arXiv subjects

V. S. Vasilevsky

Publications and source records attributed to V. S. Vasilevsky.

At least 19 recordsLinked to original sources

arXiv2026

On three-cluster resonance structure of hypernuclei $_Λ^{7}$He, $_Λ^{7}$Li and $_Λ^{7}$Be

The bound and resonance states of hypernuclei $_Λ^{7}$He, $_Λ^{7}$Li and $_Λ^{7}$Be are studied within a three-cluster model. Within this model, hypernuclei $_Λ^{7}$He, $_Λ^{7}$Li and $_{Λ}^{7}$Be are considered as three-cluster systems $^{4}$He+$^2n$+$Λ$, $^{4}$He+$d$+$Λ$, $^{4}$He+$^2p$+$Λ$, respectively. Special attention is paid to determining resonance states in the three-cluster continuum of these hypernuclei and to study their nature. One semi-realistic nucleon-nucleon potential is employed to determine the internal structure of the clusters $^{4}$He, $^2n$, $d$ and $^2p$, and their interaction. Three versions of the nucleon-hyperon potential, known as the YNG potential, are employed to determine the interaction of the listed clusters with the lambda hyperon. A set of very narrow and fairly wide resonance states is found in the three-cluster continuum of $_Λ^{7}$He, $_Λ^{7}$Li and $_Λ^{7}$Be. The narrowest resonance states were detected in $_Λ^{7}$He and $_Λ^{7}$Li and their total width does not exceed 10 keV. The dominant decay channels of these resonance states are revealed.

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arXiv2025

Discrete and continuous spectrum of lightest hypernuclei

We analyze the peculiarities of the interaction of the lambda hyperon with s-shell nuclei. The spectra of bound and scattering states are studied in the hypernuclei $_Λ^{2}$H, $_Λ^{3}$H, $_Λ^{4}$H, $_Λ^{4}$He and $_Λ^{5}$He, which is considered as two-cluster configurations $p+Λ$, $d$+$Λ$, $^{3}$H+$Λ$, $^{3}$He+$Λ$, $^{4}$He+$Λ$, respectively. The explicit form of the folding potentials of such an interaction is presented in coordinate and oscillator representations, which help us to understand the structure of hypernuclei of interest. We compare energies of bound states, phase shifts of the elastic lambda hyperon, and neutron scattering from s-shell nuclei.

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arXiv2025

Many-channel microscopic cluster model of $^{8}$Be: S-factors

We investigate low--energy astrophysical $S$ factors for reactions proceeding through the $^{8}$Be compound system with entrance channels $p+{}^{7}$Li, $n+{}^{7}$Be, and $d+{}^{6}$Li. Using the same microscopic many--channel three--cluster framework as in our previous study of the high--lying $^{8}$Be spectrum, we calculate $S(E)$ for $^{7}$Li($p,α)^{4}$He, $^{7}$Be($n,α)^{4}$He, $^{7}$Be($n,p)^{7}$Li, $^{6}$Li($d,α)^{4}$He, $^{6}$Li($d,p)^{7}$Li, and $^{6}$Li($d,n)^{7}$Be in the energy range relevant for primordial and stellar nucleosynthesis. For the mirror pair $^{7}$Li($p,α)^{4}$He / $^{7}$Be($n,α)^{4}$He and for $^{7}$Be($n,p)^{7}$Li the calculated $S$ factors reproduce both the absolute scale and the low--energy trends of the experimental data within their quoted uncertainties, whereas the absolute $S$ factors for the deuteron--induced channels on $^{6}$Li are underestimated at low energy, consistent with the shifted $^{6}$Li+$d$ threshold and the absence of a broad subthreshold $2^{+}$ structure in the present implementation. A partial--wave analysis identifies the dominant $J^π$ contributions in each channel and relates them to specific $^{8}$Be resonances, while demonstrating that cluster polarization, previously shown to be crucial for the $^{8}$Be spectrum, is likewise essential for the normalization and energy dependence of several $S$ factors. Evaluating $S(E)$ at appropriate Gamow energies, we obtain a hierarchy of reaction channels that quantifies the relative importance of neutron-- and deuteron--induced processes for the production and destruction of $^{7}$Li and $^{7}$Be.

