Beta Decay of Neutron-Rich Transuranic Nuclei

Abstract

The intense neutron flux generated in a thermonuclear explosion is of interest to nuclear physicists because, among other reasons, the atoms exposed to this flux will undergo many successive capture reactions during the brief period the flux exists. If 238U target atoms are given such exposure, the phenomenon becomes a way to probe the nuclear properties of very neutron-rich uranium nuclei and to produce heavy isotopes of the transuranium elements that survive the chains of beta decay following the initial phase of the reaction. This unique method of transuranium element production was investigated by U.S. scientists in a series of thermonuclear explosions during the period 1952–1969, first as an unexpected result of the Mike explosion [1] that occurred in November 1952 and later in a series of underground explosions where the explosive devices were designed specifically for this purpose [2,3]. The heaviest species identified in this work was 257Fm, which implies the production of 257U during the capture phase. While nuclei this neutron-rich cannot be produced by any other man-made technique, it is known, of course, that such nuclei are generated by the astrophysical r process. The neutron-capture path for this process is thought to pass through a region around 262U[4]. Given the clear relationship between these processes, it is the purpose of this paper to see what insights into recent r-process calculations can be gained from a consideration of the experimental data for heavy element production in thermonuclear explosions.

Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.