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All the 16F levels are unbound by proton emission. To date the four low-lying 16F levels below 1 MeV have been experimentally identified with well established spin-parity values and excitation energies with an accuracy of 4 - 6 keV. However, there are still considerable discrepancies in their level widths. The present work aims to explore these level widths through an independent method. The angular distributions of the 15N(7Li,6Li)16N reaction leading to the first four states in 16N were measured using a high-precision Q3D magnetic spectrograph. The neutron spectroscopic factors and the asymptotic normalization coefficients for these states in 16N were then derived based on distorted wave Born approximation analysis. The proton widths of the four low-lying resonant states in 16F were obtained according to charge symmetry of strong interaction. [ABSTRACT FROM AUTHOR]

Background: Fluorine is a key element for nucleosynthetic studies since it is extremely sensitive to the physical conditions within stars. The astrophysical site to produce fluorine is suggested to be asymptotic giant branch stars. In these stars the 15N(n,γ)16N reaction could affect the abundance of fluorine by competing with 15N(α,γ)F19. Purpose: The 15N(n,γ)16N reaction rate depends directly on the neutron spectroscopic factors of the low-lying states in 16N. Shell model calculations and two previous measurements of the (d,p) reaction yielded the spectroscopic factors with a discrepancy by a factor of ~2. The present work aims to explore these neutron spectroscopic factors through an independent transfer reaction and to determine the stellar rate of the 15N(n,γ)16N reaction. Methods: The angular distributions of the 15N(Li7,Li6)16N reaction populating the ground state and the first three excited states in 16N are measured using a Q3D magnetic spectrograph and are used to derive the spectroscopic factors of these states based on distorted wave Born approximation analysis. Results: The spectroscopic factors of these four states are extracted to be 0.96 ± 0.09, 0.69 ± 0.09, 0.84 ± 0.08, and 0.65 ± 0.08, respectively. Based on the new spectroscopic factors we derive the 15N(n,γ)16N reaction rate. Conclusions: The accuracy and precision of the spectroscopic factors are enhanced due to the first application of high-precision magnetic spectrograph for resolving the closely spaced 16N levels which cannot be achieved in most recent measurements. The present result demonstrates that two levels corresponding to neutron transfers to the 2s1/2 orbit in 16N are not good single-particle levels although 15N is a closed neutron-shell nucleus. This finding is contrary to the shell model expectation. The present work also provides an independent examination to shed some light on the existing discrepancies in the spectroscopic factors and the 15N(n,γ)16N rate. [ABSTRACT FROM AUTHOR]

The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The 12N(p, γ)130 reaction is an important branching point in the rap processes, which are believed to be alternative paths to the slow 3a process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the 2H(12N, 130)n proton transfer reaction at Ec.m. = 8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of 13Og s. --> 12N 4- p was extracted to be 3.92 ± 1.47 fm-' from the measured angular distribution and utilized to compute the direct component in the 12N(p, γ)130 reaction. The direct astrophysical S factor at zero energy was then found to be 0.39 ±0.15 keV b. By considering the direct capture into the ground state of 130, the resonant capture via the first excited state of 130 and their interference, we determined the total astrophysical S factors and rates of the 12N(p, γ130 reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that 12N(p, γ)130 will only compete successfully with the ß+ decay of 12N at higher (~2 orders of magnitude) densities than initially predicted. [ABSTRACT FROM AUTHOR]

The C(Li, He) N reactions were measured at E (Li) = 34 MeV with the Q3D magnetic spectrometer of the HI-13 tandem accelerator, and the first peaks of the angular distributions were obtained for the first time. The N proton spectroscopic factors were extracted to be 0.67±0.09 and 0.73±0.10 , respectively. Using the C( p, γ) N direct capture S( E) factors derived by the spectroscopic factors, the direct measurement data for both 1 and 0 resonances were well fitted via updating the resonance parameters, and then the total astrophysical C( p, γ) N S( E) factors and reaction rates were determined at stellar energies. The present work offers an independent examination to the existing results of the C( p, γ) N reaction. [ABSTRACT FROM AUTHOR]

