Properties of 20Na, 24Al, 28P, 32Cl, and 36K for studies of explosive hydrogen burning

The radiative proton-capture reactions Ne-19(p, gamma)Na-20, Mg-23(p, gamma) Al-24, Si-27(p, gamma)P-28, S-31(p, gamma)Cl-32, and Ar-35(p, gamma)K-36 potentially influence energy generation and/or nucleosynthesis during explosive hydrogen burning in classical novae and/or type I x-ray bursts. The thermonuclear rates of these reactions are dependent on resonance energies Er = Ex - Q and strengths omega gamma. The Ne-20(He-3,t)Na-20, Mg-24(He-3,t)Al-24, Si-28(He-3,t)P-28, S-32(He-3,t)Cl-32, and Ar-36(He-3,t)K-36 reactions have been measured using a 32-MeV, He-3(2+) beam; ion-implanted carbon-foil targets developed at the University of Washington; and the Munich Q3D magnetic spectrograph. This experiment has already yielded precision mass measurements of Na-20, Al-24, P-28, and Cl-32 [ C. Wrede et al., Phys. Rev. C 81, 055503 (2010)], which are used presently to constrain the corresponding (p, gamma) reaction Q values. The new Al-24 and P-28 masses resolve a discrepancy in the energy of the lowest-energy resonance in the 23Mg(p, gamma)Al-24 reaction and better constrain a direct measurement of its strength. Excitation energies in 32Cl and 36K have also been measured. An important new proton-unbound level has been found at E-x = 2196.9(7) keV in 36K and the uncertainties in 36K excitation energies have been reduced by over an order of magnitude. Using the new data on 36K, the A = 36, T = 1 triplets have been reassigned. The thermonuclear Ar-35(p, gamma)K-36 reaction rate is found to be much higher than a commonly adopted rate and this could affect energy generation in type I x-ray bursts.