До фисије, о фисији и о уранијуму

Abstract

This book describes the scientific phenomenon of nuclear fission and the research that led to its discovery. Our intention was to familiarize the broad public with the concept and the discovery of fission. Nuclear fission was one of the key discoveries in the history of science, and was quickly applied practically, both in a constructive and in a destructive fashion. This book is also an expression of our desire to emphasize that science and scientific method are indispensable in societies that seek to develop and better themselves. Fission is a nuclear reaction in which an atomic nucleus is broken apart into two smaller nuclei by neutron impact, with the release of vast amounts of energy. It was discovered in 1939 by the German scientist Otto Hahn, who received a Nobel Prize in 1944 for “the discovery of fission of heavy nuclei”. The discovery was preceded by years of research in three research groups that concurrently studied nuclear reactions of neutrons with uranium. In Italy, this research was led by Enrico Fermi. The Berlin team was supervised by Hahn. Finally, the Paris group was led by Irène Joliot-Curie, and included Pavle Savić who collaborated with Joliot-Curie as an assistant. The first part of this book includes a historic introduction and annotated translations of seven key scientific articles that led to the discovery of fission, as well as Otto Hahn’s Nobel lecture. In this lecture, Hahn noted that “fission was a phenomenon defying all other phenomena previously observed in nuclear physics;” this led scientists to be unusually cautious in the interpretation of their own experiments, even when they unambiguously suggested that nuclei were being broken up. This section continues with the article written by the US Nobel Laureate Glenn Seaborg, in which he described how the discovery of fission inspired his own experiments that created transuranium elements. One of the key messages in this section of our book is that fission was discovered accidentally while scientists searched for something else: methods to prepare transuranium (that is, heavier than uranium) elements. These searches were enabled by the 1932 discovery of neutron – an unusual particle without charge, that can easily incorporate itself into an atomic nucleus. The nucleus then becomes heavier and typically turns beta-radioactive; after emitting radiation, it turns into a nucleus of a different chemical element. Uranium nucleus and a neutron – these are the key players in the process of fission. Uranium was also the central element in the discovery of radioactivity in 1896, which is viewed as the beginning of the nuclear era. Today, uranium is a key resource in nuclear energy production, and is expected to maintain that role for several millennia. Uranium is thus a very special element, and the title of our book reflects that. The second part of the book contains the description and interpretation of neutron-induced nuclear fission of uranium, description of fission chain reaction, as well as a chapter dedicated to uranium as a chemical element. We analyze the contribution of uranium to the naturally occurring radioactivity on Earth, as well as its importance in the future of energy technologies. In parallel, we survey the applications of fission in today’s society, with a particular focus on its utilization in energy production. Nuclear fuels are an incredibly dense source of energy, releasing vast amounts of energy per unit of mass; in the case of uranium, these amounts are about ten million times greater than those released in chemical combustion processes. We go on to describe a nuclear reactor – the device that enables controlled harvesting of nuclear energy by keeping the fission in a self-sustaining chain reaction state. We also used this opportunity to introduce the reader to the Oklo phenomenon: the existence of a naturally fueled nuclear reactor billions of years ago. On the other hand, the high concentration of energy in fission has led to its unfortunate applications – shortly after its discovery – in nuclear weapons. Nuclear (or atomic) fission bomb was, at the time, the most terrifying weapon ever used; we describe its basic principle of operation in the section on nuclear weapons. The third part of the book contains appendices that include a glossary of important terms used in the preceding parts of the book, as well as a gallery of photographs of scientists that contributed to the discovery of nuclear fission. Finally, this book speaks about the unique set of conditions under which many scientists worked in the first half of the 20th century. Some of their fates were forever altered by conditions in the buildup to World War II. For example, Lisе Meitner was Otto Hahn’s main collaborator in the discovery of fission, but had to leave Germany because of her Jewish origins. In Italy, Enrico Fermi felt similar pressures and finally emigrated to the US. The development of nuclear fission technology was not free from political pressures in the US either, where the first atomic bomb was developed. One thing is certain: all of them together laid the groundwork for a number of technical and scientific revolutionary discoveries that followed World War II, especially in the domain of nuclear energy and space exploration. Such knowledge-based revolutions continue – although their focus today has perhaps shifted onto other scientific areas.