Role of dynamical effects in the formation of T -Odd asymmetries for products of polarized-neutron-induced ternary fissi
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CLEI Theory
Role of Dynamical Effects in the Formation of T -Odd Asymmetries for Products of Polarized-Neutron-Induced Ternary Fission of Nuclei S. G. Kadmensky1)* , V. E. Bunakov2), and L. V. Titova1) Received January 19, 2015
Abstract—Basic dynamical effects that accompany the cold-polarized-neutron-induced binary and ternary fission of actinide nuclei and which determine the properties of T -odd asymmetries in angular distributions of various prescission and evaporated light third particles emitted in true and delayed ternary fission are analyzed on the basis of quantum-mechanical fission theory. It is emphasized that effects associated with the conservation of axial symmetry of the fissioning system under study at all stages of its evolution from the formation of neutron resonance states of the fissile compound nucleus to the separation of its fission fragments, including the appearance of zero wriggling vibrations of the cold compound nucleus in the vicinity of its scission point, are of particular importance, the influence of quantum collective rotation of the polarized fissile system on the asymmetry of the angular distribution of both fission fragments and third particles being taken into account. It is shown that the difference in the behavior of the coefficients characterizing the T -odd asymmetries under analysis for the target nuclei being studied can be explained, upon taking into account the interference between the fission amplitudes for the neutron resonance states of fissile compound nuclei, by the difference in the contributions of even and odd components of the amplitudes of angular distributions of third particles to the coefficients in question. DOI: 10.1134/S1063778815050105
1. INTRODUCTION The experiments reported in [1–5] were devoted to studying T -odd asymmetries in the differential cross sections dσn,f /dΩ3 for the reactions in which the true ternary fission of 233 U, 235 U, and 239 Pu target nuclei was induced by cold polarized neutrons. Here, Ω3 is the solid angle that determines the direction of the asymptotic momentum p3 for a third particle, which was an alpha particle in those experiments [1–5]. The differential cross sections dσn,f /dΩ3 were analyzed in the laboratory frame where the z and y axes were aligned with, respectively, the asymptotic momentum of the light fission fragment, pLF , and the polarization vector of the incident neutron, sn . A coefficient that was intended for characterizing the T -odd asymmetries under analysis, D (Ω3 ), was chosen in the form ⎛ =⎝ 1)
D (Ω3 ) ⎞⎛
(+)
dσn,f dΩ3
(−)
−
dσn,f dΩ3
⎠
⎝
(+)
dσn,f dΩ3
(−)
+
dσn,f dΩ3
⎞
(1)
⎠,
Voronezh State University, Universitetskaya pl. 1, Voronezh, 394036 Russia. 2) Petersburg Nuclear Physics Institute, National Research Center Kurchatov Institute, Gatchina, 188300 Russia. * E-mail: [email protected]
where the signs (±) corresponded to two opposite directions of the neutron polarization vector sn . Figures 1–3 show that the experimental T -oddasymmetry coefficients D exp (Ω3 ) from [1–5] differ substantially in shape fo
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