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[en] The existence of two systematically inconsistent sets of measurements of the ²⁴Al excitation energies, which are used to determine ²³Mg+p resonance energies, results in a variation of a factor 5 in the thermonuclear ²³Mg(p,γ)²⁴Al reaction rate at T=0.25 GK. The astrophysically important energies have been determined to an uncertainty of 6 keV by measuring triton spectra from the ²⁴Mg(³He,t)²⁴Al reaction at E(³He)=30 MeV, and good general agreement is found with one previous set. The present measurement of E_x=2346(6) keV for what is thought to be the most important resonance is, however, in disagreement with both prior measurements of 2328(10) and 2369(4) keV, where the latter value belongs to the outlying set. The presently determined resonance energies reduce the related uncertainty in the ²³Mg(p,γ)²⁴Al reaction rate by a factor of ≅3, which will constrain the determination of nuclear flow out of the NeNa cycle, and production of A≥20 nuclides, in explosive hydrogen burning over a temperature range 0.2< T<1.0 GK

[en] Using recent data we reduce the systematic uncertainty in our measurement [Phys. Rev. C 76, 065803 (2007)] of the excitation energy of the second level above the proton threshold in ²⁴Al and find it to be 2523(3) keV, a factor of two improvement over our previously reported value of 2524(6) keV

[en] The ²⁹P(p,γ)³⁰S reaction rate affects the 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 4399 keV. To better understand the ²⁹P(p,γ)³⁰S rate, we have studied the ³⁰S nucleus with the ³²S(p,t)³⁰S reaction. We have observed 13 ³⁰S levels, nine of which are above the proton threshold, including a level at 4704 keV that is a candidate to be the important 3⁺ resonance. We also resolve a significant discrepancy between previously published excitation energies. From the observed triton angular distributions, we constrain the spins of several levels, ruling out several previous hypotheses and constraining some for the first time. Using our updated information, we estimate the ²⁹P(p,γ)³⁰S reaction rate is approximately six times larger at nova temperatures than previously thought

[en] Knowledge of the ³He(³He,2p)⁴He reaction is important for understanding stellar burning and solar neutrino production. Previous measurements have found a surprisingly large rise in the cross section at low energies that could be due to a low energy resonance in the ³He+³He (⁶Be) system or electron screening. In the ⁶Be nucleus, however, no excited states have been observed above the first 2⁺ state at Ex = 1.67 MeV up to 23 MeV, even though several are expected. The d(⁷Be,t)⁶Be reaction has been studied for the first time to search for resonances in the ⁶Be nucleus that may affect our understanding of the ³He(³He,2p)⁴He reaction. A 100-MeV ⁷Be beam from the Holifield Radioactive Ion Beam Facility (HRIBF) was used to bombard CD₂ targets, and tritons were detected by the Silicon Detector Array (SIDAR). It appears that a combination of reaction mechanisms is necessary to explain the observed triton energy spectrum

[en] Knowledge of the ³He(³He,2p)⁴He reaction is important for understanding stellar burning and solar neutrino production. Previous measurements have found a surprisingly large rise in the cross section at low energies that could be due to a low energy resonance in the ³He+³He (⁶Be) system or electron screening. In the ⁶Be nucleus, however, no excited states have been observed above the first 2⁺ state at E_x = 1.67 MeV up to 23 MeV, even though several are expected. The d(⁷Be,t)⁶Be reaction has been studied for the first time to search for resonances in the ⁶Be nucleus that may affect our understanding of the ³He(³He,2p)⁴He reaction. A 100-MeV ⁷Be beam from the Holifield Radioactive Ion Beam Facility (HRIBF) was used to bombard CD₂ targets, and tritons were detected by the Silicon Detector Array (SIDAR). It appears that a combination of reaction mechanisms is necessary to explain the observed triton energy spectrum.

[en] The ²H(⁸²Ge,p)⁸³Ge and ²H(⁸⁴Se,p)⁸⁵Se reactions were studied with radioactive beams of ⁸²Ge and ⁸⁴Se at beam energies of E_beam=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 distorted waves Born approximation 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

[en] The ²⁸Si(p,t)²⁶Si reaction has been studied to resolve a controversy surrounding the properties of the ²⁶Si level at 5.914 MeV and its contribution to the ²⁵Al(p,γ)²⁶Si reaction rate in novae, which affects interpretations of galactic ²⁶Al observations. Recent studies have come to contradictory conclusions regarding the spin of this level (0⁺ or 3⁺), with a 3⁺ assignment implying a large contribution by this level to the ²⁵Al(p,γ)²⁶Si reaction rate. We have extended our previous study [Bardayan et al., Phys. Rev. C 65, 032801(R) (2002)] to smaller angles and find the angular distribution of tritons populating the 5.914-MeV level in the ²⁸Si(p,t)²⁶Si reaction to be consistent with either a 2⁺ or 3⁺ assignment. We have calculated reaction rates under these assumptions and used them in a nova nucleosynthesis model to examine the effects of the remaining uncertainties in the ²⁵Al(p,γ)²⁶Si rate on ²⁶Al production in novae