Decisive role of wriggling vibrations in the formation of angular and spin distributions of products originating from bi
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CLEI Theory
Decisive Role of Wriggling Vibrations in the Formation of Angular and Spin Distributions of Products Originating from Binary and Ternary Fission of Oriented Nuclei S. G. Kadmensky1)* , V. E. Bunakov2), and D. E. Lyubashevsky1) Received January 18, 2017
Abstract—It is shown that the multiplicities and angular and energy distributions of neutrons and photons evaporated from thermalized fragments originating from the spontaneous and low-energy induced fission of nuclei, the relative yields of ground and isomeric states of final fragments, and the features of delayed neutrons emitted upon the beta decay of the above fragments can successfully be described by employing nonequilibrium distributions of spins and relative orbital angular momenta of fission fragments formed in the vicinity of the scission point for the fissile nucleus being studied. It is also shown that these distributions, which are characterized by large mean values of the spins and orbital angular momenta directed orthogonally to the symmetry axis of the fissioning nucleus are successfully constructed upon simultaneously taking into account zero-mode transverse wriggling and bending vibrations of a fissile compound nucleus in the vicinity of its scission point, the wriggling vibrations being dominant. It is confirmed that the zero-mode wriggling vibrations considered immediately above are directly involved in the formation of the angular distributions of fragments originating from the spontaneous and low-energy fission of nuclei. This makes it possible to describe successfully such distributions for photofission fragments. DOI: 10.1134/S106377881705012X
1. INTRODUCTION Theoretical insights into the nature of experimental multiplicities and angular and energy distributions of neutrons [1, 2] and photons [3, 4] evaporated from thermalized fragments originating from the spontaneous and low-energy induced fission of actinide nuclei and into isomeric yield ratios for final fragments [3, 4], as well as into features of delayed neutrons emitted upon the beta decay of final fragments, rely on the assumption that the first and second fragments develop spins (total angular momenta) J1 and J2 that are large in relation to the fissioning-nucleus spin J, the spin vectors J1 and J2 being oriented orthogonally to the symmetry axis of the fissioning nucleus at the instant of its scission. Attempts at explaining this fact in terms of Coulomb interaction between strongly deformed fission fragments emitted from the fissioning nucleus proved to be unsatisfactory since the Coulomb interaction in question may change [5] the relative orbital angular momentum L and spins J1 and J2 of the fragments 1)
Voronezh State University, Universitetskaya pl. 1, Voronezh, 394036 Russia. 2) Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, Gatchina, Leningrad oblast, 188300 Russia. * E-mail: [email protected]
by the quantities ΔL, ΔJ1 , and ΔJ2 ≤ 2, respectively, which are substantially smaller than their mean values. At the present time, the origin of t
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