NUCLEAR LEVELS IN NP-238

Low and high energy spectra from thermal neutron capture in 237Np have been studied over the energy ranges 25 to 650 keV and 2600 to 5500 keV. Primary transitions from neutron capture in four resonances have been observed between about 4800 and 5400 keV. Using 12 MeV deuterons, (d, p) spectra at three angles have been observed with a magnetic spectrograph. A nuclear level scheme for 238Np has been constructed by combining the results of the above measurements with previous data from a study of the 242mAm α-decay. The Nilsson model has been used to interpret the level structure. Including results from the previous α-decay study, nine rotational bands can be assigned. The Nilsson configurations (Kπ [Nn3ΛΣ]) and band-head energies are: 2+ π[642↑]-ν[631↓], 0.0 keV; 3+ π[642↑]+ν[631↓], 86.6 keV; 3- π[523↓]+ν[631↓], 136.0 keV; 2- π[523↓]-ν[631↓], 182.8 keV; 5+ π[642↑]+ν[622↑], 278.1 keV; 0+ π[642↑]-ν[622↑], 332.5 keV; 5- π[523↓]+ν[622↑], 342.6 keV; 0- π[523↓]-ν[622↑], 286.0 keV; 6- π[642↑]+ν[743↑], 301 keV. The measured (d, p) reaction cross sections are compared with theoretical calculations based on these assignments. The Gallagher-Moszkowski rule is found to be valid in the four cases where we have observed both parallel and antiparallel coupled bands with K+ = Ωp+Ωn and K- = |Ωp-Ωp|. The lowest levels of the two K = 0 bands have spin I = 1; Newby odd-even shifts can be determined in both cases. © 1979.