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arXiv2025

Structure of hypernucleus $_Λ^{7}$Li within microscopic three-cluster model

The structure of bound and resonance states of the hypernucleus $_Λ^{7}$Li is studied within a three-cluster model. This nucleus is considered a three-cluster structure consisting of $^{4}$He, a deuteron, and a lambda hyperon. The chosen three-cluster configuration allows us to describe more accurately the structure of hypernucleus $_Λ^{7}$Li and the dynamics of different processes that involve interactions of lightest nuclei and hypernuclei. The main goal of the present investigations is to find resonance states in the three-cluster continuum of $_Λ^{7}$Li and determine their nature. A set of narrow resonance states is detected at the energy range 0$<E\leq$2 MeV above the three-cluster threshold $^{4}$He+$d$+$Λ$.

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arXiv2025

Manifestation of quark effects in nuclei via bremsstrahlung analysis in the proton-nucleus scattering

\textbf{Background} (1) The incoherent emission of photons is dominant comparing to coherent one in proton-nucleus scattering. The incoherent bremsstrahlung is very sensitive to the magnetic moments of nucleons in nuclei. (2) According to the quark-meson coupling (QMC) model, the nucleon magnetic moments in nuclei are enhanced relative to those in vacuum, originating from the quark structure of nucleons. \textbf{Purpose} Investigate possibilities of observing quark effects in nuclei by the analysis of bremsstrahlung in nuclear reactions. \textbf{Methods} Analyse the bremsstrahlung cross sections with established model in proton-nucleus scattering, by extending with inclusion of in-medium modified nucleon magnetic moments in nuclei by the QMC model. \textbf{Results} (1) After calibrating the model without the quark effects for experimental data (TAPS Collaboration data for $p + \isotope[197]{Au}$), we calculate the cross sections and observe the slight difference between the spectra for models with and without quark effects. Such result is found for the first time, confirming possibilities of observing the quark effects in the spectra of bremsstrahlung. (2) As found, quark effects are not enough to be observed in middle and heavy nuclei, as they have dominant incoherent contributions. (3) \isotope[18]{C} has minimal incoherent contribution concerning other carbon isotopes, where the quark effects should be minimal. In ratios between the spectra for \isotope[18]{C} and \isotope[12]{C} with and without the quark effects the difference is clearly observed. \textbf{Conclusions} We establish the new physical observable for the quark effects in nuclei in the bremsstrahlung accompanied in the nuclear reactions, which can be measured. The present suggestion is for the first time in both theoretically and experimentally to study the quark effects in nuclei via the bremsstrahlung.

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arXiv2025

Many-channel microscopic cluster model of $^{8}$Be. I. Formation of high-energy resonance states

The nature and structure of high-energy resonance states in $^{8}$Be, located just below and above the $p+^{7}$Li threshold, are investigated in detail. A microscopic many-cluster and many-channel model is employed to study the formation of these resonances. This model includes three distinct three-cluster configurations: $^{4}$He+$^{3}$H+$p$, $^{4}$He+$^{3}$He+$n$, and $^{4}$He+$d$+$d$, enabling a comprehensive treatment of all major binary decay channels of $^{8}$Be, namely $^{4}$He+$^{4}$He, $p+^{7}$Li, $n+^{7}$Be, and $d+^{6}$Li. The primary focus of our analysis is the structure and dominant decay channels of the twin $1^{+}$, $2^{+}$, $3^{+}$, and $4^{+}$ resonance states. Additionally, we propose and implement a model to clarify how the $2^{+}$ resonance states lying below the $p+^{7}$Li threshold are formed. We demonstrate that these resonances are Feshbach-type states arising due to coupling of the open $^{4}$He+$^{4}$He channel with the closed channels $p+^{7}$Li, $n+^{7}$Be, and $d+^{6}$Li at these energies. Overall, the present approach provides a realistic description of the experimentally observed resonance spectrum near the $^7$Li+$p$ decay threshold, including negative-parity states $1^-$ and $2^-$. Our results are consistent with other microscopic calculations but offer more detailed insight into the internal structure and decay pathways of these resonances.

