Correlation between the Prompt Neutron Multiplicity and Prompt Gamma-ray Energy in the Frame of the Point-by-Point Model

Abstract

The Point-by-Point (PbP) model was used to calculate average prompt γ-ray energy and multiplicity as a function of fragment mass and total kinetic energy, Eγ(A,TKE), Eγ(A), Nγ(A), <Eγ>(TKE) for 252Cf(SF), 233,235U(nth,f) and 239Pu(nth,f). The results describe very well the experimental data including the linear correlation between the prompt γ-ray energy and prompt neutron multiplicity. Contrary to the experimentally observed increase of prompt neutron multiplicity ν(A) with incident neutron energy for heavy fragments only for 235U and 239Pu and confirmed by the PbP results for 234,235U, 237Np and 232Th, Eγ(A) does not exhibit a similar behaviour. Total <Eγ>, <Nγ>, <ɛγ> are obtained in overall good agreement with the experimental data measured in the 1970s – 1980s. The linear correlation <Eγ>=p<νp>+q revealed by the experimental data of Nifenecker, Pleasonton and Fréahut is well reproduced by the global parameterization of Vladuca and Tudora, 2001. This parameterization was deduced by fitting the results of the (n,n’) and (n,γ) competition obtained from nuclear reaction calculations (treated by spherical optical and Hauser-Feshbach statistical models) applied at that time on a limited number of nuclei appearing as fission fragments (in the frame of the 7 points approximation). The experimental Eγ>, <Nγ> and < ɛγ> data recently measured for 252Cf(SF) and 235U(nth,f) can be reproduced by keeping the slope provided by the global parameterization and an adjustment with about 7% for the intercept. This points to needed refinement of the global parameterization by e.g. new nuclear reaction calculations for light fission fragments isotopes.