Possible parity-violating effects in ternary fission

Possible parity-violating effects are considered in ternary fission and estimated for different assumptions regarding the mechanism of the process. Here we shall consider differentP-violating effects in neutron-induced ternary fission. As shown in [1], all theP-violating effects in nuclear reactions proceeding via the compound-nucleus stage bear some features in common. All of them are characterized by the factors of dynamical enhancement (caused by the large density of compound-nucleus states), resonance enhancement defined by the ratio of the level spacing for the states of opposite of opposite parity to the width these states [1], and structural enhancement (or hindrance) factors in the exit or entrance channels. Since we believe that neutron-induced ternary fission proceeds via the compound-nucleus stage, one can apply here the basic methods and results [1] used for binary fission, with some modifications necessitated by the presence of 3 particles in the exit channel. Since, however, the analytic analysis of the 3-body problem is rather abstruse and difficult even in classical mechanics, we shall use some reasonable hypothesis about the mechanism of ternary fission in order to obtain the order of magnitude estimates forP-violating effects.     

Effect of excessive pressure on the drift mobility of charge carriers in poly(diphenylene phthalide) films

The electron-hole transport in poly(diphenylene phthalide) films has been investigated. The dependence of the drift mobility of charge carriers on the excessive mechanical pressure has been studied using the time-of-flight method. It has been revealed that, with an increase in the thickness of the polymer film, the dispersive transport of charge carries gives way to the quasi-dispersive transport. In thin films in the prethreshold range (i.e., before switching of the samples to the highly conductive state under excessive pressure), the electron mobility increases and exceeds the hole mobility. The experimental results have been discussed in the framework of the model describing the transport through the channels formed by metastable electron-hole pairs.     

Purely quantum effects in fission

It is shown that the large values of the orbital momenta of relative motion of fission fragments result from purely quantum effects of orientational pumping related to the uncertainty relations.     

Recent developments in the theory of stripping to unbound states

A comparative analysis is carried out of different approaches to the calculation of DWBA cross sections for stripping to unbound states including single-particle resonances, compound resonances and the smooth background. A relationship is derived between unbound stripping and scattering cross sections on the same target. The reliability of spectroscopic factor concepts is discussed. Numerical checks are performed with the aid of stripping form factors obtained from the solution of a coupled channels equation system.     

Direct mechanisms of fast light particle formation in heavy ion collisions

Two direct mechanisms are considered for the heavy ion collisions which lead to fast α-particle emission: α-particle knock on by the incident ion and heavy fragment stripping of this ion. It is demonstrated that stripping mechanism allows to reproduce all the experimental characteristic features of the process except the cross-section dependence on α-particle separation energy in the target. Knock on process reproduces this feature as well. It is pointed that the analysis of experimental data on the hard part of α-particle spectrum allows to gain a unique information on the properties of the strongly rotating nuclei produced in these reactions.     

Parity non-conservation effects in neutron elastic scattering reactions

Energy dependence of parity non-conservation effects is derived for neutron elastic scattering on nuclei: emission asymmetry and the rotation of the polarization plane for the polarized neutron beam and longitudinal polarization for unpolarized neutrons. Both potential scattering and scattering through the compound-nucleus resonances (multi-level approximation) are taken into account. The expressions obtained are compared with experimental data on thermal neutron scattering.     

<Emphasis Type="Italic">T</Emphasis>-odd asymmetries for evaporation γ-rays in nuclear fission

T-odd asymmetries in angular distributions of evaporation γ-rays emitted by thermalized fragments resulting from the fission of axially symmetric deformed nuclei induced by cold polarized neutrons are investigated within the quantum theory of fission. The asymmetries in question are due to the anisotropy of the angular distributions of evaporation γ-rays, caused by zero wriggling vibrations of the fissioning nucleus and associated with the orientation of large fission fragment spins in the direction perpendicular to the direction n ₀ of the symmetry axis of the fissioning nucleus at the time of its separation into fragments. The angle of rotation of the vector n ₀ with respect to the asymptotic direction of the light fission fragment emission is calculated with allowance for the interference of fission amplitudes of neutron resonances excited in the fissioning nucleus as it captures the incident neutron. It is shown that the angular and energy characteristics of the T-odd asymmetry calculated for evaporation γ-rays agree with the characteristics of the experimentally investigated T-odd asymmetry in angular distributions of all γ-rays emitted by a fissioning ²³⁶U nucleus.     

Transition fission states for heated nuclei

Induced fission reactions of fissioning compound nuclei that result from the capture of various incident particles (nucleons, γ rays, multiply charged ions) by target nuclei are investigated using the generalized nucleus model and the Wigner random matrix method. The effect produced on the fission widths of the compound nucleus by the competition between the excitation energies of its collective vibrational degrees of freedom that lead to its scission into fission fragments and its rotational and multi-quasiparticle states is analyzed. Bohr’s concept of transition fission states developed for near-barrier nuclear fission is generalized to the induced fission of nuclei with the excitation energies noticeably higher than the fission barriers. The temperature of the fissioning nucleus in the vicinity of the point of its scission into fission fragments is estimated.