Speaker
Description
Fast neutron induced nuclear reaction cross section data are necessary for both nuclear energy technology and the study of nuclear physics research. The information of (n,2n) cross sections is quite essential in nuclear reactor technology as a significant portion of the fission neutron spectrum lies above the threshold of (n,2n) reaction for most structural materials. Furthermore, the application of the fast neutron induced nuclear reaction cross section data have been increasing in the fields of biomedical applications, accelerator driven transmutation, material irradiation experiments concerning research and development for fusion reactor technology. On the other hand, systematics of fast neutron induced reaction cross sections is useful to clarify nuclear reaction mechanisms. Also, it is often necessary, in practice, to use the systematical analysis for evaluation of the neutron cross sections of the nuclides, for which no experimental data are available.
A systematic dependence of (n,2n) reaction cross sections on the neutron number excess parameter (N-Z)/A for target nuclei was studied in a number of works. Purely empirical formulaeand semi-empirical formulae based on the statistical model, pre-equilibriumand direct reaction mechanismswere suggested to explain this regular behaviour of the (n,2n) cross sections. However, a strict and unified theoretical validity no up to now is available for explanation of the neutron cross section regularity which in the literature is termed as the isotopic effect.
In this work new formulae for the (n,2n) cross section are deduced using the concepts of statistical and non-statistical nuclear reaction mechanisms. In the calculation of the statistical share of the cross section the constant nuclear temperature approximation, evaporation model and Weizsäcker’s formula for binding energy were utilized. Non-statistical part was obtained by subtraction of statistical model cross section from total one. The total cross section was determined by geometrical cross section of target nuclei as an upper limit of interaction of neutrons with nuclei.
It was shown that non-statistical part of the (n,2n) cross section is in agreement with known experimental data taken from EXFOR library.