Advanced Evaluation of 237Np and 243Am Neutron Data

V. M. Maslov, N. A. Tetereva, V. G. Pronyaev, T. Granier and F.-J. Hambsch

J. Korean Phys.Soc. 59,867 [doi: 10.3938/jkps.59.867 | PDF Download]

The diverse measured data base of n+237Np is evaluated using a generalized least squares code and statistical theory of nuclear reactions. Consistent description of the total, fission and partial inelastic scattering data in 1 - 3 MeV energy range provides an important constraint for the absorption cross section. Important constraints for the measured capture cross section come from the average radiation S0 and S1 strength functions. An abrupt change of the inelastic data shape at En ∼ 1.5 MeV is explained by the sharp increase of the level density of the residual odd-even nuclide 237Np due to the onset of three-quasi-particle excitations. The in fluence of exclusive (n, xnf) pre-fission neutrons on prompt fission neutron spectra and (n, xn) reactions spectra is modeled. Contributions of emissive/non-emissive fission and exclusive spectra of (n, xnf) reactions are defined by a consistent description of the 237Np(n, F), 237Np (n, 2n)236sNp reactions and the ratio of the yields of short-lived isomer (1-) and long-lived ground (6-) 236Np states measured at ∼14 MeV. The isomer ratio of the yields of short-lived ground (1-) 242gAm and long-lived isomer (5-) 242mAm states in 243Am(n, 2n) reaction is calculated modeling the gamma-decay of the possible Gallaher-Moshkowski doublet states of 242Am.