Level densities and $γ$-ray strength functions in Sn isotopes - Nuclear ExperimentReport as inadecuate

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Abstract: The nuclear level densities of $^{118,119}$Sn and the $\gamma$-ray strengthfunctions of $^{116,118,119}$Sn below the neutron separation energy areextracted with the Oslo method using the $^3$He, \,$\alpha \gamma$ and$^3$He,$^3$He$^\prime\gamma$ reactions. The level density function of$^{119}$Sn displays step-like structures. The microcanonical entropies arededuced from the level densities, and the single neutron entropy of $^{119}$Snis determined to be $1.7 \pm 0.2\,k B$. Results from a combinatorial modelsupport the interpretation that some of the low-energy steps in the leveldensity function are caused by neutron pair-breaking. An enhancement in all the$\gamma$-ray strength functions of $^{116-119}$Sn, compared to standard modelsfor radiative strength, is observed for the $\gamma$-ray energy region of$\simeq 4 -11$ MeV. These small resonances all have a centroid energy of8.01 MeV and an integrated strength corresponding to $1.79\%$ of theclassical Thomas-Reiche-Kuhn sum rule. The Sn resonances may be due to electricdipole neutron skin oscillations or to an enhancement of the giant magneticdipole resonance.

Author: H. K. Toft, A. C. Larsen, U. Agvaanluvsan, A. Bürger, M. Guttormsen, G. E. Mitchell, H. T. Nyhus, A. Schiller, S. Siem, N. U. H.

Source: https://arxiv.org/

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