The waiting point approximation inr-process calculations

Abstract

The steady flow approximation to ther-process has been used to evaluate the validity of the waiting point assumption (that, for a given charge numberZ, neutron captures become balanced by neutron photodisintegrations) under a variety of conditions. The criterion for the accuracy of the approximation for any set of nuclei with the same value ofZ is that the ratio of the total rate of neutron photodisintegration in those nuclei to the total rate of neutron captures should be close to unity. We have failed to find any set of conditions involving neutron production by helium thermonuclear reactions (at temperatures up to 109 K) for which the waiting point approximation is useful for all values ofZ, and we recommend that all suchr-process calculations not use this approximation. At higher temperatures, such as those characteristic of explosive carbon burning (2×109 K), the waiting point approximation is much better.