Three-Body Calculation of the 4He（aH,γ）7Li and 4He（aHe,γ）7Be Reactions and Structure of the 7Li and 7Be at Solar Energies

The two 3H＋4He and 3He＋4He fusion reactions at low energies are usually viewed as an approximate external capture process. We study the 4He（3H,γ）rLi and 4He（SHe,γ）7Be reactions in a cluster model, which can take into account two- and three-body electromagnetic currents, using minimal substitution in the explicit momentum dependence of the two- and three-cluster interactions. Our main goal is to explore how the cross section of the low-energy 3H＋4He or 3He＋4He capture reactions depends on energy. The astrophysical S-factors for these reactions are calculated at very low energies. We construct the conserved realistic Argonne v18 for two nucleons and Urbana IX or Tucson-Melbourne three-cluster interactions, which are considered for calculation. We also calculate the binding energies and the structural properties of a Hq-4He or 3He＋4 He systems. The binding energies are found to be -37.72 （-36.32） MeV and -39.35 （-37.43） MeV, with （without） three-body interactions for 7Be and 7 Li, in satisfactory agreement with other theoretical results and experimental data, respectively.     

Microscopic calculation of the 3He(α,γ)7Be and 3H(α,γ)7Li capture cross sections using realistic interactions

The radiative capture cross sections for the 3He(α,γ)7Be and 3H(α,γ)7Li reactions are calculated in the fully microscopic fermionic molecular dynamics approach using a realistic effective interaction that reproduces the nucleon-nucleon scattering data. At large distances bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states. At short distances the many-body Hilbert space is extended with additional many-body wave functions needed to represent polarized clusters and shell-model-like configurations. Properties of the bound states are described well, as are the scattering phase shifts. The calculated S factor for the 3He(α,γ)7Be reaction agrees very well with recent experimental data in both absolute normalization and energy dependence. In the case of the 3H(α,γ)7Li reaction the calculated S factor is larger than available experimental data by about 15%.     

Tensor Force Manifestations in ab Initio Study of the 2H(d, γ)4He, 2H(d, p)3H, and 2H(d, n)3He Reactions

The ²H(d, γ)⁴He capture reaction and the ²H(d, p)³H and ²H(d, n)³He transfer reactions at very low energies are studied in an extended microscopic cluster model with a realistic nucleon–nucleon force. Our results show that the tensor force in realistic interactions plays an essential and indispensable role to reproduce the very low-energy astrophysical S factor of these reactions.     

The 3He(α, γ)7Be and 3He(α, γ)7Li reactions at astrophysical energies

The radiative capture cross sections for ³He(α, γ)⁷Be and ³He(α, γ)⁷Li at astrophysical energies have been studied microscopically in terms of the resonating group method. It was found that the astrophysical S-factors correlate strongly to the nuclear size and deformation of ⁷Be and ⁷Li. With the help of measured nuclear properties of these nuclei, a safety range of the absolute values of the S-factor was determined; the most recommended S(0)-values are 0.50 ± 0.03 keV · b for the ³He(α, γ)⁷Be reaction and 0.098 ± 0.006 keV · b for the ³H(α, γ)⁷Li reaction.     

Determination of the nuclear vertex constants for the 7Be ↔ 3He4He vertex using theN/D equations and calculation of the astrophysical S factor for the 4He(3He, γ)7Be reaction

N/D equations taking into account the Coulomb interaction effects are used to consider the phase analysis data on ³He⁴He scattering and determine the nuclear vertex constants for the ⁷Be ? ³He⁴He vertex, where the beryllium nucleus is in the ground (3/2^?) or first excited (1/2^?) states. Information about the asymptotic normalization coefficients of the wave functions of the ⁷Be nucleus in the noted states is derived. The data obtained are used to calculate the astrophysical S factor for the ⁴He(³He, γ)⁷Be reaction.     

Tensor force manifestations in ab initio study of the 2H(d,γ)4He, 2H(d,p)3H, and 2H(d,n)3He reactions

The (2)H(d,p)(3)H, (2)H(d,n)(3)He, and (2)H(d,γ)(4)He reactions are studied at low energies in a multichannel ab initio model that takes into account the distortions of the nuclei. The internal wave functions of these nuclei are given by the stochastic variational method with the AV8' realistic interaction and a phenomenological three-body force included to reproduce the two-body thresholds. The obtained astrophysical S factors are all in very good agreement with the experiment. The most important channels for both transfer and radiative capture are identified by comparing to calculations with an effective central force. They are all found to dominate thanks to the tensor force.     

Inelastic production of neutral pions in the4He(γ, πℴp)3H reaction

The yield of the⁴He(, p)³H reaction has been studied in a bremsstrahlung beam of photons with a maximum energy of 450 MeV. The measurements were made on an experimental setup consisting of a total absorption Cerenkov gamma spectrometer and a helium streamer chamber. A kinematic analysis is made of the angular distributions of the disintegration products of the⁴He nucleus to study the mechanism of inelastic photoproduction of neutral pions. The relatively high event density in the region of small proton-triton separation angles is attributable to the quasielastic mechanism of the reaction in which pion photoproduction is accompanied by excitation of the⁴He nucleus.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 51–56, September, 1989.     

