Largescale evaluation of β decay rates of r process nuclei with the inclusion of firstforbidden transitions
Abstract
Background: r process nucleosynthesis models rely, by necessity, on nuclear structure models for input. Particularly important are β decay halflives of neutronrich nuclei. At present only a single systematic calculation exists that provides values for all relevant nuclei making it difficult to test the sensitivity of nucleosynthesis models to this input. Additionally, even though there are indications that their contribution may be significant, the impact of firstforbidden transitions on decay rates has not been systematically studied within a consistent model.
Purpose: Our goal is to provide a table of β decay halflives and β delayed neutron emission probabilities, including firstforbidden transitions, calculated within a fully selfconsistent microscopic theoretical framework. The results are used in an r process nucleosynthesis calculation to asses the sensitivity of heavy element nucleosynthesis to weak interaction reaction rates.
Method: We use a fully selfconsistent covariant density functional theory (CDFT) framework. The ground state of all nuclei is calculated with the relativistic HartreeBogoliubov (RHB) model, and excited states are obtained within the protonneutron relativistic quasiparticle random phase approximation (p n RQRPA).
Results: The β decay halflives, β delayed neutron emission probabilities, and the average number of emitted neutrons have been calculated for 5409 nuclei in the neutronrich region of the nuclear chart. We observe a significant contribution of the firstforbidden transitions to the total decay rate in nuclei far from the valley of stability. The experimental halflives are in general well reproduced for eveneven, oddA , and oddodd nuclei, in particular for shortlived nuclei. The resulting data table is included with the article as Supplemental Material.
Conclusions: In certain regions of the nuclear chart, firstforbidden transitions constitute a large fraction of the total decay rate and must be taken into account consistently in modern evaluations of halflives. Both the β decay halflives and β delayed neutron emission probabilities have a noticeable impact on the results of heavy element nucleosynthesis models.
 Publication:

Physical Review C
 Pub Date:
 February 2016
 DOI:
 10.1103/PhysRevC.93.025805
 arXiv:
 arXiv:1507.07442
 Bibcode:
 2016PhRvC..93b5805M
 Keywords:

 Nuclear Theory;
 Astrophysics  High Energy Astrophysical Phenomena;
 Nuclear Experiment
 EPrint:
 18 pages, 17 figures, submitted to Physical Review C