The work of Henri Becquerel and the Curies (Pierre and Marie) introduced the new phenomenon of radioactivity to the scientific community. The first two decades of the twentieth century were a true golden age of intellectual achievement. Max Planck introduced quantum theory in 1900 and Albert Einstein special relativity in 1905. Their work constituted the two foundational pillars of all modern physics and profoundly influenced the trajectory of our global civilization. Ernest Rutherford proposed the concept of the atomic nucleus and Niels Bohr refined this nuclear atom model by combining atomic theory with quantum mechanics. Also during this seminal period, Frederick Soddy collaborated with Rutherford in proposing the law of radioactive decay and then went on to propose the existence of isotopes. Victor Hess used a number of daring balloon flights to discover the highly energetic cosmic rays that bombard Earth from outer space.
The 1920s proved equally exciting for nuclear scientists. Arthur Holly Compton performed a watershed X-ray scattering experiment that placed all of quantum mechanics on a sound experimental basis. Many other capable scientists contributed to a rapidly evolving quantum model of the atom. Experimental physicists like Charles Wilson, Sir John Cockcroft, Ernest Walton, and Ernest O. Lawrence introduced pioneering instruments and machines that allowed other scientists to more precisely explore the exciting world of subatomic physics.
In 1932, Sir James Chadwick discovered the neutron. His discovery led the way the to the discovery of nuclear fission by Otto Hahn in 1938 and to the world’s first nuclear reactor, constructed by Enrico Fermi in 1942. Political turmoil in Europe produced many refugee scientists, such as Lise Meitner, who played important roles in the quest to understand and harness the energy locked within the atomic nucleus.
During the 1930s and 1940s, scientists discovered important new isotopes, such as deuterium, discovered by Harold Urey. Working at the Lawrence Radiation Laboratory in Berkeley, scientists began synthesizing a family of transuranic elements, including plutonium—the fissile nuclide first identified by Glenn T. Seaborg and his associates at the laboratory in February 1941. These new materials exerted a tremendous influence on the application of nuclear technology.
Following World War II, in response to the U.S. atomic bomb monopoly, Andrei Sakharov spearheaded the rapid development of the Soviet hydrogen bomb (1953). His successful efforts accelerated a world-endangering nuclear arms race. However, Sakharov also became a force for great social change in the Soviet Union. As a man of both conscience and great personal courage living in a strict totalitarian political environment, he vigorously campaigned for an end to the atmospheric testing of nuclear weapons by the Soviet Union. Reception of the Nobel Prize for peace formally anointed this Russian nuclear physicist as the global champion for human rights of politically oppressed peoples everywhere.
While the dominant emphasis of nuclear research in the 1940s and 1950s was weapons related, scientists also began using nuclear technology to study the past and to understand the vast heavens beyond the boundaries of Earth. Hans Bethe presented the thermonuclear reactions that helped explain the enormous energy output of the Sun and other stars. When Willard Frank Libby introduced the concept of radiocarbon dating in 1947, he gave archaeologists, anthropologists, earth scientists, and historians an exciting new technique with which to accurately study the past. In the early 1960s, Bruno Rossi pioneered X-ray astronomy and provided an entirely new way for scientists to observe the universe.
Luis Alvarez was a multitalented experimental physicist whose numerous contributions to science range from the U.S. atomic bomb project during World War II to a far-reaching extraterrestrial catastrophe hypothesis he copresented with his son (Walter Alvarez) in the early 1980s. Of special significance here is the fact that after World War II Alvarez developed the liquid-hydrogen bubble chamber, in which numerous subatomic particles and their intriguing reactions could be accurately detected. His pioneering work helped promote the “nuclear particle zoo” era—an exciting time of discovery in nuclear physics that continues to the present day..