Mechanisms of excitation of T -odd correlations for prescission gamma rays and structure of these correlations
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CLEI Theory
Mechanisms of Excitation of T -Odd Correlations for Prescission Gamma Rays and Structure of These Correlations V. E. Bunakov1), S. G. Kadmensky2)* , and S. S. Kadmensky2) Received December 5, 2008
Abstract—Conditions for the appearance and observation of prescission gamma rays emitted by a fissioning nucleus prior to its separation into fission fragments were investigated within quantum-mechanical fission theory. It is shown that these conditions are realizable in the gamma decay of isovector electric giant dipole resonances in a fissile nucleus that are excited because of nonadiabaticity of the collective deformation motion of the nucleus at the ultimate stages of its prefission evolution. Angular and energy distributions of prescission gamma rays emitted by unpolarized fissioning nuclei are analyzed. Features of T -odd correlations in angular distributions of gamma rays arising in the fission of unpolarized target nuclei that is induced by polarized cold neutrons are investigated, and it is shown that these correlations are similar in nature to T -odd ROT correlations discovered earlier for alpha particles emitted in the ternary fission of nuclei. PACS numbers: 25.85.-w, 25.85.Ec DOI: 10.1134/S1063778809080109
1. INTRODUCTION The question of whether prescission gamma rays emitted from a fissioning nucleus prior to its separation into fission fragments can be observed experimentally against the background of well-studied and much more probable evaporation gamma rays emitted by thermalized fission fragments at the stage following the emission of evaporated neutrons from these fragments is one of the interesting as-yet-unresolved problems in contemporary fission physics. The appearance of prescission gamma rays may be associated with a rather fast gamma decay of excited states of a fissile nucleus that are generated by the nonadiabaticity of the collective deformation motion of this nucleus at stages preceding its separation into fission fragments. Therefore, angular and energy distributions of prescission gamma rays must differ substantially from the analogous distributions for evaporation gamma rays. The present study is devoted to exploring, within quantum-mechanical fission theory [1–4], mechanisms of the excitation of prescission gamma rays and conditions under which their observation is possible. Particular attention will be given to analyzing the structure of T -odd correlations in angular distributions of prescission gamma 1)
Petersburg Nuclear Physics Institute, Russian Academy of Sciences, Gatchina, 188300 Russia. 2) Voronezh State University, Universitetskaya pl. 1, Voronezh, 394006 Russia. * E-mail: [email protected]
rays emitted in the fission of unpolarized nuclei that is induced by polarized cold neutrons. The appearance of such correlations, along with characteristic angular and energy distributions, may serve as a proof of the existence of prescission gamma rays. In recent years, experimental and theoretical searches for prescission gamma rays have been motivated to a considerable extent by the di
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