Achievements and Still Open Problems

Abstract

One may conclude that there are several points which may be demonstrated as real achievements. First of all, the Prompt Fission Neutron Spectra (PFNS) of ²⁵²Cf(sf) are proclaimed as “standard spectrum” with rather small uncertainties in the energy range < 10MeV. Many years’ efforts addressed to “create” dosimetry reactions, cross sections, and experimental investigations of average reaction cross sections in this neutron field confirmed this conclusion. The ratio R = C/E calculated to experimental average cross sections is 1.004 ± 0.020 in the energy range 1–15 MeV. It was confirmed (see previous chapters) that the average energy of the PFNS ²³⁵U(th) is known with high accuracy E = 1.974 ± 0.002 MeV. Recent theoretical investigations gave very interesting result: neutrons may have strong angular distribution relative to fission fragments (FFs) due to fast, non-adiabatic rupture of the fissile system. So, the orientation of the fission neutron along the FF direction is not the sign that they are emitted from moving fragments. However, many problems are still open: contradiction between macroscopic and microscopic experimental data for ²³⁵U(th) (mic–mac problem), left–right and angular anisotropy for 0.5 MeV neutrons, and the contribution of different mechanisms of neutron emission in fission. New additional experimental and theoretical efforts are urgently necessary. Some proposals are given in this chapter.