N. P. T. Bateman

The dispersal of iron through the interstellar medium

Simple calculations on the dispersal of iron through the interstellar medium (ISM) indicate that cloud motions may be the most important mechanism for this dispersal, whereas turbulence in the intercloud gas and, in a three-phase ISM, supernova shocks probably play a lesser role. The calculations raise some doubts as to the importance of chimneys for mixing on a Galactic scale, though there is insufficient observational data to draw more than tentative conclusions. The distance over which iron produced by a supernova in the local Galactic disk is mixed over one recycling time of the ISM is found to be between about 0.5 and 2.0 kpc, consistent with the chemical homogeneity of star clusters and the observed gradient in [Fe/H]

On the Production of 26Al 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)26Algs reaction. We have measured the yield of 26Al 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 of 26Al, it appears that 26Al was produced in a stellar environment, and not by cosmic rays.

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}