Half-lives and branchings for {\beta}-delayed neutron emission for neutron-rich Co-Cu isotopes in the r-process

TL;DR

This study provides new experimental measurements of beta-delayed neutron emission probabilities and half-lives for neutron-rich Co-Cu isotopes, improving r-process nucleosynthesis models and understanding of astrophysical element formation.

Contribution

First-time measurements of Pn values for 74Co and 75-77Ni, and new half-life data for 75Co and 80Cu, enhancing r-process modeling accuracy.

Findings

New Pn values for 74Co, 75-77Ni, 77-79Cu, 81Zn, 82Ga.

First half-life measurements for 75Co and 80Cu.

Improved agreement of classical r-process models with solar abundance patterns.

Abstract

The {\beta} decays of very neutron-rich nuclides in the Co-Zn region were studied experimentally at the National Superconducting Cyclotron Laboratory using the NSCL {\beta}-counting station in conjunction with the neutron detector NERO. We measured the branchings for {\beta}-delayed neutron emission (Pn values) for 74Co (18 +/- 15%) and 75-77Ni (10 +/- 2.8%, 14 +/- 3.6%, and 30 +/- 24%, respectively) for the first time, and remeasured the Pn values of 77-79Cu, 79,81Zn, and 82Ga. For 77-79Cu and for 81Zn we obtain significantly larger Pn values compared to previous work. While the new half-lives for the Ni isotopes from this experiment had been reported before, we present here in addition the first half-life measurements of 75Co (30 +/- 11 ms) and 80Cu (170+110 -50 ms). Our results are compared with theoretical predictions, and their impact on various types of models for the astrophysical rapid neutron-capture process (r-process) is explored. We find that with our new data, the classical r-process model is better able to reproduce the A = 78-80 abundance pattern inferred from the solar abundances. The new data also influence r-process models based on the neutrino-driven high-entropy winds in core collapse supernovae.