| Abstrakt: |
The angular anisotropy of secondary neutrons in neutron emission spectra (NES) of even–even and even–odd target nuclei and in observed prompt fission neutron spectra (PFNS) of the even–odd 239Pu and 235U target nuclei is caused by the preequilibrium emission of neutrons in the reaction (n, nX)1 and its effect on the prefission neutron spectrum from (n, xnf) reactions. In the case of PFNS, the average energy of (n, nf)1 neutrons depends on the angle of emission with respect to the incident neutron beam θ; consequently, the fission cross section, the average number of prompt fission neutrons (PFN), and the total kinetic energy (TKE) of fission fragments also depend on θ. High sensitivity to emission of (n, xnf)1 neutrons in the forward and backward hemispheres is predicted for the reaction 233U(n, F). Exclusive prefission neutron spectra from reactions 233U(n, xnf)1,...x and exclusive neutron spectra from (n, nγ) and (n, xn)1,...x are calculated within the Hauser–Feshbach formalism together with the cross sections for the (n,F) and (n,хn) reactions with allowance for the angular dependence of the first neutron emission in 233U(n, nX)1. Calculated exclusive neutron spectra of 233U(n, xnf)1,...x for θ ~ 90° agree with the consistent description of the observed 233, 232U(n, F) fission cross sections for neutrons with an energy of En ~ 0.01–20 MeV. An approximation of the angular PFNS anisotropy obtained for 239Pu(n, F) and 235U(n, F) allows correlating the angular anisotropy of 233U(n, xnf)1 neutrons with the contribution of the 233U(n, xnf) emission fission to the observed 233U(n, F) fission cross section. The ratio of average PFNS energies is obtained for forward and backward emission of (n, xnf)1 in the reaction 233U(n, xnf), which is much larger than for the 239Pu(n, F) and 235U(n, F) reactions. [ABSTRACT FROM AUTHOR] |
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