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Angular distributions of 12C(alpha,alpha)12C have been measured for E(alpha) = 2.6-8.2 MeV, at angles from 24 to 166, yielding 12 864 data points. R-matrix analysis of the ratios of elastic scattering yields a reduced width amplitude of gamma12 = 0.47 +/- 0.06 MeV(1/2) for the Ex = 6.917 MeV (2+) state in 16O(a = 5.5 fm). The dependence of the chi2 surface on the interaction radius a has been investigated and a deep minimum is found at a = 5.42(+0.16)(-0.27) fm. Using this value of gamma12, radiative alpha capture and 16N beta-delayed alpha-decay data, the S factor is calculated at E(c.m.) = 300 keV to be S(E2)(300) = 53(+13)(-18) keV b for destructive interference between the subthreshold resonance tail and the ground state E2 direct capture.

The 28 Si͑a, 8 He͒ 24 Si reaction has been used to measure the energies of the first two excited states in 24 Si. The excitation energies were found to be 1.879 6 0.011 and 3.441 6 0.010 MeV. These data allow for the first time the calculation of the stellar reaction rate of 23 Al͑ p, g͒ 24 Si on the basis of experimental information. This reaction is of considerable interest, since it might lead to a decrease of the 22 Na production in nova explosions, and solve the discrepancy between the 22 Na yield predictions of nova models and recent COMPTEL observations. We show, however, that the temperatures and densities required for a significantly reduced 22 Na yield are not reached in current nova models. [S0031-9007(97)04602-4]

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