations of a bomb’s effects. We tended to consider only the “explosive yield.” Even though we knew that the effects of residual radioactivity would be massive and long-lasting.
That could be misleading, couldn’t it?
The breakthrough design I’ve just told you about came to be called the Teller-Ulam design. Which had to have pleased Teller. Even if that was the wrong way around, and Ulam was who had had the breakthrough.
When asked in late 1949 whether we should try to develop the Super bomb, the General Advisory Committee of the Atomic Energy Commission had opposed the project on moral and policy and practical military grounds, but also because it wasn’t certain the thing could be made to work. Now that Ulam’s technical solution seemed to have been arrived at—a solution that Oppenheimer himself called “sweet”—the GAC and the AEC got behind the project, which President Truman had already approved.
Might as well, I guess. Though that left the moral and policy and even the practical military problems still unaddressed.
The physicist at Los Alamos who was put in charge of building the test device was Richard Garwin.
Not Edward Teller.
Teller was a theorist, not an engineer. Garwin had been active in building the first fission bomb. During the Manhattan Project, Teller had refused to work on the fission bomb. He had kept working, unsuccessfully, on the Super.
Teller might have thought that at Los Alamos, he wasn’t getting the respect he deserved. In February 1952, he left Los Alamos to go to the Met Lab at the University of Chicago. Several months later, on September 2, 1952, he left the Met Lab and joined Ernest Lawrence at the Radiation Lab at the University of California at Berkeley. The plan was to start a second nuclear weapons laboratory in Livermore, thirty-seven miles south of Berkeley. It wasn’t entirely clear why we needed a second weapons lab. Maybe it was thought that the competition—an internal arms race—would be a good thing. In any case, Lewis Strauss, President Eisenhower’s new appointee to direct the Atomic Energy Commission, must have approved the plan for a second weapons lab.
Lawrence had invented in the 1930’s, at Berkeley, what he called a “cyclotron.” It was a big circular machine that used electromagnets to accelerate charged atomic particles to very high energies. The particles were then made to collide with each other. This changed their atomic properties. It had allowed the production of radioactive isotopes for medical uses. It had also led to the discovery of new elements, among them, plutonium—the “other” fissile fuel. PU was even more fissile than U235. Plutonium had been used in the bomb dropped on Nagasaki.
Plutonium’s discoverer, the chemist Glenn Seaborg, had at first named it “pandemonium.” Then, I guess, thought better of it.
In the early 1940’s, when Lawrence was working at Oak Ridge in the Manhattan Project, he had contributed an idea for how to enrich uranium that used electromagnets to accelerate charged particles in big machines he called “calutrons.” The calutrons hadn’t worked very well. A process called “gaseous diffusion” worked better. But it was still slow. We were trying everything to get enough highly enriched uranium to make an atomic bomb. Which we managed to do just before we used the bomb on Hiroshima.
The calutrons were retired soon after the war. Gaseous diffusion would be the way it would be done now, unless we could come up with something better.
Lawrence had, all along, like Teller, been a strong supporter of the Super. Maybe Teller would get more respect at Lawrence Radiation Laboratory.
Maybe also the scientists at Livermore would be less of a political pain than the ones at Los Alamos had turned out to be after the war in their urgings about the need to find a way to achieve international control of atomic energy.
Next: The First Tests of the Super