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

• Published in: arXiv.org 2016-03
• Main Authors: Meisel, Z, George, S, Ahn, S, Bazin, D, Brown, B A, Browne, J, Carpino, J F, Chung, H, Cyburt, R H, Estradé, A, Famiano, M, Gade, A, Langer, C, Matoš, M, Mittig, W, Montes, F, Morrissey, D J, Pereira, J, Schatz, H, Schatz, J, Scott, M, Shapira, D, Sieja, K, Smith, K, Stevens, J, Tan, W, Tarasov, O, Towers, S, Wimmer, K, Winkelbauer, J R, Yurkon, J, Zegers, R G T
• Format: Article
• Language: English
• Subjects: Atomic properties; Binding; Chromium isotopes; Cyclotrons; Heating; Neutron stars; Neutrons; Reduction; Time measurement
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1603.07614

We present the mass excesses of 59-64Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64Cr 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 64Cr 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 64Cr with respect to values from commonly used global mass models.