Том 83, № 4 (2019)

Characteristics of a new separator of radioactive ion beams (RIBs) are described. It was recently commissioned at the Flerov Laboratory of Nuclear Reactions (FLNR JINR) and is in operation at the primary beam line of the U-400M heavy ion cyclotron providing RIBs in energy range of 10–50 MeV/nucleon. Preliminary results obtained in the first experiments performed with this separator in 2018 are presented. A medium-term program of scientific research is discussed.

The kinetic energy spectra of intermediate mass fragments (IMF) has been studied for 4.4 GeV d + Au collisions at the Dubna Nuclotron with the 4π detector array FASA. Experimental kinetic energy spectra were compared to that obtained by the multi-body Coulomb trajectory calculations with the initial break-up conditions given by the combined model INC + SMM. It was found good agreement of measured and calculated kinetic energy spectra including a radial flow.

The energy and the square of the wave function modulus for the ground state of ^{6, 7, 11}Li nuclei are calculated using Feynman continual integrals in the model of the interaction between a nuclear core and external nucleons. The obtained energy values are in good agreement with the experimental data. The appearance of deuteron and triton clusters was demonstrated in the structure of ⁶Li and ⁷Li nuclei, respectively. Calculations in the shell model of a deformed nucleus are also performed for ^{7, 9, 11}Li nuclei. Both models help explain the strong deformation of the ⁷Li nucleus.

The contribution from the mechanism of heavy ²³Na cluster stripping from a ²⁷Al(5/2⁺) initial nucleus to a cross section of the ²⁷Al(р, α)²⁴Mg(0⁺, 2⁺) reaction is calculated at E_p = 7.4 MeV and angles of α‑particle emission of 25°–160° (laboratory). Calculations are made with the FRESCO code using the contribution from the 3/2⁺ ground state of ²³Na. Spectroscopic amplitudes at decay vertices of ²⁷Al(5/2⁺) → ²³Na(3/2⁺) + α and ²⁴Mg(0⁺, 2⁺) → ²³Na(3/2⁺) + р reactions are determined from wave functions in the context of the Nilsson model, depending on their deformation. Cross sections calculated for the 0⁺ and 2⁺ levels of the ²⁴Mg nucleus are two orders of magnitude lower than those found experimentally. The cross section for the 0⁺ level grows at θ_α ∼ 180° in the back semi-sphere, while the one for the 2⁺ level exhibits a maximum at θ_α > 140°. The slight contribution from the mechanism of heavy cluster stripping is due to the spectroscopic amplitudes at the decay vertices of the initial and final nuclei owing to a weak overlap of wave functions of ²⁷Al, ²³Na, and ²⁴Mg(0⁺, 2⁺) nuclei in the Nilsson model.

It is proposed that deuteron quasi-free scattering on separate clusters of the ⁹Be nucleus be used to estimate the contributions from different cluster configurations (⁸Be + n, α + α + n, α + ⁵He) to the structure of ⁹Be. These scattering processes are modeled kinematically. It is shown there are isolated regions in the angular and energy distributions of secondary particles that correspond to certain configurations of the clusters in ⁹Be are identified. The modeling results show the obtained data on the energies and angles of emission of two secondary particles (d + n and d + α) allow us to identify the contributions from different reaction channels and draw conclusions regarding the cluster structure of the ⁹Be nucleus. The results from this analysis are employed in the inclusive exclusive experimental investigations of the ⁹Be cluster structure using the deuteron beam at Moscow State University’s Skobeltsyn Institute of Nuclear Physics.

The possibility is considered of reconstructing the thermal neutron flux density of a W–Be photoneutron source via neutron activation analysis of Ag, Mg, Fe, Mn, and Ti samples. The use of a simple function in the form AE^−B describing the thermal region of the spectrum is discussed as an example of reconstruction. The dependence of the reaction rates’ deviation from the ones calculated on the parameters of the approximating function is investigated. The convergence of the reconstruction results as the number of experimental data grows is obtained. This means of recovery can be used for operational measurements of the thermal neutron flux density of the photoneutron source and to optimize the parameters of the source.

