Level density and gamma-ray strength function in the odd-odd Np-238 nucleus

Tornyi, Tamás Gábor and Guttormsen, M. and Eriksen, T. K. and Goergen, A. and Giacoppo, F. and Hagen, T. W. and Krasznahorkay, Attila and Larsen, A. C. and Renstrom, T. and Rose, S. J. and Siem, S. and Tveten, G. M. (2014) Level density and gamma-ray strength function in the odd-odd Np-238 nucleus. PHYSICAL REVIEW C, 89 (4). ISSN 2469-9985

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Abstract

The level density and γ-ray strength function in the quasi-continuum of 238Np have been measured using the Oslo method. The level density function follows closely the constant-temperature level density formula and reaches 43 million levels per MeV at Sn = 5.488 MeV of excitation energy. The γ-ray strength function displays a two-humped resonance at low-energy as also seen in previous investigations of Th, Pa and U isotopes. The structure is interpreted as the scissors resonance and has an average centroid of ωSR = 2.26(5) MeV and a total strength of BSR = 10.8(12)µ 2 N , which is in excellent agreement with sum-rule estimates. The scissors resonance is shown to have an impact on the 237Np(n, γ) 238Np cross section.

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