K. Yildiz

The production of 26al in the early solar system by oxygen rich cosmic rays

Abstract Clayton and Jin[1] have proposed that the meteoritic 26 Al was produced by low energy cosmic rays in the early solar system through the 12 C( 16 O,x) 26 Al reaction. We have measured the yield of 26 Al from this reaction and find that it is too low to explain the meteorite observations.

Investigating the astrophysically important Ex = 2.646 MeV state in 20Na

Abstract Observations of neon lines in the spectra of energetic novae have prompted a renewed look at explosive hydrogen burning. The 19Ne(p, γ)20Na reaction is expected to play a major role in the breakout of the hot CNO cycle to the rp-process, which can process CNO nuclei to heavier elements. The reaction rate is dominated by the lowest resonance in the 19Ne + p system, corresponding to the Ex = 2.646 MeV state in 20Na. A large variety of nuclear experimental techniques have been used to study this state; e.g. charge exchange reactions, β-delayed proton decay and radioactive beams. Their results have lead to a Jπ = 3+ assignment for this state [B. Brown et al., Phys. Rev. C 48 (1993) 1456], allowing an estimate of the proton width (Γp). This leaves the gamma width (Γγ) to be determined. We have performed 20Ne(3He, experiments to measure the branching ratio ( Γ γ Γ ) of the Ex = 2.646 MeV excited state in 20Na.

Measurement of the Γγ/Γtot of the Ex=2.646 MeV state in 20Na

In energetic nova events, breakout of the hot CNO cycle may proceed via the reaction chain 15O(α,γ)19Ne(p,γ)20Na. This triggers a sequence of rapid proton captures and beta decays which can process CNO nuclei to heavier elements (rp‐process). The rate of the 19Ne(p,γ)20Na reaction is sensitive to resonances in the 19Ne+p system. The first excited state above the proton threshold of 2.199 MeV in 20Na (at Ex=2.646 MeV) is expected to be the most important in determining the reaction rate. The gamma width (Γγ) of this state is still unknown and the Jπ assignment of this state is currently the subject of debate (1). We have performed 20Ne(3He,tγ) experiments to determine the branching ratio Γγ/Γ of the Ex=2.646 MeV excited state in 20Na. Some preliminary results of these experiments will be presented.

Thick target yields of {sup 26}Al{sub g.s.} from the {sup 16}O({sup 16}O,x){sup 26}Al{sub g.s.} and {sup 16}O({sup 14}N,x){sup 26}Al{sub g.s.} reactions

Extending the earlier work of Bateman {ital et al}., we have measured the energy-integrated yield of {sup 26}Al{sub g.s.} from the {sup 16}O({sup 16}O,x){sup 26}Al{sub g.s.} and {sup 16}O({sup 14}N,x){sup 26}Al{sub g.s.} reactions. We find that although the yield from the {sup 16}O({sup 16}O,x){sup 26}Al{sub g.s.} reaction is several times larger than from the {sup 12}C({sup 16}O,x){sup 26}Al{sub g.s.} reaction, the abundance of fossil {sup 26}Al{sub g.s.} observed in carbonaceous chondrite meteorites could be produced by oxygen-rich cosmic rays via the {sup 16}O({sup 16}O,x){sup 26}Al{sub g.s.} reaction only under the improbable scenario that more than 40{percent} of the solar system oxygen was injected into the protosolar nebula as cosmic rays. thinsp {copyright} {ital 1999} {ital The American Physical Society}