title: Mass Measurement of 56Sc Reveals a Small A = 56 Odd-Even Mass Staggering, Implying a Cooler Accreted Neutron Star Crust.
abstract: We present the mass excesses of (52-57)Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)((-54)(+0))  MeV and -21.0(1.3)  MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We find that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A≈56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Meisel
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.|Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: George
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: S
authors.initials: S
authors.lastname: Ahn
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: D
authors.initials: D
authors.lastname: Bazin
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Brown
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: J
authors.initials: J
authors.lastname: Browne
authors.affiliation: Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Carpino
authors.affiliation: Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008, USA.
authors.forename: H
authors.initials: H
authors.lastname: Chung
authors.affiliation: Physics Department, Kalamazoo College, Kalamazoo, Michigan 49006, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Cole
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: R H
authors.initials: RH
authors.lastname: Cyburt
authors.affiliation: School of Physics and Astronomy, The University of Edinburgh, EH8 9YL Edinburgh, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Estradé
authors.affiliation: Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008, USA.
authors.forename: M
authors.initials: M
authors.lastname: Famiano
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: A
authors.initials: A
authors.lastname: Gade
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: C
authors.initials: C
authors.lastname: Langer
authors.affiliation: Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
authors.forename: M
authors.initials: M
authors.lastname: Matoš
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: W
authors.initials: W
authors.lastname: Mittig
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: F
authors.initials: F
authors.lastname: Montes
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Morrissey
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: J
authors.initials: J
authors.lastname: Pereira
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: H
authors.initials: H
authors.lastname: Schatz
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: J
authors.initials: J
authors.lastname: Schatz
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: M
authors.initials: M
authors.lastname: Scott
authors.affiliation: Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
authors.forename: D
authors.initials: D
authors.lastname: Shapira
authors.affiliation: Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: K
authors.initials: K
authors.lastname: Smith
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: J
authors.initials: J
authors.lastname: Stevens
authors.affiliation: Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA.
authors.forename: W
authors.initials: W
authors.lastname: Tan
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: O
authors.initials: O
authors.lastname: Tarasov
authors.affiliation: Department of Physics, Western Michigan University, Kalamazoo, Michigan 49008, USA.
authors.forename: S
authors.initials: S
authors.lastname: Towers
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: K
authors.initials: K
authors.lastname: Wimmer
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Winkelbauer
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: J
authors.initials: J
authors.lastname: Yurkon
authors.affiliation: National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.|Department of Physics and Astronomy, Michigan State University, East Lansing, Michigan 48824, USA.|Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: R G T
authors.initials: RG
authors.lastname: Zegers