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1.
Since P-odd and T-odd asymmetries are generally not observed during the fissioning of unoriented target nuclei by polarized neutrons and oriented target nuclei by unpolarized neutrons, analogous asymmetries in angular distributions of products from binary and ternary fissioning of oriented target nuclei by cold polarized neutrons are thoroughly analyzed within the quantum theory of fission for finding these correlations. It is demonstrated that these correlations occur only when interference of the compound fissioning nucleus states with different spins is considered. Contributions from target nucleus orientations of different orders to coefficients of the asymmetries in question for fission fragments are estimated. Characteristics of analogous asymmetries for prescission and evaporation third particles are analyzed.  相似文献   

2.
Various interference effects governing the character of angular distributions of binary and ternary nuclear fission products and P-odd, P-even, and T-odd asymmetries in these angular distributions have been studied within the quantum theory of spontaneous and low-energy induced nuclear fission.  相似文献   

3.
Within the quantum-mechanical theory of the nuclear-fission process, the conditions of the emergence of coherent effects in the angular distributions of fragments originating from the binary and ternary fission of polarized nuclei are analyzed with allowance for the properties of transition fission states. In the case of ternary fission, the coefficients of P-odd asymmetry in the angular distributions of a light particle and a third particle, which is taken here to be an alpha particle, are calculated under the assumption that the third particle and two fragments are produced through a one-step mechanism. In order to confirm the ideas developed here, it is proposed to repeat, at a higher level of statistical accuracy, experiments devoted to seeking P-odd asymmetries for alpha particles in the ternary fission of nuclei.  相似文献   

4.
The experimentally measured P-odd, T-even; P-even, T-even; and P-even, T-odd asymmetries in the angular distributions of products of binary and ternary fission induced by cold polarized neutrons are classified, and the mechanisms of their appearance are studied. Basic asymmetries in the angular distributions of binary-fission fragments are found theoretically and are used to construct induced asymmetries in the angular distributions of prescission and evaporated third particles emitted in true and delayed ternary fission. If effects associated with the collective rotation of the polarized fissile system are disregarded, P-odd, T-even; P-even, T-even; and P-even, T-odd asymmetries in the angular distributions of prescission and evaporated photons are proven to be absent, and the coefficients of the analogous asymmetries in the angular distributions of prescission and evaporated neutrons are calculated for this case. The features of the coefficients of induced P-even, T-odd asymmetries are studied for evaporated photons and neutrons associated with taking into account the quantum rotation of the polarized fissile system.  相似文献   

5.
We consider the results of experimental measurements of P-odd and P-even (left-right) and T-odd asymmetries of charged-particle emission in binary and ternary fission induced by polarized neutrons. We show what information on the ternary-fission mechanism can be obtained from a theoretical analysis of these data.  相似文献   

6.
The problem of describing T-odd asymmetries in ternary fission reactions of oriented nuclei is solved for the first time on the basis of quantum theory. Estimates of the T-odd asymmetry coefficients in the angular distributions of the reaction products are obtained using the spin density matrix of the oriented fissioning nucleus. It is demonstrated that experiments on observing T-odd asymmetries in the spontaneous fission of oriented nuclei are of interest because the T-odd asymmetry coefficients can be around an order of magnitude greater than similar coefficients in the fission of unoriented target nuclei induced by polarized neutrons.  相似文献   

7.
The mechanisms and the features of the main types of nuclear ternary fission (that is, true ternary fission, in which a third particle is emitted before the rupture of the fissioning nucleus into fragments, and delayed ternary fission, in which a third particle is emitted from fission fragments going apart) are investigated within quantum-mechanical fission theory. The features of T-odd asymmetry in true ternary nuclear fission induced by cold polarized neutrons are investigated for the cases where alpha particles, prescission neutrons, and photons appear as third particles emitted by fissioning nuclei, the Coriolis interaction of the spin of the polarized fissioning nucleus with the spin of the third particle and the interference between the fission amplitudes for neutron resonances excited in the fissioning nucleus in the case of projectile-neutron capture being taken into account. For the cases where third particles emitted by fission fragments are evaporated neutrons or photons, T-odd asymmetries in delayed ternary nuclear fission induced by cold polarized neutrons are analyzed with allowance for the mechanism of pumping of large fission-fragment spins oriented orthogonally to the fragment-emission direction and with allowance for the interference between the fission amplitudes for neutron resonances.  相似文献   

