It was on this day in 1942 that scientists working on the Manhattan Project at the University of Chicago conducted the first-ever man-made nuclear reaction. The leader of the experiment was the Italian immigrant Enrico Fermi, who had won a Nobel Prize for discovering fission. He had realized that if you split an atom with a neutron, the split atom would produce more neutrons, which could then split other atoms, and so on, creating a chain reaction. To test the idea, he and his assistants built a makeshift nuclear reactor on an unused squash court near the university's football field, constructing a pile of uranium bricks interspersed with graphite blocks to slow down the neutrons. They used neutron-absorbing cadmium rods to delay the reaction until they were ready. A couple of young physicists stood on a scaffold over the pile with buckets of liquid cadmium as an emergency measure in case there was a meltdown.
Enrico Fermi
They started the reaction at 9:45 a.m., withdrawing all the cadmium rods so that the uranium neutrons would begin splitting atoms. The only way they could observe what was happening was with their Geiger counters, which measured the number of neutrons in the room. As the rods were removed, the Geiger counters made a clicking sound that grew faster and faster, until they began to make a sound that one of the eyewitnesses described as a roar. Finally, Fermi announced that the reaction had reached critical mass, and they reinserted the rods to shut it down. People applauded, but nobody cheered. They celebrated with paper cups of Chianti, but nobody made a toast. One of the young physicists there that day said, "We had known that we were about to unlock a giant; still, we could not escape an eerie feeling when we knew we had actually done it."
No comments:
Post a Comment