Gamow-Teller strength distributions for nuclei in presupernova stellar cores

Abstract

Electron-capture and β-decay of nuclei in the core of massive stars play an important role in the stages leading to a type II supernova explosion. Nuclei in the f-p shell are particularly important for these reactions in the post Siliconburning stage of a presupernova star. In this paper, we characterise the energy distribution of the Gamow-Teller Giant Resonance (GTGR) for midfp-shell nuclei in terms of a few shape parameters, using data obtained from high energy, forward scattering (p,n) and (n,p) reactions. The energy of the GTGR centroid E GT is further generalised as function of nuclear properties like mass number, isospin and other shell model properties of the nucleus.Since a large fraction of the GT strength lies in the GTGR region, and the GTGR is accessible for weak transitions taking place at energies relevant to the cores of presupernova and collapsing stars, our results are relevant to the study of important e − -capture and β-decay rates of arbitrary, neutron-rich, fp shell nuclei in stellar cores. Using the observed GTGR and Isobaric Analog States (IAS) energy systematics we compare the coupling coefficients in the Bohr-Mottelson two particle interaction Hamiltonian for different regions of the Isotope Table. Ms number PACS number: 97.10.Cv, 23.40.-S, 97.60.Bw

Neutrino Spectroscopy of the Early Phase of Nearby Supernovae

“…The Q value, assuming that the strength is concentrated in a single state, is given as Q ͑m 1 1.297 1 E GT ͒, wherê m ( m n 2 m p ) is the difference in the neutron and proton chemical potentials when free nucleons coexist with a distribution of neutron rich nuclei in nuclear statistical equilibrium, and E GT is the energy of the Gamow-Teller (GT) resonance centroid. The centroids in fp-shell nuclei, found from experimental data from ͑n, p͒ reactions, have been used for characterizing GT transitions in these nuclei [17] and are close to the value (3 MeV) used here. The Fermi energy m e 11.1͑r 10 Y e ͒ 1͞3 MeV.…”

Half-lives and presupernova weak interaction rates for nuclei away from the stability line

“…The centroid of this Gaussian is fixed from the results of (p,n) reaction studies and a phenomenological formula for its position involving (N − Z) and A 1/3 is employed [9]. Recently, Sutaria and Ray [10] improved this by using a fit to new data with mostly fp shell nuclei and a calculation of rates based on their centroids is being persued. The strength width coming from the nuclear…”

Centroids of Gamow–Teller Transitions at Finite Temperature in fp-shell Neutron-rich Nuclei

“…(7), of the energy centroid for GT + excitations for different values of the temperature (T). The experimentally determined energy centroids, (E exp ), are taken from the compilation of data given in ref 5). .…”

“…The dependence of such nuclear observables upon the stellar temperature is a matter of interest [4]. In the present letter we are addressing the question about the temperature dependence of the energy-centroids of GT ± transitions [5].…”

“…On the other hand the neutrino induced r-process reactions will remain relatively unaffected by the small ( ≤ 0.5 MeV) thermally induced shifts of GT − centroids. Considering that the empirically determined energies of the GT + centroids are known with an accuracy of the order of 0.43 MeV [5] the temperaturedependent effects reported here may be significant for astrophysical rate calculations and their consequences for pre-supernova stellar evolution and gravitational collapse. Work is in progress to predict GT + (GT − ) centroids and strengths, by using the pn-QRPA method at finite T, for nuclei for which experimental data through charge-exchange (p,n)( (n,p))-reactions in the opposite direction is available to constrain the former one.…”