CHAPTER 1 FIRST HUMAN MADE REACTOR AND BIRTH OF NUCLEAR AGE © M. Ragheb 8/6/2012 “The energy produced by the atom is a very poor kind of thing. Anyone who expects a source of power from the transformation of these atoms is talking moonshine.” Lord Ernest Rutherford, 1933 “The Almighty certainly never intended that people should travel at such breakneck speed.” About trains travelling at 15 miles per hour. Martin van Buren, 1830. 1.1 INTRODUCTION The events that accompanied the birth of the nuclear age are described. The construction of the Chicago Pile Number 1 (CP-1) as the first human made nuclear reactor and the milestones in scientific progress that preceded and immediately followed it are considered. The success of the first man-made self-sustained chain reaction was followed by the Manhattan Project, which culminated into the first and only use of nuclear weapons in warfare by the USA against Japan. The distinction between a nuclear reactor and a nuclear device using an exponential neutron population growth model is discussed. Humanity's hope lies in using its acquired knowledge in constructive endeavors, and refraining from its use for destructive actions. This process still continues in the nuclear age and affects every human in some special way. 1.2 THE CHICAGO PILE NUMBER ONE, CP-1 REACTOR The following coded message was sent from the Stagg Field at the University of Chicago to government officials in Washington DC: “You will be interested to know that the Italian navigator has just landed in the New World, and the natives are friendly.” The Italian navigator referred to was not Christopher Columbus (1451-1506), but Enrico Fermi (1901-1954). “The natives were friendly,” alluded to the success of a major experiment designated as the Chicago Pile Number 1: CP-1. A painting by artist Gary Sheahan that reconstructed the event showing Enrico Fermi's team is shown in Fig. 1.Figure 1. Painting by artist Gary Sheahan reconstructing the Chicago Pile Number 1 experiment: CP-1, first reactor showing Enrico Fermi's team. Enrico Fermi was an experimental and theoretical physicist, born in Rome, Italy in 1901. He taught theoretical physics at the University of Rome in Italy. He was the co-inventor with Leo Szilard of the nuclear pile. He had received a Nobel Prize in Physics for atomic research in 1938: “On the absorption and diffusion of slow neutrons.” He directed the building of the first reactor at the Metallurgical Laboratory at the University of Chicago. Enrico Fermi adhered to the Catholic Christian faith and was married to a Jewish spouse. He escaped the then prevalent nationalistic Fascism and Nazism in Europe to teach at Columbia University in the USA, where he became involved in the field of neutron physics. Humans initiated a self-sustained nuclear chain reaction and controlled it for the first time on December 2, 1942. This occurred beneath the West Stands of Stagg Field, Chicago in the State of Illinois in the USA, at 3:25 in the afternoon. Figure 2. Enrico Fermi (1901-1954).In the center of the 30 by 60 feet squash court, where it was constructed, the reactor consisted of a pile of graphite bricks and wooden timbers. It was square at the bottom and flattened as a sphere near the top. As an extra safety feature, it was shrouded on all but one side by a gray balloon cloth envelope, provided by the Goodyear rubber company, to contain any unexpected radioactivity release. Its sides were straight up to half its height, and the top was domed like a beehive. The squash court was situated under the ivy covered stands of the University of Chicago's Stagg Field, named after baseball's Grand Old Man: Amos Alonzo Stagg. This experiment was part of an effort that started a few months earlier aimed at releasing energy from the nuclear fission process. The project was given the code name: “Manhattan District Project,” in short: “The Manhattan Project.” The objective was to build an explosive fission device. However, the scientists here were at the preliminary stage of investigating whether a self-sustained release of fission energy could be achieved in the first place. Starting in April 1942, two test piles were built at the Stagg field in Chicago. By November 1942, Fermi and his coworkers had constructed a lattice of carbon blocks in the form of a graphite cube, containing lumps of uranium in the form of spheres. The uranium was the fuel for the reaction while carbon, in the form of ultra-pure machined graphite, slowed down the neutrons originating from the fission process in the uranium fuel through collisions with the graphite nuclei from their average fission energy of about 2 Million electron Volts (MeV) down to the thermal equilibrium energy with the surrounding medium of 0.025 eV. This is a factor of: 662 1080 100.025×= × or an 80 million times reduction in energy. It was then known that the nuclear fission process is more likely to occur in the rare U235 isotope, not the more abundant U238 isotope of uranium. In addition, the probability of fission of the isotope U235, or its nuclear cross section, is enhanced if the neutrons are slowed down from their fast 2 MeV kinetic energy to the slow 0.025 eV thermal equilibrium energy. This is contradictory to classical physics where a large amount of kinetic energy would be more capable of splitting the uranium nucleus. However, at these energies, the neutrons behave more like waves than particles. Under this circumstance, their wave behavior is best described by Quantum Mechanics, rather than by Classical Mechanics. A simple heuristic model envisions the uranium nucleus as a potential well into which a sluggish slow neutron can drop and be readily absorbed as a wave, distributing its energy among the nucleons in the nucleus and causing it to fission. Conversely, a fast neutron as a wave would readily pass over the well, jumping over it without falling in and be captured by it.Figure 3. Photograph of the layering of the graphite blocks containing the lumped uranium spheres at the level of the tenth layer, 1942. Graphite block from CP-1, Photo courtesy: Paul Mikols. It was also known that to use natural uranium for a chain reaction necessitates the use of a moderator material, which does not appreciably absorb the neutrons. From that perspective, carbon as graphite, beryllium or heavy water (HDO or D2O)