On the production of26A1 in the early solar system by low-energy oxygen cosmic rays

Clayton & Jin have proposed that the high abundance of 26Al found in meteorites was produced by cosmic rays in the early solar system through the 12C(16O,x)26Ales reaction. We have measured the yield of 26A1 in the ground state (i.e., 26Algs) from this reaction and find that, if this mechanism produced the meteoritic 26Al, a substantial fraction of the solar system oxygen must have entered the solar system as low-energy cosmic rays. This does not seem plausible. If the proto-Sun itself was the source of the oxygen cosmic rays, they must have carried off some 5% of the power of the protosolar wind for 1 Myr. This too seems unlikely. Although we do not address the role of other cosmic-ray species in the production of26 Al, it appears that 26A1 was produced in a stellar environment, and not by cosmic rays

Indirect study of low-energy resonances in P31(p,)28Si and Cl35(p,)32S

The reaction sequences governing the reaction flow in the rp process are important for the understanding of the energy generation and nucleosynthesis of heavy elements in hot and explosive stellar hydrogen burning. Of considerable interest are (p,) reactions along the process path which lead to the formation of reaction cycles rather than to chains of proton capture processes and decays. Previous direct attempts to measure the low-energy reaction cross sections for P31(p,)28Si and Cl35(p,)32S resulted only in upper limits for the strengths of possible low-energy resonances which may dominate the reaction rates. In this paper an indirect experimental approach is presented to study the structure of the low-energy unbound states in the compound nuclei 32 S and Ar36. The results allow a more accurate determination of the contributions of these low-energy levels in the (p,) reaction channel

Breakout from the hot CNO cycle: The 18F(p,γ) vs 18F(p,α) branching ratio

We have studied the properties of low-lying 18Fp resonances as excited states in 19Ne. Three new levels have been found in the range 0Ec.m.1 MeV just above the 18Fp threshold, and partial decay widths and isospin-mirror connections are suggested to known states in 19F for each of the nine states in this energy range. The properties of these resonances have been used to calculate the reaction rate NAvfor the 18F(p,)19Ne and 18F(p,)15O reactions in the temperature range 108T109. A comparison of these rates indicates that in this temperature range, the 14O(,p)17F(p,)18Ne(e)18F(p,)19Ne reaction sequence is not as fast as the 15O(,)19Ne reaction

β-delayed particle decay of 17ne into p + α + 12C through the isobaric analog state in 17F

We have observed the breakup of the isobaric analog state at 11.193 MeV in 17F into three particles via three channels: proton decay to the α-unbound 9.585 MeV state in 16O; and α decay to the proton-unbound 2.365 and 3.502/3.547 MeV states in 13N. Laboratory α-particle spectra corresponding to these three modes have been generated in Monte Carlo simulations using single-channel, single- and multilevel R-matrix formulas. A fit of these spectra to the α spectrum resulting from a triple-coincidence measurement results in excellent agreement with the experimental spectrum and allows branching ratios to be deduced for these rare decay modes