The location of electron capture heat sources in the crust of accreting neutron stars depends on the masses of extremely neutron-rich nuclei. We present first results from a new implementation of the time-of-flight technique to measure nuclear masses of rare isotopes at the National Superconducting Cyclotron Laboratory. The masses of 16 neutron-rich nuclei in the scandium -- nickel range were determined simultaneously, improving the accuracy compared to previous data in 12 cases. The masses of 61{V}, 63{Cr}, 66{Mn}, and 74{Ni} were measured for the first time with mass excesses of −30.510(890) MeV, −35.280(650) MeV, −36.900(790) MeV, and −49.210(990) MeV, respectively. With the measurement of the 66Mn mass, the locations of the two dominant electron capture heat sources in the outer crust of accreting neutron stars that exhibit superbursts are now experimentally constrained. We find that the location of the 66Fe→66Mn electron capture transition occurs significantly closer to the surface than previously assumed because our new experimental Q-value is 2.1 MeV (2.6σ) smaller than predicted by the FRDM mass model.
@article{arxiv.1109.5200,
title = {Time-of-flight mass measurements for nuclear processes in neutron star crusts},
author = {A. Estrade and M. Matos and H. Schatz and A. M. Amthor and D. Bazin and M. Beard and A. Becerril and E. F. Brown and R. Cyburt and T. Elliot and A. Gade and D. Galaviz and S. George and S. S. Gupta and W. R. Hix and R. Lau and G. Lorusso and P. Moller and J. Pereira and M. Portillo and A. M. Rogers and D. Shapira and E. Smith and A. Stolz and M. Wallace and M. Wiescher},
journal= {arXiv preprint arXiv:1109.5200},
year = {2015}
}