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The thermonuclear ^{30}P(p,γ)^{31}S reaction rate is critical for modeling the final elemental and isotopic abundances of ONe nova nucleosynthesis, which affect the calibration of proposed nova thermometers and the identification of presolar nova grains, respectively. Unfortunately, the rate of this reaction is essentially unconstrained experimentally, because the strengths of key ^{31}S proton capture resonance states are not known, largely due to uncertainties in their spins and parities. Using the β decay of ^{31}Cl, we have observed the β-delayed γ decay of a ^{31}S state at E_{x}=6390.2(7) keV, with a ^{30}P(p,γ)^{31}S resonance energy of E_{r}=259.3(8) keV, in the middle of the ^{30}P(p,γ)^{31}S Gamow window for peak nova temperatures. This state exhibits isospin mixing with the nearby isobaric analog state at E_{x}=6279.0(6) keV, giving it an unambiguous spin and parity of 3/2^{+} and making it an important l=0 resonance for proton capture on ^{30}P.

Classical novae are expected to contribute to the 1809-keV Galactic $\ensuremath{\gamma}$-ray emission by producing its precursor $^{26}\mathrm{Al}$, but the yield depends on the thermonuclear rate of the unmeasured $^{25}\mathrm{Al}(p,\ensuremath{\gamma})^{26}\mathrm{Si}$ reaction. Using the $\ensuremath{\beta}$ decay of $^{26}\mathrm{P}$ to populate the key ${J}^{\ensuremath{\pi}}={3}^{+}$ resonance in this reaction, we report the first evidence for the observation of its exit channel via a $1741.6\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{syst})\text{ }\text{ }\mathrm{keV}$ primary $\ensuremath{\gamma}$ ray, where the uncertainties are statistical and systematic, respectively. By combining the measured $\ensuremath{\gamma}$-ray energy and intensity with other experimental data on $^{26}\mathrm{Si}$, we find the center-of-mass energy and strength of the resonance to be ${E}_{r}=414.9\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.3(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}0.6(\mathrm{lit}.)\text{ }\text{ }\mathrm{keV}$ and $\ensuremath{\omega}\ensuremath{\gamma}=23\ifmmode\pm\else\textpm\fi{}6(\mathrm{stat}{)}_{\ensuremath{-}10}^{+11}(\mathrm{lit}.)\text{ }\text{ }\mathrm{meV}$, respectively, where the last uncertainties are from adopted literature data. We use hydrodynamic nova simulations to model $^{26}\mathrm{Al}$ production showing that these measurements effectively eliminate the dominant experimental nuclear-physics uncertainty and we estimate that novae may contribute up to 30% of the Galactic $^{26}\mathrm{Al}$.

Studies of 6He beta decay along with tritium can play an important role in testing ab initio nuclear wave-function calculations and may allow for fixing low-energy constants in effective-field theories. Here, we present an improved determination of the 6He half-life to a relative precision of 3×10(-4). Our value of 806.89±0.11(stat)(-0.19syst)(+0.23) ms resolves a major discrepancy between previous measurements. Calculating the statistical rate function we determined the ft value to be 803.04(-0.23)(+0.26) s. The extracted Gamow-Teller matrix element agrees within a few percent with ab initio calculations.

The radionuclide 22 Na is a potential astronomical observable that is expected to be produced in classical novae in quantities that depend on the thermonuclear rate of the 22 Na(p, γ) 23 Mg reaction. We have measured the strengths of low-energy 22 Na(p, γ) 23 Mg resonances directly and absolutely using a radioactive 22 Na target. We find the strengths of resonances at E p = 213, 288, 454, and 610 keV to be higher than previous measurements by factors of 2.4—3.2, and we exclude important contributions to the rate from proposed resonances at E p = 198, 209, and 232 keV. The 22 Na abundances expected in the ejecta of classical novae are reduced by a factor of ≈ 2.

The possibility of observing neutrinoless double {beta} decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of {sup 76}Ge (a candidate for such decay) and {sup 76}Se (the daughter nucleus) were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations, the changes are confined primarily to one orbit.

Radiative {alpha}-particle capture into the first excited, J{sup {pi}}=0{sup +} state of {sup 16}O at 6.049 MeV excitation energy has rarely been discussed as contributing to the {sup 12}C({alpha},{gamma}){sup 16}O reaction cross section due to experimental difficulties in observing this transition. We report here measurements of this radiative capture in {sup 12}C({alpha},{gamma}){sup 16}O 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{sub 6.0}(300)=25{sub -15}{sup +16} keV b] showing that this transition is likely the most important cascade contribution for {sup 12}C({alpha},{gamma}){sup 16}O.

The strength of the Ec.m.=184 keV resonance in the 26gAl(p,gamma)27Si reaction has been measured in inverse kinematics using the DRAGON recoil separator at TRIUMF's ISAC facility. We measure a value of omegagamma=35±7 µeV and a resonance energy of Ec.m.=184±1 keV, consistent with p-wave proton capture into the 7652(3) keV state in 27Si, and discuss the implications of these values for 26gAl nucleosynthesis in typical oxygen-neon white-dwarf novae.

The 21Na(p,gamma)22Mg reaction is expected to play an important role in the nucleosynthesis of 22Na in oxygen-neon novae. The decay of 22Na leads to the emission of a characteristic 1.275 MeV gamma-ray line. This report provides the first direct measurement of the rate of this reaction using a radioactive 21Na beam, and discusses its astrophysical implications. The energy of the important state was measured to be E(c.m.)=205.7+/-0.5 keV with a resonance strength omegagamma=1.03+/-0.16(stat)+/-0.14(sys) meV.