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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]

The reaction paths of two proposed nucleosynthetic processes on the proton-rich side of stability, the r p and vp processes, pass through a region of isotopes between Mo and Pd where masses had long gone unmeasured. Precise knowledge of the paths and final abundances of these two processes has been limited by the corresponding lack of precision in the proton-separation energies Sp, when derived from extrapolated masses. The masses of 18 neutron-deficient isotopes of Nb, Mo, Tc, Ru, and Rh have been measured using the Canadian Penning trap mass spectrometer. Three of the masses presented, 90Mo, 91Mo, and 93Tc, provide the first direct measurement of the masses of these nuclides, and the others provide confirmation of recent measurements using other Penning traps. Included in this work is a measurement of the mass of 87Mo, which differs by 3.7σ from the mass presented in the 2003 Atomic Mass Evaluation. This leads to a change in the Sp, value of 88Tc which reduces the suppression of flow of the vp-process path through 87Mo(p, γ)88Tc reported following the mass measurement of 88Tc [C. Weber et al.. Phys. Rev. C 78, 054310 (2008)]. This in turn affects the resulting vp-process abundances. [ABSTRACT FROM AUTHOR]

The heavy-ion radiative capture 12C(O16,γ28Si) was measured at the sub-Coulomb barrier bombarding energy Elab = 15.7 MeV, which corresponds to the lowest important resonance observed in the 12C+ O16 fusion excitation function. Thanks to combination of the bismuth germanate (BGO) γ-ray array and the 0° DRAGON electromagnetic spectrometer at TRIUMF, the γ-decay spectrum from the entrance channel down to the ground state of 28Si was measured. Comparisons of the experimental spectrum to γ spectrum extracted from Monte Carlo simulations of the complete setup suggest a Jπ = 2+ spin-parity assignment to the entrance channel and yield the radiative capture cross section ωRC = 0.22±0.04μb. Combining this present spin assignment with previous data on radiative capture, a J(J+1) systematics was constructed, and it indicated a moment of inertia commensurate with the 12C+O16 grazing angular momentum. Strong dipole transitions are observed from the entrance channel to T=1 states around 11.5 MeV and are found to result from enhanced M1IV transitions to states exhausting a large part of the M1 sum rule built on the ground state of 28Si. This specific decay was also reported at bombarding energies close to the Coulomb barrier in our previous study of the 12C(12C,γ24Mg) heavy-ion radiative capture reaction. Similarities between both systems are investigated. [ABSTRACT FROM AUTHOR]

The 20Ne(p, γ)21Na reaction is the starting point of the NeNa cycle, which is an important process for the production of intermediate mass elements. The Ec.m. = 1113 keV resonance plays an important role in the determination of stellar rates for this reaction since it is used to normalize experimental direct capture yields at lower energies. The commonly accepted strength of this resonance, ωγ = 1.13 ± 0.07 eV, has been misinterpreted as the strength in the center-of-mass frame when it is actually the strength in the laboratory frame. This has motivated a new measurement of the Ec.m. = 1113 keV resonance strength in 20Ne(p, γ)21Na using the DRAGON recoil mass spectrometer. The DRAGON result, 0.972 ± 0.11 eV, is in good agreement with the accepted value when both are calculated in the same frame of reference. [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 masses of 40 neutron-rich nuclides from Z = 51 to 64 were measured at an average precision of δm/m = 10-7 using the Canadian Penning Trap mass spectrometer at Argonne National Laboratory. The measurements, of fission fragments from a 252Cf spontaneous fission source in a helium gas catcher, approach the predicted path of the astrophysical r process. Where overlap exists, this data set is largely consistent with previous measurements from Penning traps, storage rings, and reaction energetics, but large systematic deviations are apparent in β-endpoint measurements. Differences in mass excess from the 2003 Atomic Mass Evaluation of up to 400 keV are seen, as well as systematic disagreement with various mass models. [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]

In stellar helium burning, 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 capture reaction rate of 16O(α,γ)20Ne at Ec.m.=2.26 MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment. [ABSTRACT FROM AUTHOR]