The Plutonium Project

Abstract

THE Plutonium Project was assigned the task of making and purifying the artificial element plutonium for use in atomic bombs. The method of making plutonium utilized the nuclear reaction between neutrons and uranium238, the neutrons being excess from a so-called nuclear chain reaction maintained by other neutrons and uranium235. The uranium238 and uranium235 were not separated. They were in their natural mixed condition. The fact that the chain reaction was used meant that according to pre-war standards fantastic amounts of gamma rays and fast and slow neutrons would be emitted in a chain reactor of any considerable magnitude. We were familiar, to a certain extent, with these radiations before the war, but we had had no experience whatever with the large amounts anticipated in a chain reactor. In addition to the tremendous potential hazards due to the radiations emitted in the chain reaction, there were also enormous hazards to be anticipated in the purification of the plutonium, since plutonium was formed in masses of uranium and had to be separated from that element. Moreover, included in this mixture was a large variety of so-called fission products formed in the fission of uranium235 after its absorption of a neutron. These fission products are highly diverse in their chemical natures and in the types and energies of the radiations which they emit. They are all radioactive. Consequently, it was rightly anticipated that, unless stringent control measures were set up, it would be very easy for personnel to take into the body, by ingestion, inhalation, or through wounds, certain of these fission products, to say nothing of plutonium itself, which is also radioactive. It was early recognized in the Project not only that control measures must be set up but that it might be an excellent idea to carry out extensive and, so far as possible, intensive radiobiological research with a view to learning how hazardous the various radiations are, to what degree the dangerous radioactive substances may be taken into the body by various routes, how long they stay in the body, where they stay while there, and how dangerous any definite amount thus retained may be. The radiobiological work of the Plutonium Project was carried out at various sites. During the war all of these sites were under the direction of one of your colleagues whom you know well—Dr. Robert S. Stone. The sites where most of the research was carried out were the University of California; the Metallurgical Laboratory of the University of Chicago, which is now the Argonne National Laboratory; Clinton Laboratories near Oak Ridge, Tennessee; and the National Cancer Institute. I might also point out that the Plutonium Project was only one part of the gigantic Manhattan District and that other radiobiological work was carried on in the District aside from that in the Plutonium Project, the most active sites being at the University of Rochester and at Columbia University.