Implications of fission mass distributions for the astrophysical r-process

Abstract

The role of nuclear fission in the astrophysical r-process is examined, and calculated fission fragment mass distributions are utilized to interpret observed elemental abundance data. A number of features of the solar system abundance curve are accounted for. An extension of the r-process to neutron numbers near 200 is required to provide a fission-source explanation of the rare-earth abundance peak. An r-process path that crosses the 184-neutron shell at A=276 (about 4 Z-units lower than presently accepted) is suggested to account for the rare-earth abundances and the high ratio of masses 136 to 148. The ''xenon anomaly'' is discussed within the general context of the treatment, and a superheavy fission precursor is shown to be unlikely. Correlations of abundance anomalies in Ap stars are pointed out, and the anomalies are classified according to cycle time.