The Biologic Effects of Pile Radiations

An extensive biological program was undertaken as a part of the Manhattan Project when it was realized that hazardous amounts of high-energy radiations would frequently be encountered during the production of plutonium and the various radioactive isotopes. The studies undertaken were directed toward a determination of biological effects such as might be encountered on the project. The most immediate need for an investigation was the provision of a more adequate experimental basis for the tolerance levels adopted to protect personnel. Although it was considered important to determine the maximum dose of radiation which could be absorbed with impunity, it was also considered important to determine the effects produced under a wide variety of experimental conditions and, if possible, some features of the mechanism whereby these changes occurred. The latter general objective accordingly consisted of the determination of biologic effects resulting from various radiations and various types of exposure; also it included examination of results for clues indicative of the methods of radiobiologic action. Some of the specific objectives were: (1) to determine the nature of late irradiation damage in animals receiving (a) small periodic doses and (b) near lethal doses of fast and slow neutrons, gamma rays, and beta particles; (2) to determine the relative effectiveness of fast and slow neutrons and gamma rays (penetrating radiations); (3) to obtain information on thresholds and tolerance levels in animals receiving the various treatments; (4) to determine species and sex idiosyncrasies; (5) to gather information on the mechanism of radiobiologic action. The findings in investigations directed toward achieving these objectives were expected to be of value to future developments, such as the treatment of radiation injury, cancer therapy, the therapeutic applications of radiations to other ailments, and the use of radioactive substances in biological research. Methods and Materials Radiation Sources: A fast neutron may arbitrarily be described as a neutron “more likely to produce an ionization track by elastic scattering than by being captured,” that is, with energies from 103 ev. to more than 4 Mev. By the same reasoning a slow neutron may be described as one more likely to produce an ionization track by being captured than by elastic scattering, with energies less than 103 ev. The fast and slow neutron studies were made by means of special carts designed to provide space for animals during treatment and facilities for intensifying and purifying the radiation to be used. For reasons of security, a description of these facilities will have to be omitted at this time. The carts, containing the animals, were wheeled into the center of the pile and were thus subjected to the action of a high neutron field.