Study of the reaction 12C(γ, n 3He)2α

The possibility of separating, with the aid of photoemulsion, channels of the reaction ¹²C(γ, n ³He)2α that involve the formation of ⁷Be and ⁸Be intermediate nuclei in excited states is studied. The experimental energy distributions of these nuclei are obtained. The relative yields from these reaction channels are estimated.     

Description of the 7Li(γ, n)6Li process in the potential cluster approach

The direct mechanism for the photodisintegration process (γ, n₀) in the energy range from the threshold to 9 MeV is considered within the framework of the αt-model representation of the ⁷Li nucleus with allowance for the E1 and M1 transitions. Integral and differential cross sections and asymmetry of photoneutrons in the reaction with linearly polarized photons are calculated. The results are compared with the available experimental data and theoretical calculations.     

New determination of the ~7Be ground state spectroscopic factor and the ~6Li(p,γ)~7Be astrophysical S(E) factors

The 'lithium problem, in Big Bang nucleosynthesis(BBN) has recently focused on reactions involving ~7 Be.The ~6 Li(p,γ)~7 Be reaction can provide us not only with information about ~6 Li destruction but also with information about ~7 Be production. In the present work, the proton spectroscopic factor in ~7 Be is extracted to be 0.70 ± 0.17 from the angular distribution of ~7 Be(d, ~3 He)~6 Li at E_(c.m.) = 6.7 MeV. This value is then used to compute the direct component of the astrophysical ~6 Li(p,γ)~7 Be_(g.s.) S(E) factors and determine the resonance parameters from the total S(E) factors.     

Photodisintegration cross section of the reaction (4)He(γ,p)(3)H between 22 and 30 MeV

The two-body photodisintegration cross section of (4)He into a proton and triton was measured with monoenergetic photon beams in 0.5 MeV energy steps between 22 and 30 MeV. High-pressure (4)He-Xe gas scintillators of various (4)He/Xe ratios served as targets and detectors. Pure Xe gas scintillators were used for background studies. A NaI detector together with a plastic scintillator paddle was employed for determining the incident photon flux. Our comprehensive data set follows the trend of the theoretical calculations of the Trento group very well, although our data are consistently lower in magnitude by about 5%. However, they differ significantly from the majority of the previous data, especially from the recent data of Shima et al. The latter data had put into question the validity of theoretical approaches used to calculate core-collapse supernova explosions and big-bang nucleosynthesis abundances of certain light nuclei.     

Formation of 8He in the 9Be(π–, p)X and 10B(π–, pp)X Stopped Pion Absorption Reactions

JETP Letters - The structure of levels of the 8He heavy helium isotope has been studied in the 9Be $$({{\pi }^{ - }},p)X$$ and 10B $$({{\pi }^{ - }},pp)X$$ stopped pion absorption reactions....     

Study of the Δ isobar excitation in nuclei with the (3He,t) reaction

Data for the Δ excitation by the (³He,t) reaction at 2.0 GeV on various nuclei are presented together with results on ¹²C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(³He,t) Δ⁺⁺ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.     

Determination of astrophysical ~7Be(p,γ)~8B reaction rates from the ~7Li(d,p)~8Li reaction

The7Be(p,γ)8B reaction plays a central role not only in the evaluation of solar neutrino fluxes but also in the evolution of the first stars.Study of this reaction requires the asymptotic normalization coefficient(ANC) for the virtual decay8 Bg.s.→7Be + p.By using the charge symmetry relation,we obtain this proton ANC with the single neutron ANC of8 Lig.s.→7Li + n,which is determined with the distorted wave Born approximation(DWBA) and adiabatic distorted wave approximation(ADWA) analysis of the7Li(d,p)8Li angular distribution.The astrophysical S-factors and reaction rates of the direct capture process in the7Be(p,γ)8B reaction are further deduced at energies of astrophysical relevance.The astrophysical S-factor at zero energy for direct capture,S17(0),is derived to be(19.9±3.5) e V b in good agreement with the most recent recommended value.The contributions of the1+and 3+resonances to the S-factor and reaction rate are also evaluated.The present result demonstrates that the direct capture dominates the7Be(p,γ)8B reaction in the whole temperature range.This work provides an independent examination to the current results of the7Be(p,γ)8B reaction.     

Extrapolation of theS(E) factor in7Be(p, γ0)8B: the7Li(p, γ0)8Be case

The observed M1 capture amplitude in⁷Li(p,_o)⁸Be At E_p=80–0 keV originates predominantly from the low-energy tail of a resonance at 441 keV, thue removing a recent criticism on the extrapolation of S(E) data such as for⁷Be(p,)⁸B.     

Study of the 4He(e,e′d)pn Reaction

 The cross section for the ⁴He(e,e′d)pn reaction has been measured in parallel and in (q, ω)-constant kinematics for values of the three-momentum transfer of 406, 495 and 595 MeV/c, and for a range in missing momentum. Just above threshold this reaction can be characterized as a spin/isospin flip transition of the involved pn pair. By using two electron energies (576 and 370 MeV) the longitudinal and transverse structure functions could be separated. The cross sections turn out to be purely transverse, as expected for a spin/isospin flip transition. The data are well described by new covariant and current-conserving calculations that include the major final-state interaction effects. Received August 20, 1998; modified October 12, 1998; accepted for publication January 30, 1999