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Complete γ-decay in the 12C(12C,γ)24Mg and 12C(16O,γ)28Si reactions has been measured at energies close to the Coulomb Barrier using the DRAGON spectrometer and its associated BGO γ-array at the TRIUMF facility. The experimental data show an important feeding of doorway states around 10-11 MeV in both reactions. Comparisons with simulations allow to extract the full capture cross section and the main spin involved in the process. Different models are confronted to the results : completely statistical, semi-statistical with an unique entrance spin and cluster. The resolution of the BGO enables to eliminate a fully statistical scenario but is not enough to disentangle the two remaining scenarii. It is shown that the future PARIS array composed of the recently developed LaBr3 scintillators will have capabilities to distinguish between these two scenarii. [ABSTRACT FROM AUTHOR]

The radiative capture process of the 12C+12C and 12C+16O reactions has been studied using the very selective 0° Dragon spectrometer at Triumf and its associated BGO γ-array. The experiments have been performed at energies around the Coulomb barrier where resonances in the process have been reported. Our results show previously unobserved γ-decay to doorway states in the 24Mg and 28Si respectively around 10 to 12 MeV. The nature of the states is discussed and two scenarii are proposed. [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]

In stars, 16O represents the endpoint of the helium burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total cross section of 16O(α,γ)20Ne at Ec.m. = 1.69 MeV employing the DRAGON recoil separator. In addition, the branching ratios and strength of the Ec.m. = 2.426 MeV 3- resonance were determined. [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]

Abstract: The Nuclear Astrophysics program at TRIUMF, particular the one centered around the DRAGON and TUDA facilities, as well as some additional experiments will be discussed. In particular, measurements of the 12C(α,γ)16O, the 26Al(p,γ)27Si and the 40Ca(α,γ)44Ti reactions at DRAGON will be described. For the TUDA facility a measurement of 10B(α,p)13C as a test for the 18Ne(α,p)21Na measurement is presented. The development of the new cylindrical, large solid angle gas detector TACTIC will be described. In addition, new measurements refuting a temperature dependence of radioactive decay times in metals will be presented as well as GEANT4 simulations regarding the β-delayed α-spectrum of 16N will be given. [Copyright &y& Elsevier]

Resonant scattering studies were performed using radioactive 20,21Na beams at ISAC between energies of 0.5 keV/u and 1.5 keV/u. Intensities of up to 1 × 108 /sec were used with thick CH2 targets, and elastic and inelastic proton resonances were observed corresponding to states in 21,22Mg by detecting recoil protons using the LEDA silicon array. A multichannel R-Matrix formalism was used to fit the excitation functions leading to the deduction of partial widths and spin-parity assignments. In certain cases definite spin-parity assignments could be made without fitting angular distributions due to the constraining nature of Coulomb-interfering resonances. Where possible, analogue assignments are made in the A=22, T=1, system based on the 21Na+p analysis. [Copyright &y& Elsevier]