8.
Within quantum-mechanical fission theory, P-odd and P-even correlations in angular distributions of products of the ternary fission of nuclei that is induced by polarized cold and thermal neutrons are investigated on the basis of a nonevaporative mechanism of third-particle emission and under the assumption that a two-humped fission barrier exists. It is shown that these correlations for third particles are induced by the analogous correlations for ternary-fission fragments, the latter being transferred to the third particle because of the kinematical conditions of third-particle emission that are associated with the charge and mass asymmetry of fragments. Optimum methods for observing the above correlations for third particles are discussed. The possibility of discovering the emission of prescission neutrons in the fission process against the background of evaporated neutrons by means of studying P-odd and P-even correlations is explored.  相似文献   

9.
P-odd asymmetries in binary fission of oriented target nuclei induced by cold polarized neutrons are described for the first time using methods of the quantum theory of fission. A spin matrix of the compound nucleus density is constructed with allowance for the interference of the fission amplitudes of various pairs of neutron resonances excited in the given nucleus during the capture of a cold polarized neutron by the oriented target nucleus. In the differential cross sections for this reaction we obtain not only P-odd T-even correlations with the angular dependence different from that of the earlier investigated correlations in the fission of unoriented target nuclei by polarized neutrons but also P-odd T-odd correlations that do not occur in the fission of unoriented target nuclei by polarized neutrons and oriented target nuclei by unpolarized neutrons.  相似文献   

10.
Some shortcomings of the approaches that are used to describe T-odd ROT and TRI asymmetries in true ternary fission via reactions involving the emission of prescission alpha particles and which are based on employing the classical method of trajectory calculations are analyzed. These shortcomings are caused by the disregard of the interference between the fission widths of different sJs neutron resonance states formed in the first well of the deformation potential of fissile compound nuclei. It is shown that the method used in some studies to determine T-odd TRI-asymmetries for prescission alpha particles is at odds with basic concepts of the generalizedmodel of the nucleus and approaches to constructing collective (for example, bending) vibrations of a fissile compound nucleus. Quantum-mechanical fission theory is generalized via employing a unified mechanism of formation of T-odd TRI and ROT asymmetries for prescission alpha particles and evaporated photons (neutrons). The proposed mechanism takes correctly into account the effect of quantum rotation of a fissile compound nucleus on the angular distributions of fission fragments and alpha particles for true ternary fission, as well as on the angular distribution of prompt photons (neutrons) emitted by fragments originating from the delayed fission of the aforementioned nuclei.  相似文献   

11.
We review the experimental results on the P-even and P-odd angular correlations of fission fragments in the fission of the 235U and 239Pu nuclei induced by unpolarized and polarized resonance neutrons, and on the TRI and ROT effects in the ternary and binary fission of actinides induced by polarized thermal neutrons. Also reported are the measured yields of prompt and delayed neutrons per fission event. The experimental data are analyzed within a novel theoretical framework developed by the JINR—RNC KI Collaboration, whereby the reduction of the multidimensional phase space of fission fragments to the JπK-channel space is consistently validated and the role of resonance interference in the observed correlation effects is revealed.  相似文献   

12.
Prospects for further studies of TRI and ROT effects of T-odd asymmetry in the emission of light particles in the ternary and binary fission of heavy nuclei that is induced by slow polarized neutrons are considered with a view to studying the mechanism for the formation of these effects and using them to get new information about fission dynamics. It is planned to investigate the dependence of the corresponding T-odd-asymmetry coefficients on the main characteristics of the fission reaction.  相似文献   

