Cross sections and barriers for nuclear fission induced by high-energy nucleons
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CLEI Theory
Cross Sections and Barriers for Nuclear Fission Induced by High-Energy Nucleons O. T. Grudzevich1)* and S. G. Yavshits2) Received November 30, 2011; in final form, June 22, 2012
Abstract—The cross sections for the fission of 232 Th, 235,238 U, 237 Np, and 239 Pu target nuclei that was induced by 20- to 1000-МeV neutrons and protons were calculated. The respective calculations were based on the multiconfiguration-fission (MCFx) model, which was used to describe three basic stages of the interaction of high-energy nucleons with nuclei: direct processes (intranuclear cascade), equilibration of the emerging compound system, and the decay of the compound nucleus (statistical model). Fission barriers were calculated within the microscopic approach for isotopic chains formed by 15 to 20 nuclei of the required elements. The calculated fission cross sections were compared with available experimental data. It was shown that the input data set and the theoretical model used made it possible to predict satisfactorily cross section for nuclear fission induced by 20- to 1000-МeV nucleons. DOI: 10.1134/S1063778813010055
INTRODUCTION The model of multiconfiguration fission [1] was constructed as a development of the traditional approach to describing nuclear reactions: the intranuclear-cascade model [2], the exciton model of preequilibrium decay [3], and the statistical model of nuclear reactions [4]. The models developed in [2– 4] were substantially modified in such a way as to attain a reasonable description of experimental data on the features of emitted particles by using a single set of parameters. For example, the exciton model of preequilibrium decay was extended by introducing in it the possibility of calculating multiparticle emission without increasing the number of parameters, and the instant of statistical equilibration in the compound system was validated within this model on the basis of physical consideration [5]. Within the intranuclearcascade model, the instant of cascade interruption was studied in detail, and the energy-barrier parameters, which take the place of the threshold cutoffenergy value used earlier [6], were selected on the basis of an analysis of neutron spectra. Within the statistical model of nuclear reactions, the method for calculating radiative strength functions was modified substantially: the temperature dependence of radiative strength functions was proposed and was tested on the basis of a vast body of experimental 1)
Leipunsky Institute for Physics and Power Engineering, pl. Bondarenko 1, Obninsk, Kaluga oblast, 249033 Russia. 2) Khlopin Radium Institute, 2nd Murinsky pr. 28, St. Petersburg, 194021 Russia. * E-mail: [email protected]
data [7]. The entrance reaction channel was described by means of the coupled-reaction-channel method as implemented within the ECIS code [8] by using a global optical potential developed for target nuclei in the range from lead to plutonium and for nucleon energies in the range extending up to 1 GeV [9]. In Fig. 1, the results of the calculations are cont
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