arXiv subjects

Yu. P. Lyakhno

Publications and source records attributed to Yu. P. Lyakhno.

5 recordsLinked to original sources

arXiv2026

Role of tensor forces in nuclei

Recently, calculations of the ground states of the lightest nuclei have been performed using highly accurate data on realistic internucleon forces. In this paper, these results were used to describe the properties of nuclei with nucleon numbers $A>4$. Taking into account tensor forces leads to the conclusion that the four subsystems in the nucleus with zero nucleon orbital momenta are combined predominantly into the $^1S_0$ cluster. Subsystems with nonzero orbital momenta also combine into clusters with lower potential energy. This approach allows us to consistently explain the lifetime of the $^8$Be nucleus, the Hoyle state, the sequential mechanism of the reaction with the emission of $α$ particles, the shift of the reaction threshold, and more. The assumption of the existence of a one-dimensional effective interaction of nucleons in the nucleus leads to the conclusion that the nucleus contains a "power center" and, accordingly, nucleons have orbital angular momenta relative to this "power center." Our approach does not predict the presence of such a "power center" in the nucleus.

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arXiv2020

Analysis of $^4$He($γ,p)$T and $^4$He($γ,n)$$^3$He Reactions with Linearly Polarized Photons in the Energy Range up to 100\,MeV

In a number of investigations, one can find the data on the $^4$He($γ$,p)T and $^4$He($γ$,n)$^3$He reaction cross sections in the collinear geometry, which are due to spin {\it S}=1 transitions of the final-state particles. The ratio of the differential cross section in the collinear geometry to the differential reaction cross section at the nucleon emission angle $θ_N$=90$^\circ$, and specified by the {\it S}=0 electric dipole transition at photon energies in the range 20$\le E_γ\le$100\,MeV, is independent of the photon energy, within the experimental error. In the meantime, experiments were made to measure the asymmetry of the cross section $Σ(θ_N)$, for the mentioned reactions with linearly polarized photons. It has been found that in the energy range between 20 and 90\,MeV, the $Σ(θ_N)$ value is also independent of the photon energy, within the experimental error. These data are in agreement with the assumption that transitions with spin {\it S}=1 can be due to the contribution of $^3P_0$ states of the $^4$He nucleus, and are inconsistent with the assumption that the spin-flip of the particle system occurred during the reaction as a result of the meson exchange current contribution. The available measured data on the collinear geometry reaction cross sections and the ones on the cross-section asymmetry of the reaction with linearly polarized photons do not agree between themselves. The above mentioned reactions seem to be more convenient for measuring the degree of photon beams linear polarization than the deuteron photodisintegration reactions.

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arXiv2015

Possible measurement of P-states probability in the $^4$He nucleus

Using the experimental data on total {\it S}=1 transition cross-sections \, for $^4$He$(γ,p)$$^3$H and $^4$He$(γ,n)$$^3$He reactions as the base, the paper describes the possibility of measuring the probability of {\it P}-states in the $^4$He nucleus. The {\it S}=1 transitions may originate from $^3P_0$ states of the nucleus, or be the result of the spin-flip of the final-state particle system from $^1S_0$, or $^5D_0$ states of the $^4$He nucleus, and also as a result of the secondary effects. The analysis of the experimental data has suggested the conclusion that within the statistical error the ratio of the {\it S}=1 transition cross-sections in the collinear geometry to reaction cross-sections at polar nucleon-exit angle $θ_N$=$90^{\circ}$ $ν_p$ and $ν_n$ in the photon energy range 22$\le$E$_γ$$\le$100 MeV is independent of the photon energy. This is in agreement with the assumption that the {\it S}=1 transitions can originate from $^3P_0$ states of the $^4$He nucleus. Average values of magnitude $ν_p$ and $ν_n$ in the mentioned photon energy range are calculated $ν_p$=0.01$\pm$0.002 and $ν_n$=0.015$\pm$0.003. The errors are statistical only.

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arXiv2013

Few-Nucleon Systems: Notes about the Status and Results of Investigations

Radiation technologies have found wide application in power engineering, medicine, biology and other areas of human activities. However, theoretical calculations of nuclear reactions and, correspondingly, the interpretation of experimental results appear model-dependent. The model-independent calculation of the nuclear reaction must take into account the structure of the nuclear ground state, the final-state nucleon interaction and the contribution of meson exchange currents. These calculations can be carried out only with due regard for realistic NN and 3N forces between nucleons and also, with the use of exact methods of solving the many-body problem. In this technique it is expedient to conduct investigations of nuclear reactions as from few-nucleon systems in the energy area of the particles below the meson-producing threshold. The tensor part of NN interaction and 3NF,s generate the lightest nuclei states with nonzero orbital momenta of nucleons. These states in the lightest nuclei is conditioned the properties of inter-nucleonic forces, and therefore, similar effects should be observed unexceptionally in all nuclei. The review papers are generally devoted to three-nucleon systems. In this paper primary attention is given to the investigation of the $^4$He nucleus.

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arXiv2013

Differential cross sections $^4$He({$γ$,p})$^3$H and $^4$He({$γ$,n})$^3$He reactions in the range of the photon energies up to the threshold of the meson production

Differential cross sections two-body ($γ,p$) and ($γ,n$) reactions of the $^4$He nucleus disintegration were measured using the bremsstrahlung beam of photons at the KIPT linac LEA-300 at the maximum energy ${\rm E}_γ^{max}$ = 150 MeV. The reaction products were detected in a diffusion chamber placed in the magnetic field. The differential cross sections were measured with a 1 MeV step up to a photon energy of 45 MeV, and with a greater step at higher energies. The step in the measurements of the polar angle of nucleon emission was ${10}^{\circ}$ in the c.m.s.

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