arXiv subjects

D. A. Savin

Publications and source records attributed to D. A. Savin.

11 recordsLinked to original sources

arXiv2026

Determination of asymptotic normalization coefficients for the $^{7}$Li$\to \alpha + ^{3}$He channel

Asymptotic normalization coefficients (ANCs) $C_{3/2}$ and $C_{1/2}$ for the channels $^7$Li$(3/2^-;0$ MeV)$\to \alpha+^3$H and $^7$Li$(1/2^-;0.478$ MeV)$\to \alpha+^3$H, respectively, were determined by analyzing elastic $\alpha^3$H- scattering data using three different methods. All three methods yield similar results. The ANC values averaged over the three methods are $C_{3/2}=2.08\pm 0.10$ fm$^{-1/2}$ and $C_{1/2}=2.00\pm 0.10$ fm$^{-1/2}$. Comparison of the found ANCs with the previously obtained ANCs for $^7$Be confirms the relationship linking the ANC values for mirror nuclei. This research on determining the ANCs for the $^7$Li nucleus is, to some extent, a continuation of the previously completed study on its mirror nucleus, $^7$Be [ D. A. Savin, L. D. Blokhintsev, B. F. Irgaziev, A. S. Kadyrov, and A. M. Mukhamedzhanov, Phys. Rev. C 112, 065807 (2025)].

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arXiv2025

Determination of Asymptotic Normalization Coefficients Based on the Dispersive Optical Model

A method for determining asymptotic normalization coefficients for removing nucleons from nuclei is proposed. It is based on the use of the dispersive optical model potential. Within the method, the strength parameter of the Hartree- Fock type potential at the Fermi energy is the only one fitting parameter. It was found that adjusting this parameter allows us to achieve a coincidence of the calculated binding energies with the experimental ones accurately enough. Specific calculations were carried out for 17O, 17F, 41Ca, and 41Sc nuclei. An acceptable agreement with the results of other works, which are characterized by a noticeable spread, was achieved.

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arXiv2024

Asymptotic normalization coefficients for $α+ {}^{12}{\rm C}$ synthesis and the $S$-factor for ${}^{12}{\rm C}(α, \,γ){}^{16}{\rm O}$ radiative capture

The $^{12}{\rm C}(α,γ)^{16}$O reaction, determining the survival of carbon in red giants, is of interest for nuclear reaction theory and nuclear astrophysics. A specific feature of the $^{16}$O nuclear structure is the presence of two subthreshold bound states, (6.92 MeV, 2$^+$) and (7.12 MeV, 1$^-$), that dominate the behavior of the low-energy $S$-factor. The strength of these subthreshold states is determined by their asymptotic normalization coefficients (ANCs), which need to be known with high accuracy. Recently, using a model-independent extrapolation method, Blokhintsev {\it et al.} [Eur. Phys. J. A {\bf 59} (2023) 162] determined the ANCs for the $α$-particle removal taking into account three subthreshold states in $^{16}$O. The goal of this paper is to address four main problems elucidating the impact of the subthreshold ANCs on the low-energy $S$-factor. Firstly, we analyse the connection between variations of the subthreshold ANCs and the low-energy $S$-factor, in particular, at the most effective energy of $300$ keV. Secondly, we calculate contributions to the $S(300\,{\rm keV})$-factor from the subthreshold $1^{-}$ and $2^{+}$ resonances, that are controlled by the subthreshold ANCs. We also evaluate the contribution of the uncertainties of the subthreshold ANCs to the budget of the low-energy $S$-factor uncertainty, especially, the $S(300\,{\rm keV})$-factor. Thirdly, we analyse interference of the subthreshold resonances (SRs) with higher resonances and with the $E1$ and $E2$ direct captures to the ground state. Finally, we investigate a correlated effect of the subthreshold and ground-state ANCs on the low-energy $S$-factor and, in particular, on the $S(300\,{\rm keV})$-factor.

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arXiv2023

Asymptotic normalization coefficients of alpha-particle removal from $^{16}$O($3^-,2^+,1^-$)

Asymptotic normalization coefficients (ANC) determine the overall normalization of cross sections of peripheral radiative capture reactions. In a recent paper [Blokhintsev et al., Eur. Phys. J. A 58, 257 (2022)], we considered the ANC $C_0$ for the virtual decay $^{16}$O$(0^+; 6.05$ MeV)$\to α+^{12}$C(g.s.). In the present paper, which can be regarded as a continuation of the previous, we treat the ANCs $C_l$ for the vertices $^{16}$O$(J^π)\to α+^{12}$C(g.s.) corresponding to the other three bound excited states of $^{16}$O ($J^π=3^-$, $2^+$, $1^-$, $l=J$). ANCs $C_l$ ($l=3,\,2,\,1$) are found by analytic continuation in energy of the $α^{12}$C $l$-wave partial scattering amplitudes, known from the phase-shift analysis of experimental data, to the pole corresponding to the $^{16}$O bound state and lying in the unphysical region of negative energies. To determine $C_l$, the scattering data are approximated by the sum of polynomials in energy in the physical region and then extrapolated to the pole. For a more reliable determination of the ANCs, various forms of functions expressed in terms of phase shifts were used in analytical approximation and subsequent extrapolation.

