Abstract
We investigated the effects of first-forbidden transitions in $\beta$ decays on the production of the r-process $A \sim 195$ peak. The theoretical calculated $\beta$-decay rates with $\beta$-delayed neutron emission were examined using several astrophysical conditions. As the first-borbidden decay is dominant in $N \sim 126$ neutron-rich nuclei, their inclusion shortens $\beta$-decay lifetimes and shifts the abundance peak towards higher masses. Additionally, the inclusion of the $\beta$-delayed neutron emission results in a wider abundance peak, and smoothens the mass distribution by removing the odd-even mass staggering. The effects are commonly seen in the results of all adopted astrophysical models. Nevertheless there are quantitative differences, indicating that remaining uncertainty in the determination of half-lives for $N=126$ nuclei is still significant in order to determine the production of the r-process peak.
Highlights
The rapid neutron-capture process (r process) is one of the major nucleosynthesis processes [1,2], producing nuclei heavier than iron, which include rare-earth elements and actinides
We focus on the impacts of the FF β decay and the β-delayed neutron emission on the production of the A ∼ 195 r-process peak in several astrophysical models
We studied the role of first-forbidden β decay and that of the β-delayed neutron emission on the r process, the effect on the A ∼ 195 peak
Summary
The rapid neutron-capture process (r process) is one of the major nucleosynthesis processes [1,2], producing nuclei heavier than iron, which include rare-earth elements and actinides. Several calculations take into account first-forbidden β decays by the extended quasiparticle random phase approximation (QRPA) [18,19,20,21,22] and shell model approaches [23,24] These studies found a significant contribution, in the range of 20–80%, of the FF transition to the β decay for N = 126 waiting point nuclei. These calculations predict a large β-delayed neutron emission probability for the N ∼ 126 r-process path nuclei, which have a high Q β value and low neutron separation energy. These astronomical models cover a range of realistic physical conditions of the r-process environments
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