"Early-time observations of cooling crusts of neutron stars in Quasi-persistent X-ray transients cannot be explained by current astrophysical models, suggesting an incomplete understanding of the physical and nuclear processes that occur in the crust. An as yet unidentified strong, shallow heat source has been postulated to account for these discrepancies. Complicating this issue is the recent discovery of Urca cooling, beta decay-electron capture cycles that release neutrinos, in neutron star crusts. The strength of Urca cooling depends critically on the magnitude of the ground state to ground state transition between the parent-daughter pair, because the electron degeneracy under neutron star crustal conditions forbids beta decay transitions to excited states. Current predictions of Urca cooling in neutron star crusts are highly reliant on theoretical QRPA predictions. Experimental data are needed to test these predictions and characterise their uncertainties. Of particular importance is the possible existence of strong ground state to ground state electron capture and beta decay transitions, and the strength of these transitions. This work reports an experimental measurement of the transition strength for the beta decay of the ground state of 61V to states in 61Cr. Most importantly, the ground state to ground state transition strength was determined to be 7.4+13.8 -5.8 % (corresponding to a log f t value of 5.5+0.8 -0.6 ). This result confirms the existence of a considerable ground state to ground state transition that enables Urca cycle cooling in accreted neutron star crusts at the boundary of the 61Cr and 61V layers. However, the log f t value is significantly larger than the theoretically predicted log f t value of 4.35, resulting in a slower than expected Urca cycle. This result was achieved through the measurement of the beta-delayed gamma rays using the total absorption spectrometer SuN and the measurement of the beta-delayed neutron branch using the neutron long counter system NERO at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The use of the combination of SuN and NERO helps to mitigate the impact of the Pandemonium effect that tends to significantly skew studies using more traditional high-resolution, low-efficiency detectors. The impact of this experimental result on the cooling strength of the A = 61 mass chain was investigated using a nucleosynthesis network evolved under neutron star crustal conditions. The results show that the mass 61 chain is amongst the strongest cooling chains in crusts composed of X-ray burst ashes. Updated cooling strengths using the latest state of experimental knowledge were also folded over realistic crust compositions for X-ray bursting systems to identify other strong cooling chains, as well as to pinpoint Urca pairs of particular interest for future studies using the same technique as developed in this work."--Pages ii-iii.
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