Experimental and computed spectra of neutrons and photons emitted from spherical iron models with a 252Cf source at the center

Abstract

Series of experiments and calculations in which the spectra of neutrons and photons emitted from 20, 40, 50, 60, 70, and 100 cm in diameter spherical models with a 252 Cf source at the center are studied are described. The neutron spectra are measured with spectrometers based on stilbene and a hydrogen counter and the photon spectra are measured with spectrometers based on stilbene and a Si(Li) detector. The calculations are performed using the ROZ-6 computer program and the BNAB-78 28-group neutron constants library. The experimental fluxes of >0.8 MeV neutrons are, for the most part, greater than the computed values, and the fluxes of >0.35 MeV photons are also greater than the computed values. The differences reach a factor of 2-3. The data obtained show that the the cross sections for elastic and inelastic neutron scattering and radiative capture of neutrons need to be changed, leaving the total cross sections for the interaction of neutrons with iron in the constants library tested unchanged.There are two basic reasons why it is important to study the transfer of neutron and photon radiation in iron: the existence of discrepancies between the computed and experimental neutron and photon spectra from iron spherical models with a neutron source at the center [1-4] and the need to guarantee radiation resistance and longevity of the structural materials in a nuclear power system, first and foremost, VVÉR vessels. The discrepancies were found back in the beginning of the 1980s, when benchmark experiments were started for structural materials in nuclear systems and shielding materials. Over the next 20 years experiments were performed using different instruments and calculations were performed using different programs and constants libraries, but the problem of neutron and photon radiation transfer in iron cannot be considered as solved.Among all experimental studies of the transfer of ionizing radiation, benchmark experiments in a one-dimensional spherical geometry are of greatest value because in this case ideal conditions are created for testing the constants used in the calculations. A great deal of experience in performing experiments of this type and analyzing them computationally has been accumulated at the Physics and Power Engineering Institute. In the last few years a series of experiments and calculations where the neutron and photon spectra from spherical iron models with a 252 Cf source at the center have been performed [1,2,4]. In the new series of experiments, the accuracy of neutron and photon spectra from 20, 40, 50, 60, and 70 cm in diameter spherical models with a 252 Cf source at the center has been improved, the neutron and photon spectra from a 100 cm in diameter sphere have been investigated, and the spectra of monoenergetic photons accompany inelastic scattering of neutrons have been measured. In addition, calculations have been performed using the modern constants libraries.