13.
Conditions for the appearance and observation of prescission γ-rays emitted by a fissioning nucleus before its separation into fission fragments were investigated within the quantum theory of fission. It was demonstrated that these conditions can be fulfilled in the γ-decay of giant electric isovector dipole resonances in a fissioning nucleus that become excited due to the nonadiabaticity of the collective deformation motion of the nucleus at the final stages of its prefission evolution. Angular and energy distributions of prescission γ-rays emitted by unpolarized fissioning nuclei were analyzed. Characteristics of T-odd asymmetries in angular distributions of prescission γ-rays were investigated for fission of unpolarized target nuclei induced by polarized cold neutrons, and these correlations were shown to be similar in nature to the T-odd ROT correlations earlier found for α-particles emitted in ternary nuclear fission.  相似文献   

14.
15.
The principal values for the even and odd components of the amplitudes of the angular distributions of α particles emitted as the third particles in true low-energy ternary fission of nuclei are calculated within the quantum theory of fission using natural approximations for the dependence of the potential scattering phases of the α particle on its orbital momenta and experimental angular distributions, unperturbed by the fissioning nucleus rotation, of these third α particles. Knowing the angular dependences of these components, we can estimate the angular dependences of the T-odd ROT and TRI asymmetry coefficients for the ternary fission of actinide nuclei induced by cold polarized neutrons.  相似文献   

16.
The coefficients of P-odd, P-even, and T -odd asymmetries for a third and a fourth prescission particle emitted in the true quaternary fission of nuclei that was induced by polarized cold neutrons were studied on the basis of quantum-mechanical fission theory. By using non-evaporation (nonadiabatic) mechanisms of light-particle emission, these coefficients were compared with the analogous coefficients for prescission third particles emitted in the ternary fission of nuclei.  相似文献   

17.
Differential cross sections for reactions of the true ternary fission of nuclei that was induced by cold polarized neutrons were constructed with allowance of the effect that Coriolis interaction and the interference between fission amplitudes of neutron resonances excited in fissile nuclei upon incidentneutron capture by target nuclei exerted on angular distributions of prescission third particles (alpha particles, neutrons, or photons). It is shown that T -odd TRI- and ROT-type asymmetries for prescission alpha particles are associated with, respectively, the odd and even components of the Coriolis interaction-perturbed amplitude of angular distributions of particles belonging to the types indicated above. These asymmetries have angular distributions differing from each other and stemming from a nontrivial dependence of these components on the neutron-resonance spins J s and their projections K s onto the symmetry axis of the nucleus involved. It is shown that angular distributions of prescission photons and neutrons from reactions of the ternary fission of nuclei that is induced by cold polarized neutrons are determined by the effect of Coriolis forces exclusively. Therefore, the emerging T-odd asymmetries have a character of a ROT-type asymmetry and are universal for all target nuclei.  相似文献   

18.
T-odd asymmetries in the ternary fission of oriented target nuclei, induced by cold unpolarized neutrons and accompanied by emission of ?? particles, are described using quantum fission theory. The differential cross section for the reaction in question is obtained using the spin density matrix of the target nucleus by considering the Coriolis interaction of the spin of a fissioning compound nucleus with the orbital momentum of an ?? particle and interference from the fission amplitudes of various pairs of neutron resonances excited in the compound nucleus as the target nucleus captures a cold neutron. It is shown that in the case under consideration, T-odd asymmetries occur only at odd values of the target nucleus??s order of orientation. It is demonstrated that the concepts of TRI and ROT asymmetries are preserved while the absolute values of the coefficients for these asymmetries can change noticeably in comparison to the similar coefficients for the fission of unoriented target nuclei induced by cold polarized neutrons.  相似文献   

19.
A version of a theoretical explanation is proposed for the recently discovered effect of T-odd correlation in ternary nuclear fission induced by polarized neutrons. It is shown that the inclusion of the Coriolis interaction between a third particle and the fissile-nucleus spin within the quantum theory of fission makes it possible to explain the experimental features of the effect and provides a correct estimate of its magnitude.  相似文献   

20.
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