Allowed and forbidden beta-decay log ft values of neutron-rich Pb and Bi isotopes

TL;DR

This paper estimates beta-decay log ft values for neutron-rich lead and bismuth isotopes using the pn-QRPA model, compares them with experimental data, and calculates decay rates in stellar environments, highlighting the significance of forbidden transitions.

Contribution

It applies the pn-QRPA model with Woods Saxon potential to neutron-rich isotopes and extends calculations to stellar conditions, including forbidden transitions, which are often overlooked.

Findings

Calculated log ft values closely match experimental data.

Forbidden transitions can dominate decay rates in stellar environments.

Temperature influences allowed and forbidden decay rates differently.

Abstract

The beta-decay log ft values for 210 215Pb 210 215Bi and 210 215Bi 210 215Po transitions in the north east region of 208Pb nuclei are estimated using the proton neutron quasiparticle random phase approximation model. The pn-QRPA equations were solved using the schematic model approach. The Woods Saxon (WS) potential was inserted as a mean field basis and nuclei were treated as spherical. Allowed Gamow Teller (GT) and first forbidden (FF) transitions were investigated in the particle hole (ph) channel. The calculated log ft values of the allowed GT and FF transitions using the pn-QRPA(WS) were found closer to the experimental values. Later we performed calculation of beta-decay rates in stellar environment. Here we solved the RPA equations in deformed Nilsson basis, both in the particle particle (pp) and particle hole (ph) channels. Allowed beta decay and unique first-forbidden (U1F) rates were calculated in stellar matter. For certain cases, the calculated U1F contribution was much more than the allowed beta decay rates under prevailing stellar conditions in line with previous findings. Increasing temperature of the stellar core affected the allowed GT rates more than the U1F rates.