Evaluation of nuclear reaction cross section of isotopes of some transuranium elements using OPTMAN code

Abstract

Coupled-channels optical model code OPTMAN is used as an alternative to experimental approach to evaluate the total reaction cross section for four selected isotopes of heavy rotational nuclei of the transuranium elements at energy 10 to 20 MeV. The selected isotopes are the 237Np, 243Am, 244Cm and 245Am. Their choice is as a result of their importance in the modern day nuclear reactor and the energy 10 – 20 MeV is the energy range of neutron produced in neutron generators and the maximum energy possessed by neutrons which are born in fission reaction. Total nuclear reaction cross section obtained in this work is much closer to the ENDF values such that the difference in values is less than 1 % at energy of 14 MeV and above for 237Np, 16 MeV and above for 243Am and at 18 MeV and above for 244Cm and 245Am. It is confirmed that the use of the rigid rotator is no longer a preferable approach in precise evaluations of nuclear reaction cross sections of heavy isotopes, the nucleus of transuranium elements is symmetric and the activities of rotation and vibrations (β – quadrupole, octupole vibrations and γ – quadrupole vibrations) cannot be ignored. The effects of the collective characteristics are exhibited by the neutrons and countered by the protons. This work compared well with the 6 % of Basunia in 2009 and 5 % of Paradela in 2011 using indirect measurement based on the surrogate ratio method and ECIS code respectively. Results of this work agree with about 1.3 % increase in accuracy.