# Experimental Constraint on Stellar Electron-Capture Rates from the ${}^{88}\text{Sr}(t,{}^{3}\text{He}+\gamma){}^{88}\text{Rb}$ reaction at 115 MeV/u

## TL;DR

This study measures Gamow-Teller strength in ${}^{88}$Sr to refine electron-capture rate estimates crucial for supernova modeling, revealing significantly lower rates than traditional approximations and providing a benchmark for theoretical models.

## Contribution

The paper provides the first experimental Gamow-Teller strength distribution for ${}^{88}$Sr at 115 MeV/u, challenging existing single-state approximation rates used in astrophysics.

## Key findings

- Measured strength below 8 MeV was consistent with zero.
- Derived electron-capture rate is over ten times smaller than single-state approximation.
- Shell-model and QRPA calculations align better with data, highlighting the importance of complex nuclear effects.

## Abstract

The Gamow-Teller strength distribution from ${}^{88}$Sr was extracted from a $(t,{}^{3}\text{He}+\gamma)$ experiment at 115 MeV/$u$ to constrain estimates for the electron-capture rates on nuclei around $N=50$, between and including $^{78}$Ni and $^{88}$Sr, which are important for the late evolution of core-collapse supernovae. The observed strength below an excitation energy of 8 MeV was consistent with zero and below 10 MeV amounted to $0.1\pm0.05$. Except for a very-weak transition that could come from the 2.231-MeV $1^{+}$ state, no $\gamma$ lines that could be associated with the decay of known $1^{+}$ states were identified. The derived electron-capture rate from the measured strength distribution is more than an order of magnitude smaller than rates based on the single-state approximation presently used in astrophysical simulations for most nuclei near $N=50$. Rates based on shell-model and quasiparticle random-phase approximation calculations that account for Pauli blocking and core-polarization effects provide better estimates than the single-state approximation, although a relatively strong transition to the first $1^{+}$ state in $^{88}$Rb is not observed in the data. Pauli unblocking effects due to high stellar temperatures could partially counter the low electron-capture rates. The new data serves as a zero-temperature benchmark for constraining models used to estimate such effects.