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We have studied the properties of low-lying ${}^{18}\mathrm{F}+p$ resonances as excited states in ${}^{19}\mathrm{Ne}.$ Three new levels have been found in the range $0l~{E}_{\mathrm{c}.\mathrm{m}.}l~1 \mathrm{MeV}$ just above the ${}^{18}\mathrm{F}+p$ threshold, and partial decay widths and isospin-mirror connections are suggested to known states in ${}^{19}\mathrm{F}$ for each of the nine states in this energy range. The properties of these resonances have been used to calculate the reaction rate ${N}_{A}〈\ensuremath{\sigma}v〉$ for the ${}^{18}\mathrm{F}(p,\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ and ${}^{18}\mathrm{F}(p,\ensuremath{\alpha}{)}^{15}\mathrm{O}$ reactions in the temperature range ${10}^{8}lTl{10}^{9}.$ A comparison of these rates indicates that in this temperature range, the ${}^{14}\mathrm{O}(\ensuremath{\alpha}{,p)}^{17}\mathrm{F}(p,\ensuremath{\gamma}{)}^{18}\mathrm{Ne}{(e}^{+}\ensuremath{\nu}{)}^{18}\mathrm{F}(p,\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ reaction sequence is not as fast as the ${}^{15}\mathrm{O}(\ensuremath{\alpha},\ensuremath{\gamma}{)}^{19}\mathrm{Ne}$ reaction.

Clayton and Jin have proposed that {sup 26}Al in the early solar system was made by oxygen-rich cosmic rays through the {sup 12}C({sup 16}O,x){sup 26}Al{sub g.s.} reaction. To test their proposal we have measured the yield of {sup 26}Al{sub g.s.} from this reaction using the activation method. We find that the yield is too low to explain the {sup 26}Al/{sup 27}Al ratio that has been observed in carbonaceous chondrite meteorites. {copyright} {ital 1998} {ital The American Physical Society}

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.

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.

We used the $^{16}\mathrm{O}$${(}^{3}$He,n${)}^{18}$Ne, $^{12}\mathrm{C}$${(}^{12}$C${,}^{6}$He${)}^{18}$Ne, and $^{20}\mathrm{Ne}$(p,t${)}^{18}$Ne reactions to study $^{18}\mathrm{Ne}$ states up to an excitation energy of 10 MeV, with emphasis on levels corresponding to $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F and $^{17}\mathrm{F}$(p,\ensuremath{\gamma}${)}^{18}$Ne resonances that could strongly affect these reaction rates in hot stellar environments. Excitation energies, widths, absolute cross sections, and angular distributions were measured. We found previously unidentified states at ${\mathit{E}}_{\mathit{x}}$=6.15\ifmmode\pm\else\textpm\fi{}0.01 MeV, 7.12\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.35\ifmmode\pm\else\textpm\fi{}0.02 MeV, 7.62\ifmmode\pm\else\textpm\fi{}0.02 MeV, 8.30\ifmmode\pm\else\textpm\fi{}0.02 MeV, (8.45\ifmmode\pm\else\textpm\fi{}0.03 MeV), 8.55\ifmmode\pm\else\textpm\fi{}0.03 MeV, 8.94\ifmmode\pm\else\textpm\fi{}0.02 MeV, and 9.58\ifmmode\pm\else\textpm\fi{}0.02 MeV. We combined level width, cross section, and angular distribution data to infer ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$ values for a number of the new levels as well as for the previously known 5.1-MeV doublet. Using information from our experiments, we recalculated the $^{14}\mathrm{O}$(\ensuremath{\alpha},p${)}^{17}$F reaction rate, which constitutes a possible path out of the hot CNO cycle into the rp process and could play an important role in transforming nuclei involved in the hot CNO cycle into heavier nuclei with Z\ensuremath{\ge}10. \textcopyright{} 1996 The American Physical Society.

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,\ensuremath{\alpha}) reactions along the process path which lead to the formation of reaction cycles rather than to chains of proton capture processes and \ensuremath{\beta} decays. Previous direct attempts to measure the low-energy reaction cross sections for $^{31}\mathrm{P}$(p,\ensuremath{\alpha}${)}^{28}$Si and $^{35}\mathrm{Cl}$(p,\ensuremath{\alpha}${)}^{32}$S 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 $^{36}\mathrm{Ar}$. The results allow a more accurate determination of the contributions of these low-energy levels in the (p,\ensuremath{\alpha}) reaction channel.

Wiescher, G\"orres, and Thielemann suggested that a "missing" ${J}^{\ensuremath{\pi}}={3}^{+}$ level in $^{18}\mathrm{Ne}$ should occur at ${E}_{x}\ensuremath{\approx}4.33$ MeV, only \ensuremath{\approx}410 keV above the $^{17}\mathrm{F}$+$p$ threshold. They noted that this level would provide an $s$-wave resonance in the $^{17}\mathrm{F}(p, \ensuremath{\gamma})$ reaction, greatly increasing its thermonuclear reaction rate. This, in turn, would have a pronounced effect on the production of $^{17}\mathrm{O}$ and $^{18}\mathrm{O}$ in explosive stellar environments. We have searched for this level using the $^{16}\mathrm{O}(^{3}\mathrm{He}, n)$ reaction. High-resolution time-of-flight spectra show that the ${3}^{+}$ level occurs at ${E}_{x}=4.561\ifmmode\pm\else\textpm\fi{}0.009$ MeV, \ensuremath{\approx}230 keV higher than suggested. The astrophysical consequences of this result are discussed.

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.

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

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.

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]