Nuclear Fission, 1938–1942

For information on American research and development on fission after January 1942, see the page for the Manhattan Project and predecessor organizations.

Contents

Background
Resources
Early Fission Research
Isotope Separation
Chain Reaction Research
Plutonium Research
The Organization of Fission Research and World Events

Background

When nuclear fission was discovered near the end of 1938, it was a totally unanticipated phenomenon. It had been known for decades that an enormous energy was bound up in the atomic nucleus, but there were no clear paths toward gaining experimental, let alone practical, access to that energy. However, the nucleus had already been under intense study throughout the 1930s, as physicists and chemists catalogued the various radioactive elements and their behaviors, came to understand the sources of stability of the nuclei of various isotopes, and transmuted elements by bomarbing them with the newly-discovered neutron and with alpha particles (helium nuclei). Once the initial discovery had been made, the basic outline of the fission process was quickly established, and it did not take long to develop a substantial body of experimental measurement and theory surrounding it.

As an astonishing new development in the physics of the nucleus, fission garned widespread attention, which was further augmented by the implication that fission might be exploited to design new weapons and new sources of power. However, the unprecedented application-oriented research program that developed a few years later can only be understood by taking into account the political context: the 1933 rise to power of Adolf Hitler and his Nazi Party in Germany, and the consequent rise of German militarism and anti-Semitic persecution. Much of the research would be done by scientists who had fled fascist Europe, and the funding, institutional support, and access to personnel that made that research possible was only acquired out of the fear that the Nazis might develop their own fission-based weapon.

All early research in fission took place in independently-directed, penuriously-funded research programs at universities and research institutes. Through the initiative of small groups of scientists, this research was gradually integrated into coordinated state research, development, and industrial production mechanisms, which were themselves gradually growing in size and sophistication in anticipation of the coming war. This topic guide covers the early period of fission research, when application still appeared doubtful or distant to many. It ends semi-arbitrarily with the consolidation of slow-neutron chain reaction research at the University of Chicago in January 1942. Some research, notably work on isotope separation at Columbia University, continued uninterrupted through this time.

Resources

The most complete information on early nuclear fission research can be found in the thorough journalistic account, Richard Rhodes, The Making of the Atomic Bomb (New York: Simon & Schuster, 1986). In anticipation of later events, Rhodes' book sometimes takes a jaundiced view of the pace of support for fission research, and concentrates heavily on some actors while neglecting others.

Rhodes' work can be supplemented with the official history, Richard G. Hewlett and Oscar E. Anderson, Jr., A History of the United States Atomic Energy Commission, Volume I: The New World, 1939/1946 (University Park, PA: Pennsylvania State University Press, 1962). On the British project, see its official history, Margaret Gowing, Britain and Atomic Energy, 1939-1945 (London: Macmillan & Co Ltd., 1964). On early fission research in France, see Spencer R. Weart, Scientists in Power (Cambridge, Mass.: Harvard University Press, 1979).

Another detailed timeline and other reference sources are available through the Atomic Heritage Foundation website.

Early Fission Research

Isotope Separation

Following Niels Bohr's February 1939 explanation of uranium-235 being responsible for the slow-neutron fission in natural uranium, it became important to develop a means of separating the uranium isotopes, which were chemically identical and only incrementally different in mass. This research was motivated by three problems. First, to confirm Bohr's theory, it would be necessary to experiment with uranium samples of differing isotope composition. Second, for any chain reaction to proceed, it was thought it might be necessary to reduce substantially the amount of the less-fissile U238 in the uranium used. Finally, even as it became increasingly clear that slow-neutron chain reactions were possible, it was equally evident that an explosive slow-neutron reaction in natural or U235-enriched uranium would be highly inefficient (i.e., producing only a small explosion) and that the size of the explosive would be prohibitively massive: to build a nuclear explosive, it would be necessary to isolate pure U235 in quantity.

Beginning in the summer of 1940 and moving into 1941 a number of isotope-separation research programs begin work in the United States. These include:


Chain Reaction Research

In late 1940 and 1941 theoretical and experimental research on chain reactions proceeded at a number of locations, with the objects of ascertaining fundamental constants such as neutron-capture and fission cross sections of uranium and other materials, and developing designs for workable reactors. Programs included:


Plutonium Research

The discovery of plutonium, which fissions as easily as uranium-235, provided additional impetus to chain reaction research because it provided a new path to the atomic bomb that did not require difficult and expensive isotope separation methods. Plutonium could be produced in a slow-neutron chain reaction in uranium containing its naturally large concentrations of uranium-238, and then chemically separated into its pure, potentially explosive form.

The Organization of Fission Research and World Events

Home >> Browse >> Topics >> Nuclear Fission, 1938–1942