$\beta$-decay Measurements Near the $N=40$ Island of Inversion to Quantify Cooling of Accreted Neutron Star Crusts

K. Hermansen; W. -J. Ong; H. Schatz; J. Browne; A. Chester; K. Childers; R. Jain; S. Liddick; S. Lyons; S. A. Miskovich; P. Möller; F. Montes; J. Owens-Fryar; A. Palmisano-Kyle; A. L. Richard; N. Rijal; M. Smith; D. Soltesz; A. Spyrou; S. K. Subedi; L. Wagner

arXiv · 2603.22669

$\beta$-decay Measurements Near the $N=40$ Island of Inversion to Quantify Cooling of Accreted Neutron Star Crusts

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Abstract

Understanding the thermal structure of the outer crust of accreting neutron stars is important to interpret astronomical X-ray observations. Ground-state to ground-state $\beta$-decay transitions of neutron-rich nuclei comprising the crust enable Urca neutrino cooling processes that affect this thermal structure. Here we constrain the ground-state to ground-state transition strengths for the decays of $^{57}$Sc, $^{57}$Ti, and $^{59}$Ti based on experimental data. The data were obtained by combining total absorption $\gamma$-spectroscopy data from the SuN detection system with $\beta$-delayed neutron emission data from the NERO detection system at Michigan State University's National Superconducting Cyclotron Laboratory. We find $\log ft=$5.8$^{+0.3}_{-0.2}$ and $\log ft=$5.34$^{+0.08}_{-0.24}$ for the decays of $^{57}$Ti and $^{59}$Ti, respectively, and find no evidence for ground-state feeding in the decay of $^{57}$Sc. The results indicate weaker transitions than predicted by theory and indicated by previous measurements, resulting in reduced efficiency of neutrino cooling in accreted neutron star crusts in systems that exhibit X-ray superbursts.

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K. Hermansen, W. -J. Ong, H. Schatz, J. Browne, A. Chester, K. Childers, R. Jain, S. Liddick, S. Lyons, S. A. Miskovich, P. Möller, F. Montes, J. Owens-Fryar, A. Palmisano-Kyle, A. L. Richard, N. Rijal, M. Smith, D. Soltesz, A. Spyrou, S. K. Subedi, L. Wagner. 2026-03-24. $\beta$-decay Measurements Near the $N=40$ Island of Inversion to Quantify Cooling of Accreted Neutron Star Crusts. https://arxiv.org/abs/2603.22669

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