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Data have been obtained on exclusive single neutron knockout cross sections from 12Be to study its ground state structure. Preliminary cross sections for the first (0.32 MeV, $\ensuremath{^1\!/_2 ^-}$) and second (1.78 MeV, $\ensuremath{^5\!/_2 ^+}$, unbound) excited states in 11Be have been obtained, giving evidence of significant admixtures of both $\ensuremath{\nu(1p_{^1\!/_2})^2}$ and $\ensuremath{\nu(1d_{^5\!/_2})^2}$ configurations in the ground state of 12Be. [ABSTRACT FROM AUTHOR]

The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the γ-ray observable radioisotope 18F, produced in novae. However, no successful measurement of this reaction exists and the rate used is calculated from incomplete information on the contributing resonances. Of the two resonances thought to play a significant role, one has a radiative width estimated from the assumed analogue state in the mirror nucleus, 19F. The second does not have an analogue state assignment at all, resulting in an arbitrary radiative width being assumed. Here, we report the first successful direct measurement of the 18F(p,γ)19Ne reaction. The strength of the 665 keV resonance (Ex=7.076 MeV) is found to be over an order of magnitude weaker than currently assumed in nova models. Reaction rate calculations show that this resonance therefore plays no significant role in the destruction of 18F at any astrophysical energy. [ABSTRACT FROM AUTHOR]

Background: The rate of the 18F(p,γ)19Ne reaction affects the final abundance of the radioisotope 18F ejected from novae. This nucleus is important as its abundance is thought to significantly influence the first-stage 511-keV and continuum γ-ray emission in the aftermath of novae. No successful measurement of this reaction existed prior to this work, and the rate used in stellar models had been calculated based on incomplete information from contributing resonances. Purpose: Of the two resonances thought to provide a significant contribution to the astrophysical reaction rate, located at Ec.m.=330 and 665 keV, the former has a radiative width estimated from the assumed analog state in the mirror nucleus, 19F, while the latter resonance does not have an analog state assignment, resulting in an arbitrary radiative width being assumed. As such, a direct measurement was needed to establish what role this resonance plays in the destruction of 18F at nova temperatures. This paper extends and takes the place of a previous Letter which reported the strength of the Ec.m.=665 keV resonance. Method: The DRAGON recoil separator was used to directly measure the strength of the important 665-keV resonance in this reaction, in inverse kinematics, by observing 19Ne reaction products. A radioactive 18F beam was provided by the ISAC facility at TRIUMF. R-matrix calculations were subsequently used to evaluate the significance of the results at astrophysical energies. Results: We report the direct measurement of the 18F(p,γ)19Ne reaction with the reevaluation of several detector efficiencies and the use of an updated 19Ne level scheme in the reaction rate analysis. The strength of the 665-keV resonance (Ex=7.076 MeV) is found to be an order of magnitude weaker than currently assumed in nova models. An improved analysis of the previously reported data is presented here, resulting in a slightly different value for the resonance strength. These small changes, however, do not alter the primary conclusions. Conclusions: Reaction rate calculations definitively show that the 665-keV resonance plays no significant role in the destruction of 18F at nova temperatures. [ABSTRACT FROM AUTHOR]

Uncertainties in the thermonuclear rates of the 15O(α, γ)l9Ne and l8F(p, α)15O reactions affect model predictions of light curves from type I x-ray bursts and the amount of the observable radioisotope 18F produced in classical novae, respectively. To address these uncertainties, we have studied the nuclear structure of 19Ne over Ex=4.0-5.1 and 6.1-7.3 MeV using the l9F(³He, t) l9Ne reaction. We find the Jπ values of the 4.14-and 4.20-MeV levels to be consistent with 9/2- and 7/2-, respectively, in contrast to previous assumptions. We confirm the recently observed triplet of states around 6.4 MeV and find evidence that the state at 6.29 MeV, just below the proton threshold, is either broad or a doublet. Our data also suggest that predicted but yet unobserved levels may exist near the 6.86-MeV state. Higher resolution experiments are urgently needed to further clarify the structure of 19Ne around the proton threshold before a reliable 18F(p,α)15O rate for nova models can be determined. [ABSTRACT FROM AUTHOR]

26Al is an important radioisotope in astrophysics that provides evidence of ongoing nucleosynthesis in the Galaxy. The 23Na(α, p)26Mg reaction has been identified by a sensitivity study as being one of the most important reactions for the production of 26Al in the convective C/Ne burning shell of massive stars. Owing to large uncertainties in previous experimental data, model calculations are used for the reaction rate of 23Na(α, p)26Mg in this sensitivity study. Current experimental data suggest a reaction rate a factor of ~40 higher than model calculations. However, a new measurement of this reaction cross section has been made in inverse kinematics in the energy range Ec.m. = 1.28–3.15 MeV at TRIUMF, and found to be in reasonable agreement with the model calculation. A new reaction rate is calculated and tight constraints on the uncertainty in the production of 26Al, due to this reaction, are determined. [ABSTRACT FROM AUTHOR]

The reaction mechanisms of the two-neutron transfer reaction 12C(6He,4He) have been studied at Elab = 30 MeV at the TRIUMF ISAC-II facility using the Silicon Highly-segmented Array for Reactions and Coulex (SHARC) charged-particle detector array. Optical potential parameters have been extracted from the analysis of the elastic scattering angular distribution. The new potential has been applied to the study of the transfer angular distribution to the 22+ 8.32 MeV state in 14C, using a realistic three-body 6He model and advanced shell-model calculations for the carbon structure, allowing to calculate the relative contributions of the simultaneous and sequential two-neutron transfer. The reaction model provides a good description of the 30-MeV data set and shows that the simultaneous process is the dominant transfer mechanism. Sensitivity tests of optical potential parameters show that the final results can be considerably affected by the choice of optical potentials. A reanalysis of data measured previously at Elab = 18 MeV, however, is not as well described by the same reaction model, suggesting that one needs to include higher-order effects in the reaction mechanism. [ABSTRACT FROM AUTHOR]

The article presents a comparison of mirror symmetry in the A = 23, T = 1/2 mirror nuclei 23Na and 23Mg both to high spin, and high excitation energy, including beyond the proton threshold. Excited states in the region above the proton threshold have been studied in both nuclei. It presents methods of obtaining reaction rates for nuclear astrophysics. It concludes that estimated data of shell model calculations can be used if real data is not available.

The inclusive breakup for the 11Li+208Pb reaction at energies around the Coulomb barrier has been measured for the first time. A sizable yield of 9Li following the 11Li dissociation has been observed, even at energies well below the Coulomb barrier. Using the first-order semiclassical perturbation theory of Coulomb excitation it is shown that the breakup probability data measured at small angles can be used to extract effective breakup energy as well as the slope of B(E1) distribution close to the threshold. Four-body continuum-discretized coupled-channels calculations, including both nuclear and Coulomb couplings between the target and projectile to all orders, reproduce the measured inclusive breakup cross sections and support the presence of a dipole resonance in the 11Li continuum at low excitation energy. [ABSTRACT FROM AUTHOR]