R. J. Livesay

Direct reaction measurements with a 132Sn radioactive ion beam

The (d,p) neutron transfer and (d,d) elastic scattering reactions were measured in inverse kinematics using a radioactive ion beam of {sup 132}Sn at 630 MeV. The elastic scattering data were taken in a region where Rutherford scattering dominated the reaction, and nuclear effects account for less than 8% of the elastic scattering cross section. The magnitude of the nuclear effects, in the angular range studied, was found to be independent of the optical potential used, allowing the transfer data to be normalized in a reliable manner. The neutron-transfer reaction populated a previously unmeasured state at 1363 keV, which is most likely the single-particle 3p{sub 1/2} state expected above the N=82 shell closure. The data were analyzed using finite-range adiabatic-wave calculations and the results compared with the previous analysis using the distorted-wave Born approximation. Angular distributions for the ground and first-excited states are consistent with the previous tentative spin and parity assignments. Spectroscopic factors extracted from the differential cross sections are similar to those found for the one-neutron states beyond the benchmark doubly magic nucleus {sup 208}Pb.

The

The production of 26Al in novae is uncertain, in part, because of the uncertain rate of the 25Al(p,g)26Si reaction at novae temperatures. This reaction is thought to be dominated by a longsought 3+ level in 26Si, and the calculated reaction rate varies by orders of magnitude depending on the energy of this resonance. We present evidence concerning the spin of a level at 5.914 MeV in 26Si from the 28Si(p,t)26Si reaction studied at the Holifield Radioactive Beam Facility at ORNL. We find that the angular distribution for this level implies either a 2+ or 3+ assignment, with only a 3+ being consistent with the mirror nucleus, 26Mg. Additionally, we have used the updated 25Al(p,g)26Si reaction rate in a nova nucleosynthesis calculation and have addressed the effects of the remaining uncertainties in the rate on 26Al production.

^{25}

We have developed a novel technique for measurements of low-energy (p,{alpha}) reactions using heavy-ion beams and a differentially pumped windowless gas target. We applied this new approach to study the 183 keV resonance in the {sup 17}O(p,{alpha}){sup 14}N reaction. We report a (center-of-mass) resonance energy of E{sub r}=183.5(+0.1/-0.4) keV and a resonance strength of {omega}{gamma}{sub p{alpha}}=(1.70{+-}0.15) meV, and we set an upper limit (95% confidence) on the total width of the state of {gamma}<0.1 keV. This resonance is important for the {sup 17}O(p,{alpha}){sup 14}N reaction rate, and we find that {sup 18}F production is significantly decreased in low-mass ONeMg novae but less affected in more energetic novae. We also report the first determination of the stopping power for oxygen ions in hydrogen gas near the peak of the Bragg curve (E=193 keV/u) to be (63{+-}1)x10{sup -15} eV cm{sup 2}.

Al

The 2H(82Ge,p)83Ge and 2H(84Se,p)85Se reactions were studied with radioactive beams of 82Ge and 84Se at beam energies of Ebeam = 330 and 380 MeV, respectively. Excitation energies, proton angular distributions, and asymptotic normalization coefficients have been determined for the lowest lying states of 83Ge and 85Se. Spectroscopic factors have also been extracted under normal assumptions of the bound-state potential properties in the DWBA analysis. However, the peripheral character of the measurements leads to large uncertainties in this extraction. Shell model calculations have been performed in the region above 78Ni, comparing the single-particle properties of the even-Z, N = 51 nuclei up to 91Zr and including 83Ge and 85Se. Direct-semidirect neutron capture calculations to 83Ge and 85Se have also been performed using the spectroscopic input from these (d,p) reaction measurements.

(p,\gamma)^{26}

The 29P(p,gamma)30S rate affects interpretation of nova Si abundances, which have been precisely measured in presolar grains. The rate is thought to be dominated by previously unobserved 3+ and 2+ resonances above the 30S proton threshold at 4400 keV. To better understand the 29P(p,gamma)30S rate, we have studied the 30S nucleus with the 32S(p,t)30S reaction. We have observed 13 30S levels - 9 of which are above the proton threshold including a level at 4704 keV that is a candidate to be the important 3+ resonance. From the observed triton angular distributions, we additionally constrain the spins of several levels. Using our updated information, we estimate the 29P(p,gamma)30S reaction rate is approximately six times larger at nova temperatures than previously thought.

Si Reaction Rate in Novae

The

Measurement of the 183 keV resonance in {sup 17}O(p,{alpha}){sup 14}N using a novel technique

^{28}\mathrm{Si}

Single-neutron excitations in neutron-rich {sup 83}Ge and {sup 85}Se

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{sup 30}S studied with the {sup 32}S(p,t){sup 30}S reaction and the {sup 29}P(p,{gamma}){sup 30}S reaction rate

p,t

Astrophysically important {sup 26}Si states studied with the {sup 28}Si(p,t){sup 26}Si reaction. II. Spin of the 5.914-MeV {sup 26}Si level and galactic {sup 26}Al production

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