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

The level density and gamma-ray strength function in the quasicontinuum of Np-238 have been measured using the Oslo method. The level-density function follows closely the constant-temperature level-density formula and reaches 43 x 10(6) levels per MeV at S-n = 5.488 MeV of excitation energy. The gamma-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 omega(SR) = 2.26(5) MeV and a total strength of B-SR = 10.8(12)mu(2)(N), which is in excellent agreement with sum-rule estimates. The scissors resonance is shown to have an impact on the Np-237(n, gamma)Np-238 cross section.