Some Late Effects in Mice of Ionizing Radiation from an Experimental Nuclear Detonation

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Abstract
The first experimental investigation of the late effects of ionizing radiations from a nuclear detonation in a very large population of mammals (mice) was planned with great care by a team of investigators of the Atomic Energy Commission and the Armed Forces. The animals were placed at various distances from the hypocenter, and the intensity of exposure was monitored by both physical and biological methods. The mice were of the genetically uniform LAF1 strain, of both sexes, and six to twelve weeks of age when exposed. After the early mortality rates had been recorded, the animals were transported to Oak Ridge, where they remained individually caged, the cages randomized in one large animal room, until natural death. Sick animals were killed in extremis. The radiations from the nuclear detonation were composed predominantly of high-energy gamma rays, with a small component of fast and a still smaller component of slow neutrons, the gammaneutron ratios increasing with the distance from ground zero. The partial preliminary survey now to be reported was made thirty months after the detonation, when most of the exposed animals and about two-thirds of the controls were dead. While the events to be reported are undoubtedly correct, the figures given are subject to minor revision. The total number of mice studied is about 4,000. All dead animals are being preserved and will be made available to those interested in special studies. The gross anatomical findings are being supplemented by microscopic examination whenever necessary. Mortality: The LD50 (30 days) was approximately 755 r in both males and females (Table I). There was some delayed death among the massively irradiated animals during the subsequent few weeks, followed by a period of apparent well-being of the survivors.

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