Experimental determination and computational modeling of threshold reaction rates in 0.8 GeV proton-irradiated lead target

Abstract

The results of an experimental determination and computational modeling of the rates of threshold reactions on 209 the external surface of and inside a thick lead target irradiated by 0.8 GeV protons are presented. The reaction rates were measured by γ spectrometry using Ge and (Ge-Li) detectors with resolution 1.8 and 2.9 keV, respectively, on the 1332 keV γ-line. Measurements of 2467 independent and cumulative threshold reaction rates were performed with 244 samples. The LAHET program was used for computational modeling of the results. The MENDL and MENDL2p libraries, the EXFOR databases, and the LAHET program were used to construct the excitation functions of the nuclides formed. The experimentally measured reaction rates are compared with the computed rates. The neutron and proton fluxes along the target, both on its external surface and in the interior volume, were calculated using the experimental threshold reaction rates and the computed cross sections of the reactions averaged over the spectrum of the neutrons and protons. The reaction rates measured inside and on the surface of a natural-lead target were used to determine the accuracy with which the target's activity is measured.Two types of facilities are now being designed and built on the basis of high-current accelerators. The first type consists of neutron sources which can be used successfully in fundamental and applied physics, materials science, and biology; the second type consists of electronuclear facilities for transmutation of radioactive wastes and, possibly, the production of electricity. Even though there are structural differences, which are due to the purpose of a facility, the two types have a unit in common -a target which is bombarded by a proton beam from a high-current linear accelerator. Ordinarily, a Pb + Bi eutectic, Pb, Hg (liquid targets), or W, Ta (solid targets) are used as target materials.The presence of a target unit, which is used to generate neutrons of a hadron-nuclear cascade, in nuclear facilities raises the problem of determining its basic neutron-physical parameters. Individual parameters directly affect the nuclear-physical characteristics of the blanket (the total yield and spectrum of neutrons from the target); other parameters affect the nuclear-physical characteristics of the target itself (energy release, radiation resistance, production of residual prod-