Том 81, № 6 (2017)

The level structure of lithium isotope ⁶Li is studied in the reaction of the absorption of stopped pions ¹²С(π⁻, tt)X. States are sought up to excitation energies of ~40 MeV in the missing mass spectrum. Data on highly excited states are analyzed to determine their origins. The final results are compared to those from searches for the highly excited states of heavier lithium isotopes produced in the reaction of the absorption of stopped pions.

New data on the energy dependence of integral cross sections of the ⁷Li(p, α)⁴He reaction are obtained to develop the SaBa (Sarov Base) library of evaluated and experimental nuclear data at the Russian Federal Nuclear Center, All-Russia Research Institute of Experimental Physics [1]. The sum of smooth and resonance parts is used as an approximating function in the current version of the SaBa database. The smooth part is described by cubic splines. Lorentzians are used to describe resonance regions. Experimental data already available in the SaBa library are analyzed to obtain new evaluated data on the ⁷Li(p, α)⁴He reaction, and a search is conducted for new data in domestic and foreign literary sources.

Using objective physical criteria for data reliability, cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n) and (γ, 3n) that are free of the shortcomings of neutron multiplicity sorting methods used on beams of quasimonoenergetic annihilation photons are obtained for ¹⁴¹Pr and ¹⁸⁶W nuclei. Evaluation is performed using the experimental–theoretical method (ETM), based on the experimental cross section of neutron yield reaction σ^exp(γ, xn) = σ^exp(γ, 1n) + 2 σ^exp(γ, 2ⁿ) + 3 σexp(γ, 3n) + … and ratios F_i^theor= σ^theor(γ, in)/σ^theor(γ, xn) calculated within the combined model (CM) of photonuclear reactions, which stipulates that σ^eval(γ, in) = F_i^theor σ^exp(γ, xn). It is found that for ¹⁴¹Pr and ¹⁸⁶W, ratios F^exp_i do not contradict the data reliability criteria only at energies up to ~21 and ~22 MeV, respectively. At the same time, there are notable discrepancies between F_i^theor and F^exp_i, and thus between the evaluated and experimental cross sections of reactions. It is shown that the discrepancies between the evaluated and experimental cross sections are due to the assumed unreliable experimental distribution of neutrons in the channels with multiplicities 1, 2, and 3.

The differential cross section of the elastic scattering of π^±-mesons by the ⁹Ве nucleus at energies of 0.6 and 1.0 GeV are calculated using the Glauber theory of multiple scattering. The wave function of the ⁹Ве nucleus is obtained in the three-cluster 2α-n model. The sensitivity of the differential cross sections to the wave functions of a target nucleus, calculated with different intercluster interaction potentials, and to the contribution from different orders of scattering in Glauber operator Ω is studied.

The neutron dispersive optical potential for Ag isotopes is constructed for a wide range of variation in the N number. Good agreement with the experimental data on the scattering of neutrons by ¹⁰⁷Аg isotopes, and on single-particle energies and the probabilities of subshell occupation near the Fermi energy, is obtained for stable isotopes ^{107, 109}Ag using the dispersive optical model. Calculations that predict the evolution of the neutron single-particle energies up to the boundary of neutron stability are performed. It is shown that new magic number N = 56 (for Z = 40) disappears upon moving from Zr to Sn in an isotonic chain with N = 56, due to rapid deepening of level 1g_7/2.

Experimental cross sections of formation of isotopes ⁴⁶Sc (in reaction ⁶He + ⁴⁵Sc), ^196,198Au (in reaction ⁶He + ¹⁹⁷Au), and ⁶⁵Zn (in reaction ⁶He + ⁶⁴Zn) are analyzed. The time-dependent Schrödinger equation for the outer neutrons of ⁶He and ¹⁹⁷Au nuclei is solved numerically to calculate the probability of neutron transfer and transfer cross sections. In reaction ⁶He + ¹⁹⁷Au, the contribution of fusion and subsequent evaporation to experimental data can be neglected, while the corresponding contributions to reactions ⁶He + ⁴⁵Sc and ⁶He + ⁶⁴Zn are considerable. Fusion–evaporation is taken into account using the computational code of the NRV knowledge base. The results of calculations are in satisfactory agreement with the experimental data.

