arXiv subjects

L. D. Blokhintsev

Publications and source records attributed to L. D. Blokhintsev.

14 recordsLinked to original sources

arXiv2026

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

Asymptotic normalization coefficients (ANCs) $C_{3/2}$ and $C_{1/2}$ for the channels $^7$Li$(3/2^-;0$ MeV)$\to α+^3$H and $^7$Li$(1/2^-;0.478$ MeV)$\to α+^3$H, respectively, were determined by analyzing elastic $α^3$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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arXiv2021

Astrophysical S factor and rate of $^{7}{\rm Be}(p, γ)^{8}{\rm B}$ direct capture reaction in a potential model

The astrophysical $^7{\rm Be}(p, γ)^8{\rm B}$ direct capture process is studied in the framework of a two-body single-channel model with potentials of the Gaussian form. A modified potential is constructed to reproduce the new experimental value of the $S$-wave scattering length and the known astrophysical $S$ factor at the Gamow energy, extracted from the solar neutrino flux. The resulting potential is consistent with the theory developed by Baye [Phys. Rev. C {\bf 62} (2000) 065803] according to which the $S$-wave scattering length and the astrophysical $S$ factor at zero energy divided by the square of ANC are related. The obtained results for the astrophysical $S$ factor at intermediate energies are in good agreement with the two data sets of Hammache {\it et al.} [Phys. Rev. Lett. {\bf 86}, 3985 (2001); {\it ibid.} {\bf 80}, 928 (1998)]. Linear extrapolation to zero energy yields $ S_{17}(0) \approx (20.5 \pm 0.5) \, \rm eV \, b $, consistent with the Solar Fusion II estimate. The calculated reaction rates are substantially lower than the results of the NACRE II collaboration.

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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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arXiv2018

Nucleon-$α$ Scattering and Resonances in $^5$He and $^5$Li with JISP16 and Daejeon16 $NN$ interactions

The SS-HORSE approach to analysis of resonant states is generalized to the case of charged particle scattering utilizing analytical properties of partial scattering amplitudes and applied to the study of resonant states in the $^{5}$Li nucleus and non-resonant $s$-wave proton-$α$ scattering within the no-core shell model using the JISP16 and Daejeon16 $NN$ interactions. We present also the results of calculations of neutron-$α$ scattering and resonances in the $^{5}$He nucleus with Daejeon16 and compare with results published previously using JISP16.

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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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arXiv2007

Trojan Horse as an indirect technique in nuclear astrophysics. Resonance reactions

The Trojan Horse method is a powerful indirect technique that provides information to determine astrophysical factors for binary rearrangement processes $x + A \to b + B$ at astrophysically relevant energies by measuring the cross section for the Trojan Horse reaction $a + A \to y+ b + B$ in quasi-free kinematics. We present the theory of the Trojan Horse method for resonant binary subreactions based on the half-off-energy-shell R matrix approach which takes into account the off-energy-shell effects and initial and final state interactions.

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arXiv2005

Indirect techniques in nuclear astrophysics. Asymptotic Normalization Coefficient and Trojan Horse

Owing to the presence of the Coulomb barrier at astrophysically relevant kinetic energies it is very difficult, or sometimes impossible, to measure astrophysical reaction rates in the laboratory. That is why different indirect techniques are being used along with direct measurements. Here we address two important indirect techniques, the asymptotic normalization coefficient (ANC) and the Trojan Horse (TH) methods. We discuss the application of the ANC technique for calculation of the astrophysical processes in the presence of subthreshold bound states, in particular, two different mechanisms are discussed: direct capture to the subthreshold state and capture to the low-lying bound states through the subthreshold state, which plays the role of the subthreshold resonance. The ANC technique can also be used to determine the interference sign of the resonant and nonresonant (direct) terms of the reaction amplitude. The TH method is unique indirect technique allowing one to measure astrophysical rearrangement reactions down to astrophysically relevant energies. We explain why there is no Coulomb barrier in the sub-process amplitudes extracted from the TH reaction. The expressions for the TH amplitude for direct and resonant cases are presented.

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arXiv1998

Backward Elastic p3He Scattering at Energies 1 - 2 GeV

The two-body transfer amplitude for the rearrangement process i+(jkl) - j+(ikl) is constructed on the basis of technique of 4-dimensional covariant nonrelativistic graphs. The developed formalism is applied to describing backward elastic $p^3He$ scattering in the energy range 0.5 - 1.7 GeV. Numerical calculations performed using the 5- channel wave function of the $^3He$ nucleus show that the transfer of a noninteracting np- pair dominates and explains satisfactorily the energy and angular dependence of the differential cross section at energies 0.9 - 1.7$ GeV. A weak sensitivity to high momentum components of the $~^3He$ wave function in spite of large momentum transfer as well as a very important role of rescatterings in the initial and final states are established.

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