Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars (exceeding eight solar masses) and superbursts from accreting neutron stars. It proceeds through the C +C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23-that is, C(C, α)Ne and C(C, p)Na-at temperatures greater than 0.4 × 10 kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars. The cross-sections for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have hitherto not been measured at the Gamow peaks below 2 megaelectronvolts because of exponential suppression arising from the Coulomb barrier. The reference rate at temperatures below 1.2 × 10 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the C(C, α)Ne and C(C, p)Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of Ne andNa, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method and the deuteron in N. The cross-sections deduced exhibit several resonances that are responsible for very large increases of the reaction rate at relevant temperatures. In particular, around 5 × 10 kelvin, the reaction rate is boosted to more than 25 times larger than the reference value . This finding may have implications such as lowering the temperatures and densities required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars to reconcile observations with theoretical models .

Three-body correlations for the ground-state decay of the lightest two-proton emitter 6 Be are studied both theoretically and experimentally. Theoretical studies are performed in a three-body hyperspherical-harmonics cluster model. In the experimental studies, the ground state of 6 Be was formed following the α decay of a 10 C beam inelastically excited through interactions with Be and C targets. Excellent agreement between theory and experiment is obtained demonstrating the existence of complicated correlation patterns which can elucidate the structure of 6 Be and, possibly, of the A=6 isobar.

We present the first study of the β decay of 23 Al undertaken with pure samples. The study was motivated by nuclear astrophysics questions. Pure samples of 23 Al were obtained from the momentum achromat recoil separator (MARS) of Texas A&M University, collected on a fast tape-transport system, and moved to a shielded location where β and β-γ coincidence measurements were made. We deduced β branching ratios and log ft values for transitions to states in 23 Mg, and from them determined unambiguously the spin and parity of the 23 Al ground state to be J π = 5/2 + . We discuss how this excludes the large increases in the radiative proton capture cross section for the reaction 22 Mg(p, γ ) 23 Al at astrophysical energies, which were implied by claims that the spin and parity is J π = 1/2 + . The log ft for the Fermi transition to its isobaric analog state (IAS) in 23 Mg is also determined for the first time. This IAS and a state 16 keV below it are observed, well separated in the same experiment for the first time. We can now solve a number of inconsistencies in the literature, exclude strong isospin mixing claimed before, and obtain a new determination of the resonance strength. Na(p, γ ) 23 Mg have both been suggested as possible candidates for diverting some of the flux in oxygen-neon novae explosions from the A = 22 into the A = 23 mass chain.

The differential cross sections for the reactions 9 Be(10 B, 10 B) 9 Be and 9 Be(10 B, 9 Be) 10 B have been measured at an incident energy of 100 MeV. The elastic scattering data have been used to determine the optical model parameters for the 9 Beϩ 10 B system at this energy. These parameters are then used in distorted-wave Born approximation ͑DWBA͒ calculations to predict the cross sections of the 9 Be(10 B, 9 Be) 10 B proton exchange reaction, populating the ground and low-lying states in 10 B. By normalizing the theoretical DWBA proton exchange cross sections to the experimental ones, the asymptotic normalization coefficients ͑ANC's͒, defining the normalization of the tail of the 10 B bound state wave functions in the two-particle channel 9 Beϩp, have been found. The ANC for the virtual decay 10 B(g.s.)→ 9 Beϩp will be used in an analysis of the 10 B(7 Be, 8 B) 9 Be reaction to extract the ANC's for 8 B→ 7 Beϩp. These ANC's determine the normalization of the 7 Be(p,␥) 8 B radiative capture cross section at very low energies, which is crucially important for nuclear astrophysics. ͓S0556-2813͑97͒02109-2͔

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