Interview with Thomas A. Tombrello - Caltech Oral Histories

Tombrello–115
protons, you didn’t get much neutron-rich stuff. They designed this bomb, which had its own
problems, but it was, again, gun-assembled. It was longer. You needed higher velocity because
of the plutonium-240, but they figured they could get around it. There were some other
problems with the aerodynamic stability of this thing, which was called Thin Man. It tended to
rotate in a plane rather than falling like an arrow. But they figured they could work that out. But
when they got the first plutonium samples from the Hanford reactor, it had more 240 than the
previous sample from Berkeley, and they knew they couldn’t assemble a gun to make critical
mass. So almost immediately, they jumped into an implosion design, where you take something
that’s roughly spherical and you compress it with high explosives so it becomes a smaller sphere,
reaching critical mass that way.
ASPATURIAN: Seth Neddermeyer.
TOMBRELLO: I’m going to tell that story. I knew Seth.
ASPATURIAN: You knew him?
TOMBRELLO: Yes. I spent the summer once at the University of Washington, where he was at
the time. But my Los Alamos question was, When did Oppenheimer start the implosion project?
Because almost overnight, after they got those plutonium samples, they were doing implosion.
And the answer was, Probably about day one. Seth Neddermeyer had this idea of implosion and
had been given a tiny little room with, I think, five people to study implosion and do
experiments—not very successful experiments, but doing them. That’s when I realized
Oppenheimer was such a brilliant project manager. He anticipated a possible obstacle and he
started working on it early in the project—not when he hit the obstacle but long before. Now,
the interesting part of the story, from Neddermeyer’s point of view, and which Neddermeyer
never quite liked, was that once Oppenheimer saw that implosion might be a solution to the
critical-mass problem, that project went from five people to five hundred in a couple of days.
Neddermeyer became an advisor to George Kistiakowsky, who was appointed to run it. Here
Oppenheimer again showed the strength of a project manager, realizing that the person you had
for the wild card was not necessarily the person you needed to implement his idea. That was
truly brilliant.
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