Evaluation of nuclear reaction cross section of some isotopes of plutonium at energy range 10-20 MeV 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 different isotopes of Plutonium as an example of heavy rotational nuclei of the transuranium elements over an energy range of 10 to 20 MeV. The selected isotopes are the ₉₄Pu²³⁸, ₉₄Pu²⁴⁰, ₉₄Pu²⁴¹, and ₉₄Pu²⁴². Their choice is as a result of their importance in the modern day nuclear reactor and the energy range 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. Results show that the percentage deviation of total cross section from ENDF values obtained for this work is less than 1 % at energy 16 MeV and above for ₉₄Pu²³⁸, ₉₄Pu²⁴⁰, and ₉₄Pu²⁴¹ while at 18 MeV and above for ₉₄Pu²⁴². This work confirms that the use of the rigid rotator is no longer a preferable approach in precise evaluations of nuclear reaction cross sections of heavy isotopes. It is observed that the nucleus of plutonium isotope is symmetric and the activities of rotation and vibrations (β – quadrupole, octupole vibrations and γ – quadrupole vibrations) cannot be ignored. This work compared well with the 6 % deviation of Basunia in 2009 and 5 % deviation of Paradela in 2011 using indirect measurement based on the surrogate ratio method and ECIS code respectively. The result of this work is found to agree with about 1 % increase in accuracy.