The angular distribution of the 2H ( 6He,7Li n reaction was measured with a secondary 6He beam of 36.4MeV for the first time. The proton spectroscopic factor of 7Li ground state was extracted to be 0.42±0.06 by normalizing the calculational differential cross-sections with the distorted-wave Born approximation to the experimental data. It was discussed that the uncertainty of extracted spectroscopic factors from the one-nucleon transfer reactions induced by deuteron might be reduced by determining the volume integrals of imaginary optical potentials precisely. [ABSTRACT FROM AUTHOR]

The 74Ge(p , γ)75As reaction is believed to have a strong effect on the production of the lightest p -nucleus 74Se. The 74Ge(p , γ)75As reaction cross sections were measured in the range of E p = 2.5-4.3 MeV with an in-beam γ spectroscopy method at the 3 MV tandem accelerator of the Institute of Nuclear Science and Technology, Sichuan University. The experimental results show good agreement with previous works, and extend the measurements to the widest energies to date combined with our latest work at the 1.7 MV tandem accelerator of China Institute of Atomic Energy. Our new cross sections are compared with theoretical predictions using the TALYS and EMPIRE nuclear reaction codes. The EMPIRE-EGSM calculation presents the best description of all the experimental data, and was used to derive the reaction rates. The present rates are significantly higher than the REACLIB compilation by a factor of up to 47% within the p -process relevant temperatures. [ABSTRACT FROM AUTHOR]

The 12C(α,γ)16O reaction is one of the most crucial reactions in nuclear astrophysics. The E2 external capture to the 16O ground state (GS) has not been emphasized in previous analyses but may make a significant contribution to the 12C(α,γ)16O cross section depending on the value of the GS asymptotic normalization coefficient (ANC). In the present work, we determine this ANC to be 337±45 fm-1/2 through the 12C(11B,7Li)16O reaction using a high-precision magnetic spectrograph. This sheds light on the existing large discrepancy of more than 2 orders of magnitude between the previously reported ANC values. Based on the new ANC, we experimentally constrain the GS external capture and show that through interference with the high energy tail of the 2+ subthreshold state, a substantial enhancement in the GS SE2(300) factor can be obtained (70±7 keV b) compared to that of a recent review (45 keV b), resulting in an increase of the total S factor from 140 to 162 keV b, which is now in good agreement with the value obtained by reproducing supernova nucleosynthesis calculations with the solar-system abundances. This work emphasizes that the external capture contribution for the ground state transition cannot be neglected in future analyses of the 12C(α,γ)16O reaction. [ABSTRACT FROM AUTHOR]

The 74Ge(p , γ)75As reaction plays a crucial role in producing the lightest p -nucleus 74Se. In this work, we present the measurement of the 74Ge(p , γ)75As cross sections in the range of E p = 1.4-2.8 MeV with an in-beam method at the tandem accelerator of China Institute of Atomic Energy. The present result is in good agreement with the previous experiments at higher energies, and extends the measurement down to lower energies of astrophysical interest. Theoretical calculations are also performed using the EMPIRE nuclear reaction code and well reproduce all experimental cross sections, which shed some light on the existing discrepancy in the previously reported experimental and theoretical values at the lowest energies. The resulting reaction rates exhibit a considerable increase of up to 47% within the p -process relevant temperatures when comparing with the REACLIB compilation. [ABSTRACT FROM AUTHOR]

The 18Ne(α,p)21Na reaction is thought to be one of the key breakout reactions from the hot CNO cycles to the rp process in type I x-ray bursts. In this work, the resonant properties of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na + p. An 89-MeV 21Na radioactive beam delivered from the CNS Radioactive Ion Beam Separator bombarded an 8.8 mg/cm² thick polyethylene (CH2)n target. The 21Na beam intensity was about 2 × 105 pps, with a purity of about 70% on target. The recoiled protons were measured at the center-of-mass scattering angles of θc.m. ≈ 175.2°, 152.2°, and 150.5° by three sets of ΔE-E telescopes, respectively. The excitation function was obtained with the thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. In total, 23 states above the proton-threshold in 22Mg were observed, and their resonant parameters were determined via an R-matrix analysis of the excitation functions. We have made several new Jα assignments and confirmed some tentative assignments made in previous work. The thermonuclear 18Ne(α,p)21Na rate has been recalculated based on our recommended spin-parity assignments. The astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(α,p)21Na rate significantly affects the peak nuclear energy generation rate, reaction fluxes, and onset temperature of this breakout reaction in these astrophysical phenomena. [ABSTRACT FROM AUTHOR]