A way of calculating the average spins of induced fission fragments is developed, based on the dynamic model of their angular distributions. The range of relaxation times for the degree of freedom associated with the orientation of the axis of symmetry of a fissioning nucleus relative to its total angular momentum is determined by analyzing experimental data on the energy dependences of average spins and the anisotropy of the angular distributions of fission fragments for the ¹²C, ¹⁶O + ²³²Th reactions at E_сm = 55–150 MeV.

The cross section of inelastic neutrino interaction with ⁵⁶Fe and ²⁰⁸Pb nuclei is calculated. Investigation of these processes caused by neutral currents is essential for considering phenomena that occur during Supernova explosions and designing astrophysical neutrino detectors. The inelastic neutrino scattering cross section is calculated using the model independent approach, which is based on experimental data on nuclear structure. The values of the matrix elements of the considered reaction are determined from the characteristics of electromagnetic dipole М1 transitions in nuclei, obtained by means of nuclear resonance fluorescence.

The Department of Accelerator Physics and Radiation Medicine of Moscow State University’s Faculty of Physics conducts experiments on the radiation processing of food products and the development of a new technology for the combined sterilization of bone implants, based on the joint action of different sterilizing factors (radiation and sterilization) in a gaseous medium. Radiation processing of potato tubers and bone implants is performed using accelerated electron beams with energies of 1 MeV. The results from experimental investigations along these lines are presented.

A setup for investigating the radiation protection properties of materials used in the manufacture of special protective clothing is described. The setup contains a collimated γ-ray source, a detector based on NaI (Tl) crystal, a movable platform for examining large areas of a material, and a data acquisition system based on a digital signal processor. A procedure for measuring the surface density of all absorbing elements in a material from the attenuation of γ-rays over a wide range of energies is described.

Results from experimental studies of the new non-gauge interaction using torsion balances in high-current magnets are described. Changes in the β decay rate and other parameters are analyzed. Thermal heating plants that use byuon energy with the new force for water heating are considered. Experiments are performed in Italy and Russia (2012–2016). The gravitational potential is used to produce the action of the new force. Heat is generated in vertical closed water circuits 5 to 12 m tall with pipe diameters of 0.1 m. The motion of the water is ensured with an electric pump. Experimental results show that the efficiency of electric-to-thermal energy conversion was greater than unity.

In modern studies, experimental methods for estimating nonlinear elastic moduli are often replaced with calculations of these quantities in mathematical simulation. However, different reliable models and experiments give different values of nonlinear elastic moduli. This work proposes a poßsible solution to the problem of which sets of elastic moduli should be used to predict the properties of substances. Two sets of the second-({c_αβ,γδ}), third-({c_αβ,γδ}), and fourth-order elastic moduli ({c_{αβ,γδ,μη,τρ}}) of hexagonal Gd crystal proposed in the literature are considered as examples. The elastic moduli are defined as partial derivatives of the nonequilibrium Landau potential Φ_L {u_αβ{ with respect to components of the tensor of homogeneous deformation of the crystal (Ü). Necessary information about the nonequilibrium Landau potential as a function of {u_αβ{ is given in the second section. An analytical way of deriving relationships between generally independent values of nonlinear elastic moduli caused by symmetry is proposed in Sections 3 and 4. The approach is based on using the integral rational basis of invariants (IRBI), which have the form of polynomials {u_aß{. Aspects of the theory of phase transitions based on IRBI are discussed in Section 3. The set of polynomials of the second, third, and fourth order included in the list of basic invariants {J_i^(P)}, and the form of Landau potential Φ({J_i^(P)}, are clearly defined. The forms of the chosen dependences {J_i^(P)} and (Φ_L{J_i^(P)}) are defined in Section 4 to compare the results from different works. Once the forms of Landau potential Φ_L{J_i^(P)} and Φ_L{u_αβ} are defined, they are compared. The comparison results allow derivation of the nontrivial relationships between the components of the third-C^III and fourth-rank elastic moduli tensors C^IV due Gd hexagonal symmetry. Two different sets of calculated elastic moduli of Gd crystals, found in two different works, are given in Section 5. The criteria for selecting the most suitable set of numerical values of elastic moduli are described in Sections 6 and 7. One criterion is a comparison of load limits calculated from isothermal Gd elastic moduli and experimentally determined numerical values of the limits of stability of a certain Gd phase. In the last section, we show how the criterion based on comparing the phase stability limits allows us to dertermine which sets of third-rank elastic moduli should be used in, e.g., predicting Raman spectra.