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Background: The uncertainty in the 29P(p, ɣ )30S reaction rate over 0.1 ≤ T ≤ 1.3GK was previously determined to span approximately four orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the Ex = 4.7-4.8 MeV region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. Purpose: (a) To investigate the level structure of 30S above the proton threshold [4394.9(7) keV] via chargedparticle spectroscopy using the 32S(p, t)30S reaction and in-beam y-ray spectroscopy using the 28Si(³He, ny)30S reaction to calculate the 29P(p, ɣ)30S reaction rate, (b) To explore the impact of this rate on the abundances of silicon isotopes synthesized in novae. Methods: Differential cross sections of the 32S(p, t)30S reaction were measured at 34.5 MeV. Distorted-wave Bom approximation calculations were performed to constrain the spin-parity assignments of the observed levels, including the two astrophysically important levels. An energy-level scheme was deduced from ɣ-ɣ coincidence measurements using the 28Si(³He, nɣ)30S reaction. Spin-parity assignments based on measurements of ɣ-ray angular distributions and ɣ-ɣ directional correlation from oriented nuclei were made for most of the observed levels of 30S. Results: The resonance energies corresponding to the states with 4.5 MeV ≤ Ex ≤ 6 MeV, ncluding the two astrophysically important states predicted previously, are measured with significantly better precision than before. The spin-parity assignments of both astrophysically important resonances are confirmed. The uncertainty in the rate of the 29P(p, ɣ)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via ID hydrodynamic nova simulations. Conclusions: The uncertainty in the 29P(p, ɣ)30S reaction rate is reduced to the point that it no longer affects the silicon isotopic abundance ratios significantly, and, thus, the results of our nova hydrodynamic simulation for the nucleosynthesis in the Si-Ca mass region are more reliable than before. [ABSTRACT FROM AUTHOR]

The structure of proton-unbound 30S states strongly determines the thermonuclear 29P(p,γ)30S reaction rate at temperatures characteristic of explosive hydrogen burning in classical novae and type I x-ray bursts. Specifically, the rate had been previously predicted to be dominated by two low-lying, unobserved, levels in the Ex= 4.7-4.8 MeV region, with spin and parity assignments of 3+ and 2+. In recent experimental work, two candidate levels were observed with energies of 4.699 MeV and 4.814 MeV, but no experimental information on their spins and parities was obtained. We have performed an in-beam γ-ray spectroscopy study of 30S with the 28Si(3He, nγ)30S reaction. By constructing the decay schemes of proton-unbound states with a γ-γ coincidence analysis of their decay γ rays, their Jπ values were inferred from a comparison to the known decay schemes of the corresponding mirror states in 30Si. For the two aforementioned states, our results strongly corroborate the spin-parity assignments assumed in recent evaluations of the 29P(p,γ)30S reaction rate. [ABSTRACT FROM AUTHOR]

Proton-unbound excited states of 31S have been populated with the 32S(d, t)31 S reaction at a beam energy of 24 MeV. Tritons corresponding to 31S states with EX(31,S) ≈ 6.3-7.1 MeV were momentum analyzed with a high resolution quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph at six angles ranging from (θlab = 15°to 58.5°. We report a statistically significant detection of an astrophysically important state at EX(31 S) = 6402 (2) keV, whose existence as a third state in this region has been under debate. Using updated A = 31 nuclear structure information, we present a new set of proposed 31S-31P mirror assignments for 31S, in which this state is tentatively assigned a spin of 7/2. This level, corresponding to a 30P + p resonance at 271 keV, is likely to have a significant influence on the 30P(p, γ)31 reaction rate in explosive hydrogen burning in classical novae. [ABSTRACT FROM AUTHOR]

The 17O(p,γ)18F reaction plays an important role in hydrogen-burning nucleosynthesis. Conflicting values for the low-energy behavior of its cross section exist in the literature. We present direct measurements of the astrophysical S factor of the 17O(p,γ)18F reaction at center-of-mass energies between 250 and 500 keV. These measurements were conducted in inverse kinematics at the DRAGON recoil separator. [ABSTRACT FROM AUTHOR]

Model predictions of the amount of the radioisotope 26A1 produced in hydrogen-burning environments require reliable estimates of the thermonuclear rates for the 26gAl(p,γ) 27Si and 26mAl(p,γ)27Si reactions. These rates depend upon the spectroscopic properties of states in 27Si within about 1 MeV of the 26sAl + p threshold (Sp = 7463 keV). We have studied the 28Si(3He,α)27Si reaction at 25 MeV using a high-resolution quadrupole-dipole-dipole-dipole magnetic spectrograph. For the first time with a transfer reaction, we have constrained Jπ values for states in 27Si over Ex = 7.0-8.1 MeV through angular distribution measurements. Aside from a few important cases, we generally confirm the energies and spin-parity assignments reported in a recent γ-ray spectroscopy study. The magnitudes of neutron spectroscopic factors determined from shell-model calculations are in reasonable agreement with our experimental values extracted using this reaction. [ABSTRACT FROM AUTHOR]