Influence of Rb73 on the ashes of accreting neutron stars

We find that the proton separation energy, S(p), of Rb-73 is -640(40) keV, deduced from the observation of beta-delayed ground-state protons following the decay of Sr-73. This lower-limit determination of the proton separation energy of Rb-73 coupled with previous upper limits from nonobservation, provides a full constraint on the mass excess with Delta M(Rb-73) = -46.01 +/- 0.04 MeV. With this new mass excess and the excitation energy of the J(pi) = 5/2(-) isobaric-analog state (T = 3/2) in Rb-73, an improved constraint can be put on the mass excess of Sr-73 using the isobaric-multiplet mass equation (IMME), and we find Delta M(Sr-73) = -31.98 +/- 0.37 MeV. These new data were then used to study the composition of ashes on accreting neutron stars following Type I xray bursts. Counterintuitively, we find that there should be an enhanced fraction of A > 102 nuclei with more negative proton separation energies at the Kr-72 rp-process waiting point. Larger impurities of heavier nuclei in the ashes of accreting neutron stars will impact the cooling models for such astrophysical scenarios.