학술논문
Experimental $\gamma$-decay strength in $^{59, 60}$Ni compared with microscopic calculations
Document Type
Working Paper
Author
Renstrøm, T.; Tveten, G. M.; Midtbø, J. E.; Utsunomiya, H.; Achakovskiy, O.; Kamerdzhiev, S.; Brown, B. Alex; Avdeenkov, A.; Ari-izumi, T.; Görgen, A.; Grimes, S. M.; Guttormsen, M.; Hagen, T. W.; Ingeberg, V. W.; Katayama, S.; Kheswa, B. V.; Larsen, A. C.; Lui, Y. -W.; Nyhus, H. -T.; Siem, S.; Symochko, D.; Takenaka, D.; Voinov, A. V.
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Subject
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Abstract
Nuclear level densities and $\gamma$-ray strength functions have been extracted for $^{59, 60}\rm{Ni}$, using the Oslo method on data sets from the $^{60}$Ni($^{3}$He,$^{3}$He$^{\prime}\gamma$)$^{60}$Ni and $^{60}$Ni($^{3}$He,$\alpha\gamma$)$^{59}$Ni reactions. Above the neutron separation energy, S$_n$, we have measured the $\gamma$-ray strength functions for $^{61}$Ni and $^{60}$Ni in photoneutron experiments. The low-energy part of the $^{59,60}$Ni $\gamma$-ray strength functions show an increase for decreasing $\gamma$ energies. The experimental $\gamma$-ray strength functions are compared with $M1$ $\gamma$-ray strength functions calculated within the shell model. The $E1$ $\gamma$-ray strength function of $^{60}$Ni has been calculated using the QTBA framework. The QTBA calculations describe the data above $E_{\gamma}\approx$ 7 MeV, while the shell-model calculations agree qualitatively with the low energy part of the $\gamma$-ray strength function. Hence, we give a plausible explanation of the observed shape of the $\gamma$-decay strength.