From Nuclear Transmutation to Nuclear Fission, 1932–1939 , Per F. Dahl IOP, Philadelphia, 2002. $75.00 (304 pp.). ISBN 0-7503-0865-6
Nuclear physics started with radioactivity. At first, no way could be found to alter radioactive decay rates: Nuclear transmutations occurred at their own inexorable pace. Then, in 1919, Ernest Rutherford showed that alpha particles from natural radioactive decay that pass through nitrogen could generate hydrogen nuclei. That was the first observation of an externally-induced nuclear transmutation. Ten years of further study led to some extension of the initial results, but also stimulated a strong desire for beams of artificially accelerated particles that could be more intense and more under the experimenters’ control.
In 1928, George Gamow, and independently Edward Condon and Ronald Gurney, explained quantum-mechanical barrier penetration. Their explanations helped physicists understand how charged particles get out of a nucleus in radioactive decay—and further, how such particles might tunnel into the nucleus. Thus began what Per F. Dahl calls, in the preface to his book From Nuclear Transmutation to Nuclear Fission, 1932–1939, “… a race, circa 1930, between four laboratory teams to be the first to achieve the transmutation of atomic nuclei with artificially accelerated nuclear projectiles.” Dahl’s title is a bit of a misnomer; much of the book concerns what happened before 1932.
Dahl follows closely the work of the research groups led by John Cockcroft at the Cavendish Laboratory in Cambridge, England; Merle Tuve at the Carnegie Institution of Washington, DC; Ernest Lawrence at the University of California, Berkeley; and Charles Lauritsen at Caltech. Cockcroft and Ernest Walton won the race in April 1932, when they saw the alphas generated by 600-keV protons on lithium, but the other labs were not far behind, and each made impressive contributions in the next few years. Dahl’s story is based in part on archives at the University of California, Berkeley; in Cambridge at Churchill College, the Cambridge University Library, and the Cavendish Laboratory; at the Center for History of Physics in College Park, Maryland; and at the Library of Congress and the Carnegie Institution, both in Washington, DC. The story is rich in the interplay among physicists in the context of economic depression and the rise of fascism. Anyone with even a moderate interest in how physics developed in the 1920s and 1930s will enjoy the book.
Dahl amply documents an exciting time for physics. Consider just the first half of 1932. January saw the report by Harold Urey, Ferdinand Brickwedde, and George Murphy of the discovery of deuterium. February brought James Chadwick’s discovery of the neutron and a crucial advance in cyclotron operation at Berkeley. In April came the Cockcroft—Walton work, and June saw Carl Anderson’s discovery of the positron and Werner Heisenberg’s description of the nucleus in terms of protons and neutrons as isospin partners (in all but name).
The Cavendish lab won the race for artificial disintegration, but four years later Tuve, Gregory Breit, Lawrence Hafstad, and Norman Heydenburg at the Carnegie Institution made the first direct studies of the nucleon—nucleon interaction. Much information about the interaction had been inferred from data on nuclear masses and sizes, as one can see from the review by Hans Bethe and Robert Bacher (Rev. Mod. Phys. 8, 82, 1936). But if one wants to learn about an interaction, nothing is more fundamental than a scattering cross section. Scattering of all sorts—elastic, inelastic, and transmutational—would become the preeminent tool in nuclear and particle physics.
Dahl concludes his history with an original and exciting account of the early developments in nuclear fission—a special kind of transmutation in which one element becomes two. The discovery of fission in 1938–39 was a major paradigm jolt, which led to an eruption of activity among physicists and chemists that culminated in the Manhattan Project.
The raisins in this plum pudding of a book include accounts of the lifelong friendship and occasional rivalry between Tuve and Lawrence, the difficulties faced by Tuve and his group in trying to achieve high DC voltage by using a Tesla coil, the development by Robert J. Van de Graaff of his moving insulator-belt generator of high voltages, the work of Lawrence and Stanley Livingston on the cyclotron, and the work of Lauritsen in developing high-voltage x-ray generators for medical use and then adapting them to nuclear physics.
An especially interesting theme brought out by Dahl is the importance of Norwegians and other Scandinavians in the development of accelerators and early nuclear physics. Tuve and Lawrence were of Norwegian descent, Hafstad was the son of a Norwegian immigrant, and Norwegian engineer Rolf Wideröe had conceived the basic ideas of several methods of particle acceleration. The Swedish physicist Gustaf Ising thought up the traveling-wave linear accelerator in Stockholm. Lauritsen was Danish. Even more intriguing is the extraordinary career of the Norwegian Odd Dahl—aviator, explorer, pioneer in radio wave propagation, oceanographer, designer and builder of particle accelerators, and father of the book’s author, to mention only a few highlights.
Per Dahl is now retired from the Lawrence Berkeley National Laboratory, where he made important contributions to the development of super-conducting accelerator magnets. On the history of physics, he published four previous books, which covered conservation of energy, superconductivity, the discovery of the electron, and the story of Norwegian heavy water and its role in World War II.
It is not easy to weave as much as Dahl has into a coherent whole, especially when many of the side stories are as interesting as the main scientific thread. Dahl has effectively organized his work so that the main and tangential stories come through clearly. The history is well worth revisiting and Dahl’s summary of it is fresh and engaging.
