Theoretical Analysis of Experimental Data on the Angular Anisotropy of Fragments of Nuclear Fission Induced by Neutrons
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retical Analysis of Experimental Data on the Angular Anisotropy of Fragments of Nuclear Fission Induced by Neutrons at Energies of up to 200 MeV A. L. Barabanova, b, *, A. S. Vorobyevc, A. M. Gagarskic, O. A. Shcherbakovc, and L. A. Vaishnenec a
National Research Center “Kurchatov Institute,” Moscow, 123182 Russia Institute of Physics and Technology, Dolgoprudny, Moscow oblast, 141701 Russia cKonstantinov Institute of Nuclear Physics, National Research Center “Kurchatov Institute,” Gatchina, Leningrad oblast, 188300 Russia *e-mail: [email protected] bMoscow
Received October 30, 2019; revised November 25, 2019; accepted December 27, 2019
Abstract—Problems of describing experimental data on the angular distributions of fragments of nuclear fission induced by intermediate-energy neutrons are discussed. A way of calculating angular distributions based on using the TALYS program is proposed. The capabilities of the technique for obtaining new information on the fission process and reactions at intermediate energies are shown by the example of describing data obtained for the 237 Np nucleus. DOI: 10.3103/S1062873820040036
INTRODUCTION In the fission of nuclei by fast neutrons with nonzero orbital momenta l, fragments are emitted anisotropically relative to the axis of collision. Like many other aspects of fission, this effect is due to transitional states of the nucleus at the barrier. The main results from initial studies of the angular anisotropy of fragments using neutrons with relatively low energies of up to 20 MeV were summarized in [1]. Results from measuring the angular anisotropy of fragments upon the fission of 232 Th and 238 U nuclei by neutrons with energies of up to 100 MeV were first presented in [2]. Systematic experimental studies of the angular distributions of fragments of nuclear fission induced by neutrons with intermediate energies of up to 200 MeV began only recently. In particular, we have obtained results for the nuclei of nat Pb, 209 Bi , 232 Th , 233 U , 235U , 238 U , 237 Np , and 239 Pu [3–8]. Similar measurements have also been made by the collaborations n-TOF for target nuclei of 232 Th [9], 235U , and 238 U [10], and NEFFTE for 235U [11]. In this work, we discuss the possibilities of theoretical description of the angular distributions of fragments of nuclear fission induced by neutrons. Intermediate energies are of particular interest, since there were no consistent theoretical approaches in this area until recently. We present our own model and results
of the first calculations for the reaction of 237 Np(n, f ) in a wide range of energies (up to 200 MeV). It is shown that improving the model and introducing additional parameters into it will allow us to use the results from measurements of the angular distributions of fragments to obtain new information on fission barriers, characteristics of nuclei at the barriers, the energies of transition states, and the role of pre-equilibrium processes in the interaction between nuclei and neutrons. FORMULATION OF THE PROBLEM The following co
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