Том 82, № 3 (2019)

The even—even rare-earth nuclei in U(5)—SU(3) region at neutron number (N) = 90, have been systematically studied using the Bohr—Mottelson Model (BM), Interacting Vector Boson Model (IVBM), and Interacting Boson Model (IBM). The positive ground-state band (GSB) of ¹⁵²Sm, ¹⁵⁴Gd, and ¹⁵⁶Dy nuclei has been calculated by using BM, IVBM, and IBM, while the negative-parity band (NPB) of those nuclei are calculated by BM and IVBM only. To determine the intermediate structure, the ratio (r(I + 2)/I) and E-GOS curve (E-Gamma Over Spin) as a function of the spin (I) have been drawn. In the IBM, the calculated reduced B(E2) transition probabilities of the GSB in the ¹⁵²Sm, ¹⁵⁴Gd, and ¹⁵⁶Dy nuclei are analyzed and compared to the prediction of vibrational U(5) and rotational SU(3) limits. In the Sm—Dy nuclei with N = 90, the U(5)—SU(3) IBM potential energy surfaces (PES’s) are analyzed and evolve from spherical to deformed shapes with increasing the boson number. The critical phase transition points are identified in the space of model parameters and ¹⁵²Sm,¹⁵⁴Gd, and ¹⁵⁶Dy nuclei have been found to be close to critical points.

Reactions involving loosely bound nuclei have many special features. An enhancement of interaction cross sections in the subbarrier energy region is one of them. This effect is pronounced for nuclei that have a cluster structure. Transfer and complete-fusion reactions are dominant interaction channels for them. Experimental data on the cross sections for fusion reactions induced by such nuclei deviate strongly from the predictions of the statistical compound-nucleus model at energies in the vicinity of the Coulomb barrier. Also, the cross sections for neutron transfer from ^3,6,8He and deuteron transfer from ^6,9Li were found to grow at deep subbarrier energies. These results are discussed from the point of view of the effect of the cluster structure of nuclei on the probability for their interaction at energies in the vicinity of the Coulomb barrier. A theoretical analysis of relevant experimental data was performed with allowance for the effect of outer neutrons and clusters in loosely bound nuclei of bombarding particles. The results of the present study may be used to solve some problems of astrophysics—in particular, to obtain deeper insight into the mechanism of the production of light elements in the Universe.

The energy spectra of μX rays for molybdenum and ruthenium targets were measured by means of high-purity germanium (HPGe) detectors in a muon beam at the Research Center for Nuclear Problems (RCNP, Osaka, Japan). The results of these measurements were included in the electronic atlas of mesoroentgen spectra. This information is necessary for identification of gamma lines, calibrating detectors, correctly choosing structural materials, and investigation the composition of matter.

A detailed analysis of T-odd asymmetries in the reactions of true ternary fission of nuclei that involves the emission of prescission alpha particles is performed within quantum-mechanical fission theory. This analysis is based on taking into account the effect of quantum rotation of a fissile compound nucleus formed upon the capture of a polarized cold neutron by an nonoriented target nucleus on angular distributions of both alpha particles and fission fragments. It is shown that the asymmetries in question cannot be described within the approach relying on the use of the classic method of trajectory calculations without taking into account the interference between the fission amplitudes for different neutron resonance states of a fissile compound nucleus that are formed at the initial stage of the reactions being studied.

for nuclear reactions that are two-body ones in the initial and final channels and which involve polarized particles, the T-null theorem stating the absence of vanishing observables in such reactions was proven in a number of studies by means of concepts of reaction \({\cal T}\) matrices that take into account general conservation laws along with T-invariance conditions in the “dynamically independent” approach. Not only does this approach focus on known mechanisms of such reactions, but it may also be applicable to their as-yet unknown mechanisms. By employing T-invariance conditions, the selection rules for specific mechanisms that make it possible to describe observables of a → b many-particle multistep nuclear reactions involving polarized particles are analyzed in the present study. It is shown that, in the differential cross sections for the initial nuclear reactions a → b and for \(\overline b \to \overline a \) reactions that are time-reversed with respect to them, the components characterized by specific P and T parities and related by T-invariance conditions are associated with unified mechanisms of their appearance and can be expressed in terms of unified scalar functions differing for a → b and \(\overline b \to \overline a \) reactions by the interchange of the channels and by the sign reversal for the momenta and spins of particles involved in these reactions. First, this permits selecting only one mechanism among all possible T-invariant mechanisms that describes simultaneously the features of the components considered for a → b and \(\overline b \to \overline a \) reactions and discarding all of the remaining mechanisms. Second, this enables one to obtain, in a number of cases, zero values for some components of the differential cross sections for the reactions in question. The latter constrains the applicability region of the aforementioned T-null theorem and makes it possible to use these components in the cross section for the initial reaction a → b to study the nature of T-noninvariant interactions.

Double differential yield of π^±, K^±, protons, and antiprotons as a function of laboratory momentum is presented using hadron production models. This study is done in several polar angle intervals from 0 < θ < 420 mrad for π^± mesons and 0 < θ < 360 mrad for K^± mesons, protons, and antiprotons. The study is carried out for p + C interactions at 120 GeV/c. For simulation, three hadron-production models: EPOS-LHC, EPOS 1.99, and QGSJETII-04 are used. Since no experimental data at 120 GeV/c is available yet, therefore, the models’ predictions are compared with the measurements of NA61/SHINE experiments at 31 GeV/c. It is found that the QGSJETII-04 model gives high peak value, for π^± mesons, in the polar angle interval of 20–40 mrad, while in the range of 40–240 mrad, EPOS-LHC shows higher yield than EPOS 1.99 and QGSJETII-04 models, whereas all show higher yield than the experimental data. For π^± mesons, in all angular intervals, at high momentum values, all the three models are consistent and surprisingly give the same yield as that of the experimental data. For K^± mesons, QGSJETII-04 shows higher peak values at all polar angles ranging from 0 to 360 mrad as compared to that of EPOS 1.99 and EPOS-LHC models, whereas all models give higher yield at low angular intervals than the experimental data and the same yield at high angular intervals. The models demonstrate similar yields for protons at all angles but underestimate the experimental data at low angular intervals and provide the same yield at high angular intervals. The QGSJETII-04 model presents higher yields of antiprotons in comparison to the EPOS 1.99 and EPOS-LHC models, for almost all angular intervals. Generally, at higher angular range, i.e., from 240 to 420 mrad, particularly at high momentum, all the three models show similar results.