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.     

Determination of the ~(12)C(p, γ)~(13)N reaction rates fromthe ~(12)C(~7Li,~6He)~(13)N reaction

The angular distribution of the 12C(7Li,6He)13N reaction at E(7Li) = 44.0 MeV was measured at the HI-13 tandem accelerator of Beijing, China. The asymptotic normalization coefficient (ANC) of 13N → 12C + p was derived to be (1.64 ± 0.11) fm-1/2 through the distorted wave Born approximation (DWBA) analysis. The ANC was then used to deduce the astrophysical S (E) factors and reaction rates for the 12C(p,γ)13N direct capture reaction at energies of astrophysical relevance.     

Comment on the7Li(p, γ)8Be reaction at energies of astrophysical interest

The results of two recent publication are reconsidered. These papers argue that the p-wave effects seen in the⁷ Li(p, ) ⁸ Be reaction belowE _p=80 keV can be accounted for by considering the low-energy tail of the p-wave resonance atE _p=441 keV. It is shown that the cross section and analyzing power data require an order-of-magnitude more p-wave strength when considered together.This work was supported by the U.S. Department of Energy, Office of High Energy and Nuclear Physics, under Contract No. DEFG05-91-ER40619.     

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.     

New determination of astrophysical14C（n, γ）15C reaction rate from the spectroscopic factor of 15C

The14C(n,γ)15C reaction plays an important role in various astrophysical scenarios:(1)it is the slowest in the neutron induced CNO cycle which occurs in asymptotic giant branch(AGB)stars,and therefore controls this cycle[1];(2)it is one of the key reactions for predicting the primordial abundances of the heavy elements in the framework of inhomogeneous big-bang nucleosynthesis(IBBN)[2];(3)it is also important for the synthesis of heavier isotopes in neutrino driven wind scenarios for the r-process in core-collapse supernova(i.e.,Type-II supernova)explosions[3-5].     

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.     

Measuring the astrophysical S factors and the cross sections of the p(d, γ)3He reaction in the ultralow energy region using a zirconium deuteride target

The present paper is dedicated to the study of the p(d, γ)³He reaction mechanism with the use of a zirconium deuteride target at proton energies of 11–19 keV. The experiment has been carried out using a proton beam of a high-current pulsed Hall accelerator at the National Research Tomsk Polytechnic University. The dependences of the astrophysical S factor and the effective cross section of the pd reaction on the proton-deuteron collision energy are measured. The results were compared with the available data. The results detailed in the present work agree with the results of an experiment carried out by the LUNA collaboration with the use of a gaseous deuterium target.     

The S(E) factor of7Li(p, γ)8Be and consequences for S(E) extrapolation in7Be(p, γ0)8B

Excitation functions and forward-backward anisotropies have been measured for the⁷Li(p, )⁸Be capture reaction over the proton energy rangeE _p =100 to 1500 keV, using a 4 summing crystal and Ge(Li) detectors, respectively. The data show at all energies the presence of El and M1 capture amplitudes arising from the direct capture (DC) process and theE _R =441 and 1030 keV resonances, respectively. Due to the observed DC process, the present data increase significantly the reaction rates (up to a factor of 110) compared to values given in the compilation. The data and their analyses remove the recent criticism on DC model calculations, which had implied a significant reduction in the extrapolated S(E) factor for⁷Be(p,)B and thus in the predicted flux of high-energy solar neutrinos; thus, the solar neutrino problem is still with us.Supported in part by the Deutsche Forschungsgemeinschaft (Ro429/21-3 and Ro429/21-4) and the German-Hungarian Collaboration (X238.6 and OTKA3808)     

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.     

New measurement of thick target yield for narrow resonance at E_x= 9.17 MeV in the ~(13)C(p, γ)~(14)N reaction

High energy γ-rays can be used in many fields, such as nuclear waste transmutation, flash photographics, and astrophysics. The~(13) C(p, γ)~(14) N resonance reaction was used to generate high energy and mono-energetic γ-rays in this work. The thick-target yield of the 9.17-MeV γ-ray from the resonance in this reaction was determined to be(4.7±0.4)×10~(-9)γ/proton,which was measured by a HPGe detector. Meanwhile, the angular distribution of 9.17-MeV γ-ray was also determined.The absolute efficiency of HPGe detector was calibrated using~(56 )Co and~(152) Eu sources with known radioactive activities and calculated by GEANT4 simulation.     