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arXiv2024

Theoretical analysis of the reactions induced by interaction of $^{6}$Li with nuclei $^{3}$H and $^{3}$He

We determine cross sections and astrophysical S-factors of the reactions generated in collisions between $^{6}$Li and $^{3}$H, and $^{6}$Li and $^{3}$He. A microscopic three-cluster model is employed to study the dynamics of reactions occurring in the mirror nuclei $^{9}$Be and $^{9}$B. In a previous study [Phys. Rev. C {\bf 109}, 045803 (2024)], this model was successfully applied to investigate the resonance structure of $^{9}$Be and $^{9}$B, as well as reactions induced by the interaction of deuterons with $^7$Li and $^7$Be. A fairly good agreement between theoretical results and available experimental data was achieved. To the best of our knowledge, appropriate experimental data for the astrophysical S-factors of the reactions generated by the interaction of $^6$Li with $^3$H and with $^3$He are currently unavailable. Thus, our results can serve as a guideline for future experimental efforts.

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arXiv2024

Study of structure of deuteron from analysis of bremsstrahlung emission in proton-deuteron scattering in cluster models

Purpose: In this paper we investigated emission of bremsstrahlung photons in the scattering of protons off deuterons within the microscopic cluster models in a wide region of the beam energy from low energies up to 1.5 GeV. Methods: Three-cluster model of bremsstrahlung is constructed for such a reaction. Formalism of the model includes form factor of deuteron which characterizes dependence of bremsstrahlung cross sections on structure of deuteron. This gives possibility to investigate the structure of nuclei from analysis of bremsstrahlung cross sections. Results: We studied dependence of the bremsstrahlung cross section on the structure of deuteron. We use three different shapes of the deuteron wave functions. Besides, we also calculate the cross section by neglecting internal structure of deuteron. Analysis of dependence of the cross section on such a parameter shows the following. (1) At beam energies 145 and 195 MeV used in experiments bremsstrahlung cross section is not sensitive visibly on variations of the shape of the deuteron wave functions. (2) Stable difference between cross sections calculated with and without internal structure of deuteron is observed at higher energy of beam (larger 500 MeV). (3) The spectrum is increased as we pass from structureless deuteron (the oscillator length $b=0$) to the deuteron discribed by the shell-model wave function (the realistic oscillator length) inside the full energy region of the emitted photons. Conclusion: Our cluster model is a suitable tool to study the structure of deuteron with high enough precision from bremsstrahlung analysis. We propose new experiments for such an investigation.

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arXiv2024

Pauli resonance states in light nuclei: how they appear and how they can be eliminated

Systematic analysis of parameters and properties of the Pauli resonance states are performed for light nuclei $^{6}$Li, $^{7}$Li, $^{8}$Be, $^{9}$Be and $^{10}$B, which are treated as two-cluster systems. The Pauli resonance states are redundant solutions of the resonating group method appearing when one try use more advanced description of the internal structure of interacting clusters. Our calculations are performed in a standard and advanced versions of the resonating group method. The standard version employs wave functions of many-particle shell model to describe internal motion of nucleons within each cluster. The advanced version is based on three-cluster resonating group method. As in the standard version, the internal wave functions of three clusters are approximated by wave functions of many-particle shell model model. However, in advanced version one of pair of clusters forms a bound state, and third cluster is considered to interact with such state. It is found that the Pauli resonance states in nuclei under consideration have energy between 11 and 46 MeV, and their widths vary from 8 keV to 6.7 MeV. Analysis of wave functions of Pauli resonance states and matrix elements of norm kernel allowed us to formulate an effective method for eliminating Pauli resonance states. It is demonstrated that this method effectively eliminate all determined the Pauli resonance states.

