Atoms and More: Physics

ATOMS AND MORE: PHYSICS

The Physical World

Physics arguably got one of its great boosts in the 1930s thanks to work in the United States and Europe. However, the flow of scientists fleeing European dictatorships for the United States also contributed substantially to progress in America. Cosmic rays constituted a subject of interest in astrophysics, as Carl David Anderson in 1932 confirmed the existence of the antielectron, or positron, whose existence the British physicist P. A. M. Dirac had predicted. Pursuing research together with Seth Neddermayer, Anderson discovered the existence of another particle in 1937, which he first called a meson; its mass was greater than that of the electron but smaller than that of the proton. This discovery caused several problems in the establishment of experimental conditions in a particle accelerator; since the direction of these particles' energy could not be predicted, detectors might not react with the expected accuracy. Eventually the presumed meson failed to react as predicted by other scientists, and its name was changed to muon because of its differing characteristics.

New Aspects of the Atom

The Berkeley Laboratory in California, under the leadership of Ernest O. Lawrence, attracted many scientists interested in working with the first cyclotron, a particle accelerator invented by Lawrence and built by Niels Edlefsen and the ancestor of the huge circular accelerators of the post—World War II era. In 1932 James Chadwick of England discovered the neutron, which forms the basis of nuclear fission. In 1934 Frederic Joliot-Curie and Irene Joliot-Curie announced the first case of artificially produced radioactivity. Two years later Hungarian-born American physicist Eugene Paul Wigner established the mathematics that ruled the way in which neutrons were absorbed by an atom's nucleus and how the mathematics varied according to the neutron's energy. Thus, the neutron became the particle of choice in bombarding elements to obtain isotopes. Specialists in the field included Enrico Fermi and Emilio Segre, both of whom would later work in the United States. In 1938 this line of work gained in importance with the discovery in Germany and Sweden by Otto Hahn, Lise Meitner, and Fritz Strassmann that bombarding a uranium isotope could result in liberating enormous amounts of energy. In New York in 1939 Danish physicist Niels Bohr described this process of fission at a meeting of the American Physical Society.

Working toward the Bomb

By that time scientists working in the United States were especially concerned with drawing the interest of the American government to the potential of atomic science, fearing that other nations might gain an advantage. Fermi, Leo Szilard, and several other physicists took steps first to interest the American military in 1938, then to draw President Franklin D. Roosevelt's attention. Szilard convinced the openly pacifist Albert Einstein to write the president on 2 August 1939 to request that an atomic bomb be built before Nazi Germany could develop one.

Sources:

J. L. Heilbron and Robert W. Seidel, Lawrence and His Laboratory (Berkeley: University of California Press, 1989);

Richard Rhodes, The Making of the Atomic Bomb (New York: Simon & Schuster, 1986).