Independent estimates are presented for two important characteristics of the photonuclear ¹³C(γ, p)¹²B activation detection of hidden carbon concentrations: the numbers of ¹²B isotope nuclei that are produced and the fluxes of secondary γ quanta upon the decay of ¹²B nuclei. The findings are compared to known experimental data and the results from earlier model calculations.

Experimental data for ^{140, 142}Се and ¹⁵³Eu nuclei are analyzed jointly using the cross sections for total and partial photoneutron reactions obtained with quasimonoenergy photon beams formed during the annihilation of relativistic positrons. The results from an experiment performed on a bremsstrahlung beam are also used for such an analysis for the ¹⁵³Eu nucleus. Well-known systemic discrepancies between the results of different experiments are analyzed using the objective physical criteria of data reliability, and ways of allowing for them are considered. New data on the cross sections of (γ, 1n) and (γ, 2n) reactions for ^140, 142Се nuclei, on the cross section of (γ, 3n) reaction for ¹⁵³Eu nucleus, and on the cross section of total photoneutron reaction for all three nuclei were obtained additionally the cross sections of partial reactions that satisfy the established criteria of reliability. It was shown that substantial deviations of the experimental reaction cross sections from those evaluated are due to an unreliable sorting of neutrons between the channels with a multiplicity of 1, 2 due to the abovementioned systematic uncertainties.

The structure of the levels of heavy helium isotope ⁸He is investigated using the reactions of stopped-pion absorption by carbon isotopes ¹²С(π⁻, p³He)X, ¹⁴С(π⁻, d⁴He)X, and ¹⁴С(π⁻, t³He)X. Measurements are made with the two-arm multilayer semiconductor spectrometer at the LANL accelerator. Excited states of the ⁸He nucleus with energies of excitation of up to ~ 20 MeV are sought using the measured missing-mass spectra for these reactions. An excited state with E_x ≈ 6.4 MeV and Г ≤ 1 MeV is observed for the first time. Its structure is probably due to two valence nucleons on the (1p_1/2)² shell.

The resonance structure of charge-exchange strength function S(E) and its effect on the cross sections of neutrino capture by ⁷¹Ga, ⁹⁸Mo, and ¹²⁷I were examined using the self-consistent theory of finite Fermi systems. Gamow–Teller, analog, and lower-lying pygmy resonances are considered in calculating strength function S(E). Cross sections σ(E) of solar neutrino capture are calculated for the above three isotopes with the resonance structure of strength function S(E) factored in, and the influence of each resonance on energy dependence σ(E) is analyzed. It is found that all charge-exchange resonances in strength function S(E) must be considered in calculating cross section σ(E). Even if just the high-lying resonances are neglected, cross section σ(E) can be underestimated, and this could affect the interpretation of experimental data.

A family of leptons based on charged \({{l}_{{{\text{ch}}}}}\) and neutral (neutrino) \({{l}_{\nu }}\) quantum numbers is described while retaining their sum \({{L}_{{{\text{ch}}}}}\) and total aroma \({{L}_{\nu }}.\) Representations of a four-component neutrino theory are expanded by including a tauon family and a new (fourth) lepton family. (Non)diagonal lepton processes are studied with respect to the interaction between neutral (NC) and charged (CC) weak currents. It is shown that information on current constants can be obtained by measuring the recoil electron spectra and total cross sections of elastic \(\nu e\) and \(\tilde {\nu }e\) types of scattering.

Different mass relations for estimating neutron–proton correlations are analyzed. The differences between the estimates indicate phenomenologocal distinction between the considered relations. Parametrization with a shell model is used to clarify the structure of different estimates and their correspondence to the real value of np-correlations.

The results are presented from an experiment to measure the probabilities of γ-quanta emission from the first excited states of daughter nuclei formed in α-decay chain of the ²²⁶Ra nucleus. The use of fast temporal digitizers of the shape of the signal from a semiconductor α-detector and a germanium γ-detector of large volume allows the probabilities of the decay of the first excited states to be estimated at the level of 10^–5 from the main mode of decay.