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

Abstract

Time-of-flight mass measurements of neutron-rich chromium isotopes up to N=40 and implications for the accreted neutron star crust We present the mass excesses of 59−64 Cr, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The mass of 64 Cr was 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 f p-shell, including the g 9/2 and d 5/2 orbits for the neutron valence space. We employ our result for the mass of 64 Cr 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 over 1 MeV reduction in binding for 64 Cr with respect to values from commonly used global mass models. I. INTRODUCTION 22The evolution of nuclear structure away from the val- production of more neutron-rich nuclides of interest were 106 used alternately, keeping Bρ of the A1900 and S800 fixed. 107Fragments were transmitted through the A1900 fragment spectively. 124The relationship between TOF and nuclear rest mass 125 m rest is obtained from the equation of motion for a 126 charged massive particle through a magnetic system. 127Equating the two counteracting forces, the Lorentz force 128 F L and the centripetal force F c , results in the followingwhere the Lorentz factor γ is a function of velocity v, the Bρ-corrected data were fit with a Gaussian distribu-158 tion in order to determine a mean TOF for each nuclide. 159The relationship between mass over charge m rest /q and 160TOF was fit to the data of reference nuclides in order to

Changes in nuclear structure along the Mn isotopic chain studied via charge radii

“…5 the mean-square charge radii r 2 of the 50−64 Mn isotopes (N = 25 − 39) are plotted along with the charge radii of the neighboring isotopes between 19 K and 29 Cu. For Mn the results from the atomic transition are shown except for 50,51,52,54,56 Mn for which only ionic data is available. The r 2 values are obtained with the reference radii of Fricke and Heilig [36] and the published changes in mean-square charge radii [12,23,[37][38][39][40].…”

“…Cr isotopes. However, new measurements show a much smoother behavior[52] although the reported errors are relatively large. High-precision mass measurements are required to clarify the issue.…”

Shell-model based study of the direct capture in neutron-rich nuclei

“…The SDPF-U interaction was designed to describe the neutron-rich nuclei around N = 28 in a 0hω space, therefore, it is applicable to nuclei with 8 ≤ Z ≤ 20 and 20 ≤ N ≤ 40, covering perfectly the region chosen for this study. The interaction was first used to describe the vanishing of the N = 28 shell-closure below 48 Ca and predicted correctly the deformation of 42 Si [21] and the spectroscopic factors of 46 Ar [22]. Since its publication it was frequently applied to this region of nuclei with a great success, for example it reproduces The LNPS interaction [31] defined in the proton p f -neutron p f 9/2d 5/2 space was first introduced to describe the onset of deformation below the N = 40, known as the second island of inversion.…”

Nuclear physics of the outer layers of accreting neutron stars

“…Recently, such constraints have been the province of time-of-flight mass measurements, as this technique is able to access the most exotic nuclides as compared to alternatives [228]. Already such measurements have constrained the heating for some of the strongest heating sources [217,229] and ruled-out Urca cooling for 56 Ti ↔ 56 Sc [218], which was once thought to be the strongest cooling source [24].…”