Properties of Na20, Al24, P28, Cl32, and K36 for studies of explosive hydrogen burning
Keywords
Explosive burning in accreting binary systems, 20lt=Alt=38, Properties of nuclei_s19 nuclear energy levels, Charge-exchange reactions
Abstract
The radiative proton-capture reactions 19Ne(p,g)20Na, 23Mg(p,g)24Al, 27Si(p,g)28P, 31S(p,g)32Cl, and 35Ar(p,g)36K 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 _s13_s17969_s19_s13_s17947_s19. The 20Ne(3He,t)20Na, 24Mg(3He,t)24Al, 28Si(3He,t)28P, 32S(3He,t)32Cl, and 36Ar(3He,t)36K reactions have been measured using a 32-MeV, 3He2_s16 beam_s19 ion-implanted carbon-foil targets developed at the University of Washington_s19 and the Munich Q3D magnetic spectrograph. This experiment has already yielded precision mass measurements of 20Na, 24Al, 28P, and 32Cl [C. Wrede et al., Phys. Rev. C 81, 055503 (2010)], which are used presently to constrain the corresponding (p,g) reaction Q values. The new 24Al and 28P masses resolve a discrepancy in the energy of the lowest-energy resonance in the 23Mg(p,g)24Al 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 Ex=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 35Ar(p,g)36K 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.
