We have made new, improved measurements of the Si28-30 (n, gamma) cross sections and have done a resonance analysis of these data including previous total cross sections. Together with the calculated contributions due to direct capture, we calculated the astrophysical (n, gamma) reaction rates and investigated the s-process abundances of the Si isotopes. Measured isotopic anomalies of intermediate and heavy elements in SiC grains from meteorites appear to be attributable to the s-process in asymptotic giant branch (AGB) stars. But the Si isotopic ratios in these grains are substantially different than s-process models predict. Therefore, recent papers have invoked galactic chemical evolution or other effects to explain the Si isotope ratios in these grains. Our new reaction rates are significantly different than previous rates, and s-process calculations using these rates lead to much larger isotopic shifts in Si-30. However, these exploratory calculations demonstrate that even with these substantially different rates the large observed variation in SiC grain from AGB stars cannot be explained by standard s-process models

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We have measured the 147 Sm(n,α) cross section from 3 eV to 500 keV and performed an Rmatrix analysis in the resolved region (En< 700 eV) to extract α widths for 104 resonances. We computed strength functions from these resonance parameters and compared them to transmission coefficients calculated using optical model potentials similar to those employed as inputs to statistical model calculations. The statistical model often is used to predict cross sections and astrophysical reaction rates. Comparing resonance parameters rather than cross sections allows more direct tests of potentials used in the model and hence should offer greater insight into possible improvements. In particular, an improved α+nucleus potential is needed for applications in nuclear astrophysics. In addition to providing a more direct test of the α+nucleus potential, the α-width distributions show indications of non-statistical effects.PACS numbers:

We have measured the 26 Al(n,␣ 0 ) 23 Mg and 26 Al(n, p 1 ) 26 Mg* cross sections from thermal energy to approximately 10 keV and 70 keV, respectively. These reactions are thought to be the major mechanisms for the destruction of 26 Al in many nucleosynthesis environments; hence, an accurate determination of their rates is important for understanding the observations of ␥ rays from ''live'' 26 Al in our galaxy and of ''extinct'' 26 Al in meteorites. The astrophysical rate for the 26 Al(n,␣ 0 ) 23 Mg reaction determined from our measurements is in good agreement with the rate determined via inverse measurements. On the other hand, the rate we determined for the 26 Al(n,p 1 ) 26 Mg* reaction is significantly larger than previously reported. In addition, we were able to determine this rate in the temperature range below 0.2 GK which was not covered by previous measurements. This lower temperature range may be important for understanding the production of 26 Al in Red Giant stars. Both of our rates are significantly different than the rates used in most nucleosynthesis calculations. We discuss the impact of our measurements on the nucleosynthesis of 26 Al.

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