Breakup of 8B and the 7Be(p, γ)8B reaction

The calculated rate of events in some of the existing solar neutrino detectors is directly proportional to the rate of the ⁷Be(p, γ)⁸B reaction measured in the laboratory at low energies. However, the low-energy cross sections of this reaction are quite uncertain as various measurements differ from each other by 30–40%. The Coulomb dissociation process which reverses the radiative capture by the dissociation of ⁸B in the Coulomb field of a target, provides an alternate way of accessing this reaction. While this method has several advantages (like large breakup cross sections and flexibility in the kinematics), the difficulties arise from the possible interference by the nuclear interactions, uncertainties in the contributions of the various multipoles and the higher order effects, which should be considered carefully. We review the progress made so far in the experimental measurements and theoretical analysis of the breakup of ⁸B and discuss the current status of the low-energy cross sections (or the astrophysical S-factor) of the ⁷Be(p, γ)⁸B reaction extracted therefrom. The future directions of the experimental and theoretical investigations are also suggested. Work supported by EPSRC, UK, grant nos J/95867 and L/94574.     

Study of the 13N(p, γ)14O reaction at stellar energies in a microscopic coupled-channel approach

We have studied the ¹³N(p, γ)¹⁴O reaction at stellar energies within a microscopic coupled channel approach based on the generator coordinate method. Our calculation improves previous investigations as we explicitly take into account the internal excitation of the ¹³N fragment nucleus. We find that the cross section at stellar energies is mainly dominated by the J^π = 1⁻ resonance at E = 0.547 MeV in ¹⁴O for which we calculate a γ-width of Γ_γ = 1.6 eV. For temperatures T = 10⁸ to 10⁹ K the thermally averaged ¹³N(p, γ)¹⁴O reaction rate is also sensitive to a direct capture contribution which we derive consistently within our microscopic study. Finally we discuss the astrophysical implications of the ¹³N(p, γ)¹⁴O rate for which we adopt a mean value of the various theoretical estimates of the γ-width of the 1⁻ resonance (Γ_γ = 1.8 eV).     

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.     

A study of the reaction (π+, π+ p) in 12C and 6Li

We have measured the angular and momentum distributions of the scattered pions from the reaction ¹²C(π⁺, π⁺p)¹¹B and ⁶Li(π⁺, π⁺ p)⁵He in a coincidence experiment. We compare our results with the plane and distorted wave impulse approximations.     

Measurement of the astrophysical S factor for the low energy 2H(d,γ)4He reaction

The y-rays and protons from an Ed = 20 keV deuteron beam incident on a D-Ti target were measured. A branching ratio of the 2H(d,T)4He reaction versus the 2H(d,p)aH reaction of F.v/l'p = (1.06+ 0.34) x 10-7 has been obtained, and the astrophysical S factor of the 2H(d,T)aHe reaction at the center of mass energy Ecru ≈ 7 keV of (6.0+2.4) x 10-8 keV.b was deduced.     

Quasi-free processes in 6Li(3He,pα)4He reaction at low energies

The ⁶Li(³He, pα)⁴He reaction was studied experimentally at 3.5, 4.4 and 5.5 MeV in the quasi-free reaction kinematical region. The effects of a resonance in the virtual ²H(³He, p)⁴He reaction on the three-body reaction cross section were investigated.     

Location of multiparticle-multihole strength in 16N via the 3-particle transfer reaction 13C(α, p)16N at 118 MeV

Differential cross sections were measured for the ¹³C(α, p)¹⁶N reaction at E_α = 118 MeV for an excitation energy range up to 14.5 MeV. Zero-range distorted wave Born approximation (DWBA) calculations were performed using microscopic form factors. Spin-parity assignments are suggested for states at 11.21 MeV (6⁻) and 11.81 MeV (7⁻) on the basis of Bansal-French-Zamick weak coupling calculations and DWBA calculations. Arguments from ¹⁶O(e, e'), ¹⁶O(p, p') and the present experiment are given relating to the location of J^π = 4⁻, T = 1 strength in ¹⁶N.