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arXiv2023

Many-channel microscopic theory of resonance states and scattering processes in $^{9}$Be and $^{9}$B

We present a many-channel microscopic model that extends the three-cluster model previously formulated in \cite{2009NPA...V37}. This extended model incorporates multiple three-cluster configurations, which are subsequently reduced to a comprehensive set of binary channels. These channels dictate the dynamics of various nuclear processes and the resonance structure of a compound nucleus across a broad energy spectrum. The application of this model focuses on investigating the nature of high-energy resonance states in $^{9}$Be and $^{9}$B, as well as the astrophysical $S$-factors for the reactions $^{7}$Li$(d,n)αα$ and $^{7}$Be$(d,p)αα$, particularly pertinent to the cosmological lithium problem. Parameterization of resonance states is performed across a wide range of total angular momenta and includes states of both positive and negative parity. Dominant decay channels are identified for each resonance state. Detailed analysis of astrophysical $S$ factors resulting from deuteron interactions with $^{7}$Li and $^{7}$Be is conducted within an energy range from zero to 2 MeV. Four exit channels in $^{9}$Be ($^{8}$Be($0^{+}$)$+n$, $^{8}$Be($2^{+}$)$+n$, $^{5}$He($3/2^{-}$)$+α$, $^{5}$He($1/2^{-}$)$+α$) and four in $^{9}$B ($^{8}$Be($0^{+}$)$+p$, $^{8}$Be($2^{+}$)$+p$, $^{5}$Li($3/2^{-}$)$+α$, $^{5}$Li($1/2^{-}$)$+α$) are considered. A clear hierarchy of reactions is established for the energy range 0$\leq E<$1.0 MeV. Notably, reactions $^{7}$Li$+d=^{8}$Be($0^{+}$)$+n$ and $^{7}$Be$+d=^{8}$Be($0^{+}$)$+p$ substantially dominate over all other reactions within this energy range. The model satisfactory describes the experimental astrophysical $S$ factors for these reactions.

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arXiv2023

Systematic study of bremsstrahlung emission in reactions with light nuclei in cluster models

A new model of bremsstrahlung emission in the scattering of light nuclei is constructed with main focus on strict cluster formulation of nuclear processes. Analysis is performed in frameworks of the folding approximation of the formalism with participation of $s$-nuclei. Reactions $p$ +$^4$He, $^2$D + $^4$He, $^3$H + $^4$He, $^3$He + $^4$He are included to analysis. Systematic analysis of properties of emission of bremsstrahlung photons in the wide region of kinetic energy of relative motion of two nuclei from 7 to 1000~MeV is performed. Influence of the oscillator length on the calculated spectra of bremsstrahlung emission is analyzed. On the example of $^3$H + $^4$He, dependence of the bremsstrahlung spectra on parameters of nuclear component of interacting potential is established (at first time for the light nuclei). Experimental bremsstrahlung data for the proton-deuteron scattering and proton-$α$-particle scattering are analyzed on the basis of this model.

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arXiv2022

The lowest excited states of 14C and 14O nuclei within a five-cluster model

We study the ground and the first excited $0^{+}$ states of two mirror nuclei $^{14}$C and $^{14}$O within a five-cluster model (three alpha-particles and two extra nucleons) with the use of high accuracy variational approach with Gaussian bases. The first excited $0^{+}$ state of these nuclei is shown to be connected with a change of the structure of the two-nucleon subsystem moving in the field of the $^{12}$C cluster. The density distributions, electric form factors (both the elastic and transition ones), pair correlation functions, and the momentum distributions of the constituent particles are found. The most probable shapes of five-cluster systems are revealed.

