Experimental gamow–teller strength in the β decay of the rp-process waiting-point nucleus 64Ge and its impact on stellar weak-decay rates

Abstract

The β decay of the rp -process waiting-point nucleus 64Ge plays a key role in Type-I X-ray bursts. Reliable theoretical predictions at the high temperatures and densities of these environments require models capable of reproducing the relevant Gamow–Teller (GT) strength under terrestrial conditions. We report a measurement of the B (GT) distribution in the decay of 64Ge using the Total Absorption Gamma-ray Spectroscopy technique at CERN-ISOLDE. The experimentally determined B (GT) distribution is compared with large-scale shell-model calculations and with existing theoretical approaches. While shell-model-based calculations provide a good description of the data, QRPA results show significant discrepancies. Stellar weak-decay rates derived from our experimental B (GT) distribution provide the first experimentally constrained rates for 64Ge, and a stringent benchmark for nuclear-structure models employed in rp-process simulations.