^235mU and ²³⁵U neutron-induced fission

Abstract
Neutron cross sections of ²³⁵U and ^235mU are obtained via Hauser-Feshbach model calculations. The cross section differences are attributed to the spectroscopic properties of the transition states at saddle deformations of ²³⁶U and the coupling strengths of the deformed optical potential for the target spin values 7/2^- and 1/2⁺. The ^235mU(n,f) cross section at E_n ≲ 0.1 MeV depends on the position of octupole states at outer saddle, being ~2 times lower than that of ²³⁵U(n,f) at E_n ~ 1 keV. The capture-to-fission ratio of ²³⁵U and ^235mU is affected at E_n ≲ 0.1 MeV, being ~2 times higher for the latter at E_n ~ 1 keV. ²³⁵U(n,xn) reaction cross sections and prompt fission neutron spectra (PFNS) are dependent on the emissive fission chances contributions to the observed σ(n,F) of ²³⁵U, which are much different from the latest evaluations of ENDF/B and JEFF. The role of exclusive pre-fission (n,xnf) neutron spectra for the ²³⁵U(n,F) PFNS description and prediction of PFNS for ²³⁹Pu(n,F) is exemplified.