The 54,56Fe(n, p)54,56Mn reactions at En = 97 MeV

Supernova electron capture rates for 55Co and 56Ni

“…After experimental (n,p) data clearly indicated that the Gamow-Teller strength is not only quenched (usually by more than a factor 2 compared to the independent particle model), but also fragmented over several states at modest excitation energies in the daughter nucleus [5][6][7][8][9], the need for an improved theoretical description has soon been realized [10][11][12]. These studies have been performed within the conventional shell model diagonalization approach, however, in strongly restricted model spaces and with residual interactions, which turned out to neither reproduce the quenching nor the position of the GT strength sufficiently well.…”

Shell-model calculations of stellar weak interaction rates. I. Gamow-Teller distributions and spectra of nuclei in the mass range A = 45–65

“…Thus it follows that both, stellar electron capture and beta decay, are very sensitive to the distribution of the GT + strength (in this direction a proton is changed into a neutron). In the last decade, GT + strength distributions on nuclei in the mass range A = 50 − 65 have been studied experimentally via (n,p) charge-exchange reactions at forward angles and the experimental data [3][4][5][6][7] show that, in contrast to the independent particle model, the total GT + strength is quenched and fragmented over many final states in the daughter nucleus caused by residual nucleon-nucleon correlations. Importantly for the stellar weak reaction rates, the data indicate a systematic misplacement of the GT centroid adopted in the FFN parametrization.…”

Shell model monte carlo methods

“…Due to insufficient experimental information, the GT + transition rates have so far been treated only qualitatively in presupernova collapse simulations, assuming the GT + strength to reside in a single resonance, whose energy relative to the daughter ground state has been parametrized phenomenologically [89]; the total GT + strength has been taken from the single particle model. Recent (n, p) experiments [62]- [66], however, show that the GT + strength is fragmented over many states, while the total strength is significantly quenched compared to the single particle model (see section 8.1). (A recent update of the GT + rates for use in supernova simulations assumed a constant quenching factor of 2 [79]).…”

“…As first examples we have studied several nuclei ( 51 V, 54,56 Fe, 58,60,62 Ni, and 59 Co), for which the Gamow-Teller strength distribution in the daughter nucleus is known from (n, p) experiments [62]- [66]. Note that the electron capture by these nuclei, however, plays only a minor role in the presupernova collapse.…”

“…[89,79], the Gamow-Teller contributions to the electron capture rates under typical presupernova conditions have been calculated assuming that the electrons obey a Fermi-Dirac distribution with a chemical potential adopted from the stellar trajectory at the electron-to-nucleon ratio corresponding to the respective nucleus [79]. The calculation have been performed for both the SMMC and experimental GT + strength distributions [62]- [66]. The electron capture rates so obtained agree within a factor of two for temperatures T = (3 − 5) × 10 9 Kelvin, which is the relevant temperature regime in the presupernova collapse [79] (Fig.…”