| Roughly half of all nuclei with mass A > 70 and nearly all of the rare earth elements are produced by two process of neutron capture on lighter nuclei. These processes are called the rapid, or r-, process, and the slow, or s-, process, their names indicative of the rate of neutron captures relative to the stabilizing β-decays. The r-process must necessarily exist in an environment of high neutron flux. Therefore, nuclei produced in the r-process, which are the progenitors of the stable nuclei observed today, fall along a locus in the very neutron rich region of the isotopic chart known as the r-process path. Progression along the r-process path occurs through a sequence of neutron captures and β-decays. Since neutron captures are very fast, the r-process is primarily limited by β-decays. The very neutron-rich nuclei along the r-process path are, for the most part, beyond the reach of experimental physics, despite their importance to modern nuclear astrophysics. Of primary importance in an analysis of r-process nucleosynthesis are the β-decay half-lives. An alteration in the half-lives can change the path and pace of the r-process. Difficulties in current r-process predictions include the difficulty of current models to manufacture sufficient nuclei in the mass region A∼200 region. However, the inclusion of excited state β-decays may resolve this difficulty by allowing a population of nuclei along the r-process path to speed up the r-process, so that it can move rapidly to the higher masses. The problem is further complicated by the lack of knowledge of many of the r-process progenitor nuclei; indeed, many have not been studied. The theoretical problem of β-decays of excited state nuclei as well as the production of high mass nuclei via an r-process are both attacked in this work, the results of which are mutually supportive. Future experimentation is discussed as a final note. |
