The present status of scientific applications of nuclear explosions

This is the fourth in a series of symposia which started, in 1957 at Livermore with the purpose of examining the peaceful uses of nuclear explosives. Although principal emphasis has been placed on technological applications, the discussions have, from the outset, included the fascinating question of scientific uses. Of the possible scientific applications which were mentioned at the 1957 meeting, the proposals which attracted most attention involved uses of nuclear explosions for research in seismology. It is interesting to note that since then a very large and stimulating body of data in the field of seismology has been collected from nuclear tests. Ideas for scientific applications of nuclear explosions go back considerably further than 1957. During the war days Otto Frisch at Los Alamos suggested that a fission bomb would provide an excellent source of fast neutrons which could be led down a vacuum pipe and used for experiments in a relatively unscattered state. This idea, reinvented, modified, and elaborated upon in the ensuing twenty-five years, provides the basis for much of the research discussed in this morning's program. In 1952 a somewhat different property of nuclear explosions, their ability to produce intense neutron exposures on internal targets and to synthesize large quantities of multiple neutron capture products, was dramatically brought to our attention by analysis of debris from the first large thermonuclear explosion (Mike) in which the elements einsteinium and fermiun were observed for the first time. The reports of the next two Plowshare symposia in 1959 and 1964 help record the fascinating development of the scientific uses of neutrons in nuclear explosions. Starting with two 'wheel' experiments in 1958 to measure symmetry of fission in 235-U resonances, the use of external beams of energy-resolved neutrons was expanded on the 'Gnome' experiment in 1961 to include the measurement of neutron capture excitation functions for 238-U, 232-Th, 197-Au, and 180-Hf by M. Lindner at Livennore. The list of experiments grew longer in 1964 with the addition of several fission cross-section measurements, marking the beginning of the physics cross-section measurement program at Los Alamos. Since then four more nuclear tests with energy-resolved neutron beams have been used for physics and nuclear chemistry experiments, one each in 1965, 1967, 1968, and 1969. The major developments during this period include successive large numbers of measurements on each new test, a steady improvement in the ability to prepare and measure the neutron cross sections of very small samples and very radioactive samples, an expansion in the capacity to record and analyze enormous numbers of data points, and a better understanding of the techniques for shaping neutron spectrum to best satisfy the varying demands of a large number of experiments. By 1969 the number of experiments on a single test had grown to thirty-two