Enrico Fermi – The Manhattan Project
Enrico Fermi was the most complete physicist of the past century – the world’s theoretician and first-class experimenter. No other physicist after Fermi was so easily balanced between theory and experiment and it is unlikely that such a thing will ever be found. The field of research was too wide to make such jumps possible.
Fermi was born September 29, 1901 in Rome, as the third child of Alberto Fermi, a civil servant, and Ida De Gatis, a teacher. He exhibited a remarkable talent for mathematics and physics as a student at the Pisa High School.
His first major contribution to physics was the analysis of the behavior of certain fundamental particles that make up the matter. (These particles – protons, neutrons, and electrons – are now called fermions in his honor.) Fermi has shown that when composing matter identical fermions come in close contact with each other, which is why the reflective forces that prevent further compaction grow. This fermionic reflection is important for our understanding of such different phenomena as the thermal conductivity of metals and the stability of “white dwarfs”.
Fermi’s theory of beta-decay (the type of radioactivity with which the massive core emits electrons) definitely drew its international reputation. According to this theory, each electron had to be emitted and the avetine particle he called neutrino – “neutral malish”. Not all were convinced of the existence of this hypothetical fermion, but it turned out that Fermi was right. In 1956, physicists experimentally established the existence of neutrino. Although neutrino, because of its reluctance to react with normal matter, retained the attribute “avetinjski”, its properties strongly influenced modern astronomical and cosmological theories.
Receiving the Nobel Prize
In 1938, Fermi received the Nobel Prize in Physics. The award was granted in part for the original nuclear sounding technique. This technique led to the discovery of new radioactive elements; bombarding natural elements with neutrons, he created more than 40 artificial radioisotopes. His award, among other things, was also assigned to the method of slowing down the neutron. Although this seems to be a less important discovery, it has exceptional practical applications because slow neutrons are much more effective in induction of radioactivity than fast ones. (Slow neutron spends longer in the neighborhood of the target core, and it is more likely to react with it. In a similar way, it is more likely that a well-targeted golf ball will fall into the hole if it moves slowly: a quick ball can obstruct the hole .) This principle is used in the operation of nuclear reactors.
The news of the award was almost overshadowed by the rapid deterioration of the political situation in Italy. Under the increasingly powerful influence of Hitler, Mussolini began an anti-Semitic campaign. The Italian fascist government passed laws that were a bit of a copy of the Nuremberg Nazi edicts. Laws did not directly threaten Fermi and his two children who were considered to be Aryans, but Fermi’s wife Laura was a Jew. Together they decided to leave Italy and Fermi accepted the appointment in America.
The Manhattan Project
Two weeks after arriving in New York, Fermi received news that German and Austrian scientists experimented with nuclear fission experimentally. Einstein decided to write his own historical letter to Roosevelt, pointing to the possible consequences of nuclear fission. Stating the work of Fermi and his associates, Einstein warned of the possibility of causing a chain reaction in a large uranium mass – a reaction that could free up enormous amounts of energy. Roosevelt was shy enough to direct funds to a defense research program. Fermi was intensively involved in this program.
Physicists had to answer numerous questions before they were able to build a bomb, and Fermi had solved many of them. On December 2, 1942, an improvised laboratory built on the squash court beneath the western stands of the University Stadium in Chicago, Fermi’s group successfully performed the first self-sustaining nuclear reaction. The reactor (or atomic furnace) consisted of pores of purified uranium – about six tons, all in all – arranged in a graphite matrix. Graphite slowed down the neutrons, allowing them to induce further fission and maintain a chain reaction. The speed of the chain reaction is regulated by cadmium control points (a strong neutron absorber). The reactor entered the critical phase at 2 hours and 20 minutes afternoon, and the first test lasted 28 minutes.
Fermi, as an incomprehensible connoisseur of nuclear physics, significantly contributed to the Manhattan project. On that day, July 15, 1945, Alamogordo joined the nuclear probe Trinity in the desert, lying on the ground fifteen kilometers from the zero point. When the glare of a monstrous explosion passed, he jumped to his feet and dropped a handful of papers in the air. In a calm air, papers would quickly fall to the ground, but when a shock wave came in a few seconds after the flash, they moved parallel to the ground due to air pressure. And, quite typical for him, he used that moment to measure the horizontal shift of papers; since he knew the distance from the center of the explosion, he could immediately assess the energy released from it.
After the war, Fermi returned to academic life at the University of Chicago and was interested in the nature and origin of cosmic rays. In 1954, among other things, he was diagnosed with gastric cancer. Emilio Segre, Fermi’s longtime friend and associate, visited him at the hospital. Fermi rested after an exploratory operation and was attached to the infusion. Even before the end, as Segre tells, Fermi kept his love for observation and calculation: with the stopwatch he measured the infusion rate by counting the drops.
Fermi died on November 29, 1954, in his 53rd year.