Electron Capture-delayed neutron-emissions in neutron star crust simulations using a Hauser-Feshbach model

Journal Article · Thu Apr 17 00:00:00 EDT 2008 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2920735· OSTI ID:21143155

Gupta, Sanjib S; Heger, A; Moeller, P; Kawano, T ^[1]

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1. Theoretical Division, Los Alamos National Laboratories, Los Alamos, NM 87545 (United States)

Recently, Electron Captures (henceforth EC) into excited states of neutron-rich nuclei were shown by the LANL-Michigan State-Mainz collaboration to result in Neutron Star (henceforth NS) Crust heating which was 4-5 times that of previous calculations. That result also highlighted the importance of a spread in X-ray burst abundances over several mass chains which could contribute to substantial heating through large shell and sub-shell gaps showing up in the excitation energy spectrum of the EC daughter. Such effects did not dominate when a single beta-stable species was evolved in an accreted parcel of matter in earlier calculations. We are now exploring the nucleosynthesis and heating from neutron processes deeper in the NS Crust around 10{sup 11} gcm{sup -3}. Electron captures into excited states of neutron-rich nuclei above neutron separation energies requires a Hauser-Feshbach code to calculate the branchings between 1-, 2-, 3-,...neutron emission rates in the stellar environment. Since the evolving composition has a free neutron fraction at a very density, the equilibrium composition at a given depth requires readjustments with respect to both the electron chemical potential and the neutron chemical potential, and the emitted neutrons can be captured into other mass chains with a net release of heat. From a nucleosynthesis perspective, we have a very interesting and hitherto unexplored pattern of weak interactions and neutron processes similar to the r-process, with the exception that the weak processes are primarily density-driven in the rather cold crust (T{sub 9} = 0.4-0.6) and in the {beta}{sup +} direction, that is, toward increasing neutron richness.

• OSTI ID: 21143155
• Journal Information: AIP Conference Proceedings, Vol. 1005, Issue 1; Conference: CNR 2007: 2007 international workshop on compound-nuclear reactions and related topics, Yosemite National Park, CA (United States), 22-26 Oct 2007; Other Information: DOI: 10.1063/1.2920735; (c) 2008 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
BINARY STARS
BRANCHING RATIO
COMPUTERIZED SIMULATION
DELAYED NEUTRONS
ELECTRON CAPTURE
ELECTRONS
ENERGY SPECTRA
EXCITATION
EXCITED STATES
HAUSER-FESHBACH THEORY
NEUTRON EMISSION
NEUTRON SEPARATION ENERGY
NEUTRON STARS
NEUTRON-RICH ISOTOPES
NUCLEOSYNTHESIS
POTENTIALS
R PROCESS
WEAK INTERACTIONS