The 1S(p,γ)34Cl reaction is important for constraining predictions of certain isotopic abundances in oxygen-neon novae. Models currently predict as much as 150 times the solar abundance of 33S in oxygen-neon nova ejecta. This overproduction factor may, however, vary by orders of magnitude due to uncertainties in the 33S(p,γ)34Cl reaction rate at nova peak temperatures. Depending on this rate, 33S could potentially be used as a diagnostic tool for classifying certain types of presolar grains. Better knowledge of the 33S(p,γ)34Cl rate would also aid in interpreting nova observations over the S-Ca mass region and contribute to the firm establishment of the maximum endpoint of nova nucleosynthesis. Additionally, the total S elemental abundance which is affected by this reaction has been proposed as a thermometer to study the peak temperatures of novae. Previously, the 33S(p,γ)34Cl reaction rate had only been studied directly down to resonance energies of 432 keV. However, for nova peak temperatures of 0.2-0.4 GK there are 7 known states in 34Cl both below the 432 keV resonance and within the Gamow window that could play a dominant role. Direct measurements of the resonance strengths of these states were performed using the DRAGON recoil separator at TRIUMF. Additionally two new states within this energy region are reported. Several hydrodynamic simulations have been performed, using all available experimental information for the 33S(p,γ)34Cl rate, to explore the impact of the remaining uncertainty in this rate on nucleosynthesis in nova explosions. These calculations give a range of ~ 20-150 for the expected 33S overproduction factor, and a range of ~ 100-450 for the 32S/33S ratio expected in ONe novae. [ABSTRACT FROM AUTHOR]

The 18Ne(a,p)21Na reaction provides a pathway for breakout from the hot CNO cycles to the rp process in type-I x-ray bursts. To better determine this astrophysical reaction rate, the resonance parameters of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na+p. An 89 MeV 21Na radioactive ion beam was produced at the CNS Radioactive Ion Beam Separator and bombarded an 8.8 mg/cm2 thick polyethylene target. The recoiled protons were measured at scattering angles of θc.m.~175° and 152¯ by three θE-E silicon telescopes. The excitation function was obtained with a thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. The resonance parameters have been determined through an R-matrix analysis. For the first time, the Jπ values for ten states above the a threshold in 22Mg have been experimentally determined in a single consistent measurement. We have made three new Jπ assignments and confirmed seven of the ten tentative assignments in the previous work. The 18Ne(a,p)21Na reaction rate has been recalculated, and the astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(a,p)21Na rate significantly affects the peak nuclear energy generation rate and the onset temperature of this breakout reaction in these phenomena. [ABSTRACT FROM AUTHOR]

Abstract: Angular distributions of 2H(6He,7Li)n and 12C(7Li,6He)13N reactions were measured at the HI-13 tandem accelerator, Beijing. Asymptotic normalization coefficient (ANC) of 13N →12C + p was derived to be through distorted wave Born approximation (DWBA) analysis, which was then used to deduce the astrophysical S(E) factors for direct capture in 12C(p,γ)13N at energies of astrophysical relevance. [Copyright &y& Elsevier]

Abstract: Systematic studies of nuclear astrophysical reactions induced by lithium isotopes using the unstable ion beam facility GIRAFFE in CIAE were performed. We have measured the angular distributions of some single nucleon transfer reactions, such as 8Li(d,p)9Li, 8Li(d,n)9Be and 8Li(p,d)7Li in inverse kinematics, and derived the astrophysical S-factors or reaction rates for 8Li(n,γ)9Li and 8Li(p,γ)9Be by using asymptotic normalization coefficient (ANC) or spectroscopic factor. [Copyright &y& Elsevier]