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Sunday, December 2, 2007

CP-1


Sixty five years ago today (December 2, 1942), the world moved into a new and more dangerous era. CP-1 is the code designation for Chicago Pile-1, the first nuclear fission pile built in an abandoned squash court at the University if Chicago. Enrico Fermi and his colleagues who built the pile were part of the Manhattan Project. The goal was to develop an atomic bomb before the Germans did.

The experimental reactor was built under the abandoned west stands of Stagg Field stadium. The pile contained 771,000 pounds of graphite, 80,590 pounds of uranium ore, and 12,400 pounds of uranium metal. It was a crude affair about the size of a two-car garage. The pile was constructed quickly (but carefully) and was held together with a lumber frame to keep the massive weight of the sphere of bricks in place.

The physicists had been testing the pile all morning of December 2nd. Richard Rhodes in The Making of the Atomic Bomb describes the scene in the afternoon of that day:

At two in the afternoon they prepared to continue the experiment...Forty-two people now occupied the squash court, most of them crowded onto the balcony. Fermi ordered all but one of the cadmium control rods again unlocked and removed. He asked Weil to set the last rod at one of the earlier morning settings and compared pile intensity to the earlier reading. When measurements checked he directed Weil to remove the rod to the last setting before lunch, about seven feet out...'This time, he told Weil, 'take the control rod out twelve inches.' Weil withdrew the cadmium rod...'This is going to do it,' Fermi told Compton. The director of the plutonium project had found a place for himself at Fermi's side. 'Now it will become self-sustaining. The trace [on the recorder] will climb and continue to climb; it will not level off.'...Again and again the scale of the recorder had to be changed to accommodate the neutron intensity which was increasing more and more rapidly. Suddenly Fermi raised his hand. 'The pile has gone critical,' he announced. No one present had any doubt of it. Fermi allowed himself a grin. Its neutron intensity was then doubling every two minutes. Left uncontrolled for an hour and a half, that rate of increase would have carried it to a million kilowatts. Long before so extreme a runaway it would have killed anyone left in the room and melted down.

'Then everyone began to wonder why he didn't shut the pile off,' Anderson [a physicist present] continues. "But Fermi was completely calm. he waited another minute, then another, and then when it seemed that the anxiety was too much to bear, he ordered, 'ZIP in!' It was 3:53 PM. Fermi had run the pile for 4.5 minutes at one-half watt and brought to fruition all the years of discovery and experiment. Men had controlled the release of energy from the atomic nucleus.


Rhodes states that the decision to build the pile and run what could have turned into a runaway nuclear experiment akin to Chernobyl was left entirely to the project management. Even the president of the University was not informed. Fermi was not worried about an accident but this was the first critical fission reaction in history. Chicago might never have been the same.

Another Manhattan Project physicist, Leo Szilard, stayed behind with Fermi when everyone else had left after the celebrations and toasts. Rhodes quotes Szilard as saying:

There was a crowd there and then Fermi and I stayed there alone. I shook hands with Fermi and I said I thought this day would go down as a black day in the history of mankind.


Of course, subsequent events proved Szilard right. The nuclear genie had been released and it has never been put back in the bottle. We now live within the constant shadow of nuclear warheads. We go on our way, hardly thinking about the destructive power that can be unleashed. Clearly, nuclear fission also has a positive side: nuclear energy. But when do the cons outweigh the pros? If it is possible to develop a technology, must it be developed? Will it be developed, regardless? Do we really have the ability to control the technology we develop or are we inexorably driven by the newest discoveries in science? These are troubling questions. They ought to be troubling questions. Ultimately, are we in control of our own destiny?

It is a profound and necessary truth that the deep things in science are not found because they are useful; they are found because it was possible to find them.

- J. Robert Oppenheimer


[Image of atomic bomb exploding over Nagasaki, Japan, August 9, 1945]

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