December 2, 1942: Enrico Fermi and atomic Chicago

The story begins with a letter from Albert Einstein to Franklin D. Roosevelt in 1939. The celebrated physicist warned the president that Nazi Germany was developing the makings of an atomic bomb.

Roosevelt knew what would happen if Hitler got such a weapon. The president ordered a massive secret project to make sure the U.S. beat him to it. Scientists from all over the country were enlisted in the effort.

Early in 1942 Enrico Fermi and a team of physicists gathered at the University of Chicago's Metallurgical Laboratory. Their goal was to develop a self-sustaining nuclear pile. This was the first step needed to produce the bomb.

Put simply, the scientists would arrange graphite blocks and uranium pellets in a certain way. Since nobody knew what would happen when the pile was finished, control rods were inserted as a safety measure.

A new lab for the project was being built in suburban Argonne. Then the construction workers went on strike. Fermi decided to push ahead without delay, using a room under the stands of Stagg Field, the university's unused football stadium. Since the university president probably would have vetoed the location, he was not told about it.

There was a great deal of theorizing, calculating, discussing, and changing of plans. There was a great deal, too, of piling and repiling of graphite bricks, hence the name pile for the uranium reactor. On the final day of trial Fermi, Compton, Zinn, and Herbert Lawrence Anderson (1914-1988) stood in front of the control panel located on a balcony ten feet above the floor of the court. Here stood George L. Weil (1908-1995), who was to handle the final control rod which held the reaction in check until it was withdrawn the proper distance. Another safety rod, automatically controlled, was placed in the center of the pile and operated by two electric motors which responded to an ionizing chamber. When a dangerously high number of neutrons were escaping, the gas in the ionizing chamber would become highly electrified. This would automatically set the motor operating to shoot a neutron-absorbing, cadmium-plated steel rod into the pile. As an added precaution an emergency safety rod call Zip was withdrawn from the pile and tied by a rope to the balcony. Horace Van Norman Hilberry (?-1986) stood ready to cut this rope if the automatic rods failed for any reason. Finally, a liquid control squad stood on a platform above the pile trained and ready to flood the whole pile with water containing a cadmium salt in solution.

Fermi started the test at 9:54 am by ordering the control rods withdrawn. Six minutes later Zinn withdrew Zip by hand and tied it to the rail of the balcony. At 10:37 Fermi, still tensely watching the control board, ordered Weil to pull out the vernier control rod thirteen feet. Half an hour passed and the automatic safety rod was withdrawn and set. The clicking in the Geiger counter grew faster and the air more tense. "I'm hungry. Let's go to lunch," said Fermi, and his staff eased off to return to the pile at 2 o'clock in the afternoon. More adjustments, more orders, and at 3:21 Fermi computed the rate of rise of neutron count. Then suddenly, quietly, and visibly pleased, Fermi remarked, "the reaction is self-sustaining. The curve is exponential." Then for 28 more minutes the pile was allowed to operate. At 3:54 P.M. Fermi called "OK" to Zinn, and the rod was pushed into the pile. The counters slowed down. It was over. The job that came close to being a miracle was completed. December 2, 1942 marked the first time in history that men had initiated a successful, self-sustaining nuclear chain reaction. Only a handful of men surrounding Enrico Fermi knew that on this wintry Wednesday afternoon mankind had turned another crucial corner.

The Story of the Atomic Bomb

Control of atomic fission and development of the atomic bomb marked the coming of age of US physics as dominant not just over Europe, but also over chemistry and other sciences. In just a few decades, physics had moved from the discovery of subatomic particles to unlocking vast power from that discovery and from a cascade of scientific discoveries that ensued. As much as the 20th Century was the American Century, it was also the Physics Century, and America’s scientific and technological strength continuing to depend on our strength and discoveries in physics.

Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.