American Work on the Atomic Bomb Project

Abstract

JUST as soon as it was discovered that secondary neutrons are liberated in uranium fission to the extent of considerably more than one for each heavy nucleus transformed, and that types of nuclei exist which undergo fission under bombardment with neutrons of all energies, it became a reasonable scientific guess that the attainment of a self-propagating (divergent) nuclear chain-reaction would eventually prove possible. So much was, in fact, commonly known by physicists in the late summer of 1939—and the implications of this knowledge in relation to the likely development of military weapons of extreme power were not altogether unheeded by scientific men whose countries were very obviously slipping helplessly into war. In the United States, also, attempts to arouse official interest in the new possibilities were not entirely without effect. By slow degrees this latter interest quickened, and a few weeks before the Japanese attack on Pearl Harbour, American service chiefs were ready to sanction a greatly intensified effort on the problem. Early in 1942 a full-scale research and development programme was under way and plans for pilot production plants were in hand. Almost exactly three years later, what had appeared in sober estimate so distant was an actuality; the first bomb had not been dropped, but the scientific workers in charge of the project were satisfied that success was well-nigh inevitable, and large production plants were rapidly accumulating the fissile material which it was planned to use.