Time-of-flight mass measurements of neutron-rich chromium isotopes up to N=40 and implications for the accreted neutron star crust

Z. Meisel, S. George, S. Ahn, D. Bazin, B. A. Brown, J. Browne, J. F. Carpino, H. Chung, R. H. Cyburt, A. Estradé, M. Famiano, A. Gade, C. Langer, M. Matoš, W. Mittig, F. Montes, D. J. Morrissey, J. Pereira, H. Schatz, J. SchatzM. Scott, D. Shapira, K. Sieja, K. Smith, J. Stevens, W. Tan, O. Tarasov, S. Towers, K. Wimmer, J. R. Winkelbauer, J. Yurkon, R. G.T. Zegers

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Abstract

We present the mass excesses of Cr59-64, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of Cr64 is determined for the first time, with an atomic mass excess of -33.48(44) MeV. We find a significantly different two-neutron separation energy S2n trend for neutron-rich isotopes of chromium, removing the previously observed enhancement in binding at N=38. Additionally, we extend the S2n trend for chromium to N=40, revealing behavior consistent with the previously identified island of inversion in this region. We compare our results to state-of-the-art shell-model calculations performed with a modified Lenzi-Nowacki-Poves-Sieja interaction in the fp shell, including the g9/2 and d5/2 orbits for the neutron valence space. We employ our result for the mass of Cr64 in accreted neutron star crust network calculations and find a reduction in the strength and depth of electron-capture heating from the A=64 isobaric chain, resulting in a cooler than expected accreted neutron star crust. This reduced heating is found to be due to the >1-MeV reduction in binding for Cr64 with respect to values from commonly used global mass models.

Original languageEnglish
Article number035805
JournalPhysical Review C
Volume93
Issue number3
DOIs
StatePublished - Mar 22 2016

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