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arXiv2022

Determination of asymptotic normalization coefficients for the channel $^{16}$O$\to α+^{12}$C. Excited state $^{16}$O($0^+; 6.05$ MeV)

Asymptotic normalization coefficients (ANC) determine the overall normalization of cross sections of peripheral radiative capture reactions. In the present paper, we treat the ANC $C$ for the virtual decay $^{16}$O$(0^+; 6.05$ MeV)$\to α+^{12}$C(g.s.), the known values of which are characterized by a large spread $(0.29-1.65)\times 10^3$ fm$^{-1/2}$. The ANC $C$ is found by analytic continuation in the energy of the $α^{12}$C $s$-wave scattering amplitude, known from the phase-shift analysis of experimental data, to the pole corresponding to the $^{16}$O bound state and lying in the unphysical region of negative energies. To determine $C$, two different methods of analytic continuation are used. In the first method, the scattering data are approximated by the sum of polynomials in energy in the physical region and then extrapolated to the pole. The best way of extrapolation is chosen on the basis of the exactly solvable model. Within the second approach, the ANC $C$ is found by solving the Schrödinger equation for the two-body $α^{12}$C potential, the parameters of which are selected from the requirement of the best description of the phase-shift analysis data at a fixed experimental binding energy of $^{16}$O$(0^+; 6.05$ MeV) in the $α+^{12}$C channel. The values of the ANC $C$ obtained within these two methods lie in the interval (886--1139) fm$^{-1/2}$.

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arXiv2019

New method of analytic continuation of elastic-scattering data to the negative-energy region and asymptotic normalization coefficients for $^{17}$O and $^{13}$C

A new method is proposed for extrapolation of elastic-scattering data to the negative-energy region for a short-range interaction. The method is based on the analytic approximation of the modulus-squared of the partial-wave scattering amplitude. It is shown that the proposed method has an advantage over the traditional one based on continuation of the effective-range function. The new method has been applied to determine the asymptotic normalization coefficients for the $^{17}$O and $^{13}$C nuclei in the $n+^{16}$O and $n+^{12}$C channels, respectively.

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arXiv2018

Extrapolation of scattering data to the negative-energy region. Application to the $p-^{16}$O system

The problem of analytic continuation of the scattering data to the negative-energy region to obtain information on asymptotic normalization coefficients (ANCs) of bound states is discussed. It is shown that a recently suggested $Δ$ method [O.L.Ram\'ırez Suárez and J.-M. Sparenberg, Phys. Rev. C {\bf 96}, 034601 (2017)] is not strictly correct in the mathematical sense since it is not an analytic continuation of a partial-wave scattering amplitude to the region of negative energies. However, it can be used for practical purposes for sufficiently large charges and masses of colliding particles. Both the $Δ$ method and the standard method of continuing of the effective range function are applied to the $p-^{16}$O system which is of interest for nuclear astrophysics. The ANCs for the ground $5/2^+$ and excited $1/2^+$ states of $^{17}$F are determined.

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arXiv2017

Extrapolation of scattering data to the negative-energy region II

A problem of analytical continuation of scattering data to the negative-energy region to obtain information about bound states is discussed within an exactly solvable potential model. This work is continuation of the previous one by the same authors [L. D. Blokhintsev et al., Phys. Rev. C 95, 044618 (2017)]. The goal of this paper is to determine the most effective way of analytic continuation for different systems. The $d+α$ and $α+^{12}$C systems are considered and, for comparison, an effective-range function approach and a recently suggested $Δ$-method [O. L. Ram\'ırez Suárez and J.-M. Sparenberg, Phys. Rev. C 96, 034601 (2017)] are applied. We conclude that the $Δ$-method is more effective for heavier systems with large values of the Coulomb parameter, whereas for light systems with small values of the Coulomb parameter the effective-range function method might be preferable.

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arXiv2016

Extrapolation of scattering data to the negative-energy region

Explicit analytic expressions are derived for the effective-range function for the case when the interaction is represented by a sum of the short-range square-well and long-range Coulomb potentials. These expressions are then transformed into forms convenient for extrapolating to the negative-energy region and obtaining the information about bound-state properties. Alternative ways of extrapolation are discussed. Analytic properties of separate terms entering these expressions for the effective-range function and the partial-wave scattering amplitude are investigated.

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arXiv2011

Collimation of a Circulating Beam in the U_70 Synchrotron by Use of Reflections in Axially - Oriented Crystals

The possibilities of the extraction and collimation of a circulating beam by a new method due to the reflection of particles in crystals with axial orientation were experimentally investigated in the Fall-2010 run at the U_70 synchrotron. Such crystals have positive features, because the axial potential is five times larger than the planar potential. It has been shown that the collimation efficiency can reach 90% due to axial effects in the crystal. Losses of the circulating beam on a collimator have been reduced by several times; this makes it possible to suppress the muon jet near the steel collimator of the circulating beam.

physics.acc-ph↗

arXiv2011

Crystal-Assisted Beam Extraction and Collimation at the U-70 Circular Accelerator

New crystal technique - array of bent strips and a fan-type reflector, based on thin straight plates - have been used for research of extraction and collimation a circulating beam in the U-70 accelerator at the energy 50 GeV and 1.3 GeV. It is shown, that new devices can effectively steer a beam in a wide energy range. For protons with energy 50 GeV efficiency of extraction and collimation about 90 % has been achieved which is record for this method. Reduction of particle losses in 2-3 times was observed also in accelerator at application of different crystals in comparison with the usual one-stage collimation scheme of beam with a steel absorber.

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