Nuclear level densities and $\gamma -$ray strength functions of ${}^{111,112,113}$Sn isotopes studied with the Oslo method

Abstract

The ${}^{111,112,113}$Sn isotopes have been studied with ($p,d\gamma$), ($p,p^{\prime }\gamma$), and ($d,p\gamma$) reactions to extract the nuclear level densities (NLDs) and $\gamma$-ray strength functions (GSFs) of these nuclei below the neutron separation energy by means of the Oslo method. The experimental NLDs for all three nuclei demonstrate a trend compatible with the constant-temperature model below the neutron separation energy while also being in good agreement with the NLDs of neighboring Sn isotopes, obtained previously with the Oslo-type and neutron evaporation experiments. The extracted microcanonical entropies yield $\approx 1.5$ $k_B$ entropy of a valence neutron in both ${}^{111}$Sn and ${}^{113}$Sn. Moreover, the deduced microcanonical temperatures indeed suggest a clear constant-temperature behavior above $\approx$ 3 MeV in ${}^{111,113}$Sn and above $\approx$ 4.5 MeV in ${}^{112}$Sn. We observe signatures for the first broken neutron pairs between 2 and 4 MeV in all three nuclei. The GSFs obtained with the Oslo method are found to be in good agreement below the neutron threshold with the strengths of ${}^{112,114}$Sn extracted in the ($p,p^{\prime }$) Coulomb excitation experiments.

arXiv comment13 pages, 9 figures

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