The nuclear level densities of 118,119Sn and the γ-ray strength functions of 116,118,119Sn below the neutron separation energy are extracted with the Oslo method using the (3He, \,αγ) and (3He,3He′γ) reactions. The level density function of 119Sn displays step-like structures. The microcanonical entropies are deduced from the level densities, and the single neutron entropy of 119Sn is determined to be (1.7±0.2)kB. Results from a combinatorial model support the interpretation that some of the low-energy steps in the level density function are caused by neutron pair-breaking. An enhancement in all the γ-ray strength functions of 116−119Sn, compared to standard models for radiative strength, is observed for the γ-ray energy region of ≃(4−11) MeV. These small resonances all have a centroid energy of 8.0(1) MeV and an integrated strength corresponding to 1.7(9)% of the classical Thomas-Reiche-Kuhn sum rule. The Sn resonances may be due to electric dipole neutron skin oscillations or to an enhancement of the giant magnetic dipole resonance.
@article{arxiv.1006.4781,
title = {Level densities and $\gamma$-ray strength functions in Sn isotopes},
author = {H. K. Toft and A. C. Larsen and U. Agvaanluvsan and A. Bürger and M. Guttormsen and G. E. Mitchell and H. T. Nyhus and A. Schiller and S. Siem and N. U. H. Syed and A. Voinov},
journal= {arXiv preprint arXiv:1006.4781},
year = {2014}
}