Beta-decay Half Lives beyond $^{54}$Ca: A Systematic Survey of Decay Properties approaching the Neutron Dripline

TL;DR

This study measured 15 new half-lives of neutron-rich isotopes near $^{54}$Ca at FRIB, revealing unexpected systematic changes in decay properties approaching the neutron dripline and testing advanced theoretical models.

Contribution

It introduces a new method for extracting lifetimes considering unknown neutron emission branches and provides comprehensive experimental data to test shell-model and QRPA predictions.

Findings

Longer than expected half-lives beyond N=34.

Shell-model calculations explain observed trends.

QRPA model shows good agreement with experimental data.

Abstract

In an experiment performed at the Facility for Rare Isotope Beams (FRIB) using the FRIB Decay Station initiator (FDSi), 15 new half lives of isotopes near $^{54}$Ca were measured. A new method of extracting lifetimes from experimental data, taking into account the unknown $\beta$-delayed neutron emission branches of very neutron-rich nuclei, was developed to enable systematic uncertainty analysis. The experiment observed a dramatic change in the half-life systematics for the isotopes with neutron number N =34. Beyond N =34, the decline of nuclear lifetime is much slower, leading to longer than anticipated lifetimes for near-dripline nuclei. State-of-the-art shell-model calculations can explain the experimental results for Z$>$19 nuclei, revealing the imprint of shell effects and the need for modification of single-particle neutron states. The results from a newly developed QRPA model with potential for making global predictions were also tested against the experimental results and good agreement was found.