[en] Knowledge of the ¹⁷F(p,γ)¹⁸Ne reaction rate is important for understanding stellar explosions, but it was uncertain because the properties of an expected but previously unobserved 3⁺ state in ¹⁸Ne were not known. This state would provide a strong s-wave resonance for the ¹⁷F+p system and, depending on its excitation energy, could dominate the stellar reaction rate at temperatures above 0.2 GK. We have observed this missing 3⁺ state by measuring the ¹H(¹⁷F,p)¹⁷F excitation function with a radioactive ¹⁷F beam at the ORNL Holifield Radioactive Ion Beam Facility (HRIBF). We find that the state lies at a center-of-mass energy of E_r=599.8±1.5_stat±2.0_sys keV (E_x=4523.7±2.9keV) and has a width of Γ=18±2_stat±1_syskeV. The measured properties of the resonance are only consistent with a J^π=3⁺ assignment

[en] The lowest-energy resonance in the ²³Mg(p,γ)²⁴Al reaction, which is dominant at classical nova temperatures, has been measured directly for the first time using the DRAGON recoil spectrometer. The experiment used a radioactive ²³Mg beam (mixed within a significantly stronger ²³Na beam) of peak intensity 5x10⁷ s^-1, at the ISAC facility at TRIUMF. We extract values of E_R=485.7_-1.8^+1.3 keV and ωγ=38_-15⁺²¹ meV from our data (all values in the center-of-mass frame unless otherwise stated). In addition, the experiment prompted a recalculation of the Q value for this reaction based on a revision of the ²⁴Al mass. The effect on the uncertainties in the quantities of ejected ²²Na and ²⁶Al from oxygen-neon classical novae is discussed.

[en] Radiative α-particle capture into the first excited, J^π=0⁺ state of ¹⁶O at 6.049 MeV excitation energy has rarely been discussed as contributing to the ¹²C(α,γ)¹⁶O reaction cross section due to experimental difficulties in observing this transition. We report here measurements of this radiative capture in ¹²C(α,γ)¹⁶O for center-of-mass energies of E=2.22 MeV to 5.42 MeV at the DRAGON recoil separator. To determine cross sections, the acceptance of the recoil separator has been simulated in GEANT as well as measured directly. The transition strength between resonances has been identified in R-matrix fits as resulting both from E2 contributions as well as E1 radiative capture. Details of the extrapolation of the total cross section to low energies are then discussed [S_6.0(300)=25_-15⁺¹⁶ keV b] showing that this transition is likely the most important cascade contribution for ¹²C(α,γ)¹⁶O

[en] A small fraction (< 1%) of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The ²⁹P(p,γ)³⁰S reaction plays an important role in understanding the Si isotopic abundances in such grains, which in turn provide us with information on the nature of the probable white dwarf progenitor's core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. This rate at nova temperatures is determined by two low-lying 3⁺ and 2⁺ resonances above the proton threshold at 4399 keV in ³⁰S. Despite several experimental studies in the past, however, these two states have only been observed very recently. We have studied the ³⁰S nuclear structure via the ³²S(p,t)³⁰S reaction at 5 laboratory angles between 9⁰ to 62⁰. We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7 ± 4.5 keV and 4813.8 ± 3.4 keV that are candidates for the 3⁺ and the previously 'missing' 2⁺ state, respectively.

[en] The ²⁹P(p,γ)³⁰S reaction plays an important role in understanding the Si isotopic abundances in presolar grains of nova origin, which in turn provide us with information on the nature of the probable white dwarf progenitor's core, as well as the peak temperatures achieved during nova outbursts. This rate at nova temperatures is determined by two low-lying 3⁺ and 2⁺ resonances above the proton threshold at 4399 keV in ³⁰S. We have studied the ³⁰S nuclear structure via the ³²S(p,t)³⁰S reaction at 5 laboratory angles between 9 deg. to 62 deg. We have observed 14 states including two levels at 4692.7±4.5keV and 4813.8±3.4keV that are candidates for the 3⁺ and the previously 'missing'2⁺ state, respectively.

[en] The short-lived nuclide ⁴⁴Ti is an important nuclide for the understanding of explosive nucleosynthesis. The main production reaction, ⁴⁰Ca(α,γ)⁴⁴Ti, has been studied in inverse kinematics with the recoil mass spectrometer DRAGON located at the TRIUMF-ISAC facility in Vancouver, Canada. The temperature range relevant for α-rich freeze-out during a core-collapse supernova has been covered entirely with a ⁴⁰Ca beam of 0.60 to 1.15 MeV/nucleon. All relevant quantities for the calculation of the astrophysical reaction rate have been measured directly. Because of many previously undiscovered resonances, the reaction rate derived from the energy dependent ⁴⁴Ti yield is higher than the one based on previous prompt γ-ray studies commonly used in supernova models. The presented new rate results in an increased ⁴⁴Ti production in supernovae

[en] A small fraction of presolar SiC grains is suggested to have been formed in the ejecta of classical novae. The Si isotopic abundances in such grains can be determined from the ²⁹P(p,γ)³⁰S reaction rate at nova temperatures. The Si isotopic abundances provide us with information on the nature of the probable white dwarf progenitor's core, as well as the peak temperatures achieved during nova outbursts, and thus the nova nucleosynthetic path. The ²⁹P(p,γ)³⁰S reaction rate at nova temperatures is determined by two low-lying 3⁺ and 2⁺ resonances above the proton threshold at 4399 keV in ³⁰S. However, only one of these two states has only been observed very recently. We have studied the ³⁰S nuclear structure via the ³²S(p,t)³⁰S reaction at 5 laboratory angles between 9 deg. to 62 deg. . We have observed 14 states, eleven of which are above the proton threshold, including two levels at 4692.7±4.5 keV and 4813.8±3.4 keV that are candidates for the 3⁺ and the previously ''missing''2⁺ state, respectively.

[en] 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 E_x= 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 J^π 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.

[en] Over the past three years, we have worked on developing a well-characterized ³⁰S radioactive beam to be used in a future experiment aiming to directly measure to extrapolate the ³⁰S(α,p) stellar reaction rate within the Gamow window of Type I X-ray bursts. The importance of the ³⁰S(α,p) reaction to X-ray bursts is discussed. Given the astrophysical motivation, the successful results of and challenges involved in the production of a low-energy ³⁰S beam are detailed. Finally, an overview of our future plans regarding this on-going project are presented.

[en] Type I X-ray bursts are the most common explosions in the Galaxy; however, the nucleosynthesis that occurs during the thermonuclear runaway and explosion is poorly understood. In this proceedings we discuss current experimental efforts and techniques that are being used to study X-ray burst nucleosynthesis in the laboratory. Specifically, radioactive ion beam techniques that have recently been developed have allowed the study of some of the most important (α, p) reactions in X-ray bursts for the first time.