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Title: Sequential character of low-energy ternary and quaternary nuclear fission

Abstract

An analysis of low-energy true ternary (quaternary) nuclear fission leads to the conclusion that these fission modes have a sequential two-step (three-step) character such that the emission of a third particle (third and fourth particles) and the separation of fission fragments occur at distinctly different instants, in contrast to the simultaneous emergence of all fission products in the case of onestep ternary (quaternary) fission. This conclusion relies on the following arguments. First, the emission of a third particle (third and fourth particles) from a fissile nucleus is due to a nonevaporative mechanism associated with a nonadiabatic character of the collective deformation motion of this nucleus at the stages preceding its scission. Second, the axial symmetry of the deformed fissile compound nucleus and the direction of its symmetry axis both remain unchanged at all stages of ternary (quaternary) fission. This circumstancemakes it possible to explain themechanism of the appearance of observed anisotropies and T — odd asymmeries in the angular distributions of products of ternary (quaternary) nuclear fission. Third, the T —odd asymmetry discovered experimentally in ternary nuclear fission induced by cold polarized neutrons obeys the T —invariance condition only in the case of a sequential two-step (three-step) character of truemore » ternary (quaternary) nuclear fission. At the same time, this asymmetry is not a T —invariant quantity in the case of the simultaneous emission of products of true ternary (quaternary) nuclear fission from the fissile compound nucleus.« less

Authors:
;  [1]
  1. Voronezh State University (Russian Federation)
Publication Date:
OSTI Identifier:
22612611
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Atomic Nuclei; Journal Volume: 79; Journal Issue: 5; Other Information: Copyright (c) 2016 Pleiades Publishing, Ltd.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 74 ATOMIC AND MOLECULAR PHYSICS; ANGULAR DISTRIBUTION; ANISOTROPY; ASYMMETRY; AXIAL SYMMETRY; COMPOUND NUCLEI; EMISSION; FISSION FRAGMENTS; FISSION PRODUCTS; NEUTRONS; NUCLEAR DEFORMATION; QUATERNARY FISSION; T INVARIANCE; TERNARY FISSION

Citation Formats

Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru, and Bulychev, A. O. Sequential character of low-energy ternary and quaternary nuclear fission. United States: N. p., 2016. Web. doi:10.1134/S1063778816050112.
Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru, & Bulychev, A. O. Sequential character of low-energy ternary and quaternary nuclear fission. United States. doi:10.1134/S1063778816050112.
Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru, and Bulychev, A. O. 2016. "Sequential character of low-energy ternary and quaternary nuclear fission". United States. doi:10.1134/S1063778816050112.
@article{osti_22612611,
title = {Sequential character of low-energy ternary and quaternary nuclear fission},
author = {Kadmensky, S. G., E-mail: kadmensky@phys.vsu.ru and Bulychev, A. O.},
abstractNote = {An analysis of low-energy true ternary (quaternary) nuclear fission leads to the conclusion that these fission modes have a sequential two-step (three-step) character such that the emission of a third particle (third and fourth particles) and the separation of fission fragments occur at distinctly different instants, in contrast to the simultaneous emergence of all fission products in the case of onestep ternary (quaternary) fission. This conclusion relies on the following arguments. First, the emission of a third particle (third and fourth particles) from a fissile nucleus is due to a nonevaporative mechanism associated with a nonadiabatic character of the collective deformation motion of this nucleus at the stages preceding its scission. Second, the axial symmetry of the deformed fissile compound nucleus and the direction of its symmetry axis both remain unchanged at all stages of ternary (quaternary) fission. This circumstancemakes it possible to explain themechanism of the appearance of observed anisotropies and T — odd asymmeries in the angular distributions of products of ternary (quaternary) nuclear fission. Third, the T —odd asymmetry discovered experimentally in ternary nuclear fission induced by cold polarized neutrons obeys the T —invariance condition only in the case of a sequential two-step (three-step) character of true ternary (quaternary) nuclear fission. At the same time, this asymmetry is not a T —invariant quantity in the case of the simultaneous emission of products of true ternary (quaternary) nuclear fission from the fissile compound nucleus.},
doi = {10.1134/S1063778816050112},
journal = {Physics of Atomic Nuclei},
number = 5,
volume = 79,
place = {United States},
year = 2016,
month = 9
}
  • An analysis of basicmechanisms of binary and ternary fission of nuclei led to the conclusion that true ternary and quaternary fission of nuclei has a sequential two-step (three-step) character, where, at the first step, a fissile nucleus emits a third light particle (third and fourth light particles) under shakeup effects associated with a nonadiabatic character of its collective deformation motion, whereupon the residual nucleus undergoes fission to two fission fragments. Owing to this, the formulas derived earlier for the widths with respect to sequential two- and three-step decays of nuclei in constructing the theory of two-step twoproton decays and multistepmore » decays in chains of genetically related nuclei could be used to describe the relative yields and angular and energy distributions of third and fourth light particles emitted in (α, α), (t, t), and (α, t) pairs upon the true quaternary spontaneous fission of {sup 252}Cf and thermal-neutron-induced fission of {sup 235}U and {sup 233}U target nuclei. Mechanisms that explain a sharp decrease in the yield of particles appearing second in time and entering into the composition of light-particle pairs that originate from true quaternary fission of nuclei in relation to the yields of analogous particles in true ternary fission of nuclei are proposed.« less
  • On the basis of quantum-mechanical fission theory, the features of true quaternary nuclear fission are studied by treating this fission process as a sequence of three processes following one another in the course of time. The first two processes are the escape of the first and then the second of the two light particles emitted from the neck of a fissioning nucleus because of a nonadiabatic character of the collective deformation motion of this nucleus. Finally, the third process is the separation of the fissioning nucleus into two rather heavy fission fragments. The differences that arise in the emission probabilitiesmore » and in the angular and energy distributions upon going over from the first emitted to the second emitted prescission third and fourth particles are analyzed by invoking experimental data on the spontaneous and thermalneutron-induced fission of nuclei, and it is shown that these differences are caused by the changes both in the geometric configuration of the fissioning nucleus and in the shell structure of its neck after the first prescission particle is emitted from it.« less
  • Groups of alpha particles having average energies of 10.6, were counted by using different thicknesses of aluminum foil. The relative number of ternary fission events to binary fission events is tabulated for the four groups of alpha particle energies. The energies of the fission fragments from ternary fission were measured by a multi-channel amplitude analyzer. The total decreases in energy of the light and heavy fission fragments DELTA E/sub l/ and DELTA E/ sub h/ are tabulated for the four groups of alpha -particle energies. The total decrease in energy of the fission fragments ( DELTA E/sub t/) is 10.9more » Mev for an average E/sub alpha / of 10.6 Mev. 15.0 Mev for an E/sub alpha / of 18.4 Mev, 14.S Mev for an E/sub alpha / of 20.3 Mev, and 15.5 plus or minus 1.6 Mev for an E/sub alpha / of 24.0 Mev. The results show that the total kinetic energy during ternary fission increases with increasing energy of the long-range alpha particle and can significantiy exceed the total kinetic energy of binary fission. The mass ratio of the fission fragments (M/sub 2/M/sub 1/) remains constant at 1.5 for various energies of the long-range alpha particles. (TTT)« less