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arXiv2021

Structure of the ground and excited states in $_Λ^{9}$Be nucleus

We investigate properties of bound and resonance states in the $_Λ^{9}$Be nucleus. To reveal the nature of these states, we use a three-cluster $2α+Λ$ microscopic model. The model incorporates Gaussian and oscillator basis functions and reduces a three-cluster Schrödinger equation to a two-body like many-channel problem with the two-cluster subsystems ($_Λ^{5}$He and $^8$Be) being in a bound or a pseudo-bound state. Influence of the cluster polarization on the energy and widths of resonance states in $_Λ^{9}$Be and on elastic and inelastic $_Λ^{5}$He+$α$ scattering is analyzed.

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arXiv2020

Resonance structure of $^{8}$Be with the two-cluster resonating group method

A two-cluster microscopic model is applied to study elastic alpha-alpha scattering and resonance structure of $^{8}$Be. The model is an algebraic version of the Resonating Group Method, which makes use complete set of oscillator functions to expand wave function of two-cluster system. Interaction between clusters is determined by well-known semi-realistic nucleon-nucleon potentials of Hasegawa-Nagata, Minnesota and Volkov. Detail analysis of resonance wave functions is carried out in oscillator, coordinate and momentum spaces. Effects of the Pauli principle on wave functions of the $^{8}$Be continuous spectrum states are thoroughly studied.

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arXiv2019

Properties of a potential energy matrix in oscillator basis

Matrix elements of potential energy are examined in detail. We consider a model problem - a particle in a central potential. The most popular forms of central potential are taken up, namely, square-well potential, Gaussian, Yukawa and exponential potentials. We study eigenvalues and eigenfunctions of the potential energy matrix constructed with oscillator functions. It is demonstrated that eigenvalues coincide with the potential energy in coordinate space at some specific discrete points. We establish approximate values for these points. It is also shown that the eigenfunctions of the potential energy matrix are the expansion coefficients of the spherical Bessel functions in a harmonic oscillator basis. We also demonstrate a close relation between the separable approximation and $L^{2}$ basis (J-matrix) method for the quantum theory of scattering.

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arXiv2019

Effects of the Coulomb interaction on parameters of resonance states in mirror three-cluster nuclei

We investigate how the Coulomb interaction affects the energy $E$ and width $Γ$ of resonance states in mirror nuclei. We employ a three-cluster microscopic model to determine position of resonance states in two- and three-body continua. Two parameters are introduced to quantify effects of the Coulomb interactions. As the energy and width of the corresponding resonance states of mirror nuclei are displayed on an $E$-$Γ$ plane, these parameters determine a rotation and a dilatation. With the help of these parameters we found resonance states with strong, small and medium effects of the Coulomb interaction. We also found two different scenarios of the motion of resonance states due to the Coulomb interaction. The first standard (major) scenario represent resonance states with the larger energy and larger width than their counterparts have. The second rear scenario includes resonance states with the larger energy but smaller width.

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arXiv2019

Influence of the Pauli principle on two-cluster potential energy

We study effects of the Pauli principle on the potential energy of two-cluster systems. The object of the investigation is the lightest nuclei of p-shell with a dominant $α$-cluster channel. For this aim we construct matrix elements of two-cluster potential energy between cluster oscillator functions with and without full antisymmetrization. Eigenvalues and eigenfunctions of the potential energy matrix are studied in detail. Eigenfunctions of the potential energy operator are presented in oscillator, coordinate and momentum spaces. We demonstrate that the Pauli principle affects more strongly the eigenfunctions than the eigenvalues of the matrix and leads to the formation of resonance and trapped states.

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arXiv2019

How the antisymmetrization affects a cluster-cluster interaction: two-cluster systems

We study effects of the antisymmetrization on the potential energy of two-cluster systems. The object of the investigation is the lightest nuclei of p-shell with a dominant alpha-cluster channel. For this aim we construct matrix elements of two-cluster potential energy between cluster oscillator functions with and without full antisymmetrization. Eigenvalues and eigenfunctions of the potential energy matrix are studied in detail. Eigenfunctions of the potential energy operator are presented in oscillator, coordinate and momentum spaces. We demonstrate that the Pauli principle affects more strongly the eigenfunctions than the eigenvalues of the matrix and leads to the formation of resonance and trapped states.

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