Speaker
Mr
Daniel Galaviz Redondo
(CSIC)
Description
Type I X-ray bursts, thermonuclear runaways on the surface of an accreting
neutron star in a binary system, are one of the known sites for the rapid proton
capture process (rp-process)[1,2]. After accumulation of material, mainly
hydrogen and helium, on the surface of the neutron star, the triple-alpha
reaction triggers a series of fast (a,p) and (p,g) reactions, with subsequent
beta decays, that drive the process along the proton-rich side of the valley of
stability. The process stops around the Sn-Te region [3], and after ther
hydrogen is depleted, the produced nuclei decay B+ and fall onto the surface of
the neutron star.
Proton capture rates are a key ingredient in the description of the energy
release curve associated to X-ray bursts, as well as in the determination of the
final isotopic abundance distribution [4]. In order to reduce the uncertainties in
the determination of (p,g) reaction rates, several experiments were performed
at the National Superconducting Cyclotron Laboratory (NSCL) at the Michigan
State University, using radioactive beams, to determine precisely the level
structure above the proton threshold of rp process nuclei.
This work presents the experimental approach and the set-up at the NSCL,
which involves the S800 Spectrograph and the Segmented Germanium Array
(SeGA), as well as the first results obtained with this technique. Implications of
the new results in the astrophysical rp process are also discussed.
[1] R. K. Wallace, and S. E. Woosley, Astrophys. J. (Suppl.) 45, 389 (1981)
[2] H. Schatz et al., Phys. Rep. 294, 167 (1998)
[3] H. Schatz et al., Phys. Rev. Lett. 86, 3471 (2001)
[4] J. L. Fisker et al., Astrophys. J. Lett. 608L, 61 (2004)
Author
Mr
Daniel Galaviz Redondo
(CSIC)
