Measurement and DWBA analysis of the 12C(6Li,d)16O α-transfer reaction cross sections at 48.2 MeV.: R-matrix analysis of 12C(α,γ)16O direct capture reaction data

The angular distributions for low lying states of O-16 produced in the C-12(Li-6,d)O-16 alpha-transfer reaction at E-6Li(lab) = 48.2 MeV have been measured using a high energy resolution position sensitive detection system. The measured cross section data have been analyzed by the FRDWBA theory with a particular emphasis put on the states of astrophysical interest mainly the 1(-) (7.12 MeV) state. Extracted values of nuclear level parameters (excitation energy, E-x, line width, Gamma(c.m.), alpha-spectroscopic factor, S-alpha, and reduced a-width, gamma(2)(alpha) or theta(2)(alpha)) are reported and discussed in comparison to previous ones. The used binding potential corresponds to a long nuclear interaction range (up to a channel radius a = 7.7 fm), suggesting that the channel radius a = 6.5 fm is likely suitable for the calculations of reduced alpha-widths near the nuclear surface. However, given that previous DWBA results are available for comparison only near the channel radius a = 5.5 fm, calculations have been carried out here for both three preceding a values. Formal values, 0.0036 0.0036 <= theta(2)(alpha)(7.12) <= 0.152 and 0.019 <= theta(2)(alpha)(6.92) <= 0.096 of the reduced alpha-widths (a = 6.5 fm) of the 1(-) (7.12 MeV) and 2(+) (6.92 MeV) states have thus been derived. Furthermore, the R-matrix analysis of various data sets of importance to the C-12(alpha,gamma)O-16 direct capture reaction has been carried out, leading to the range of values for the 1(-) (7.12 MeV) state, 0.0096 <= theta(2)(alpha)(7.12) <= 0.0166, which is consistent with the preceding DWBA interval, and to a result for the El component of the reaction astrophysical factor, S-E vertical bar(0.3) = 80.6(-16)(+17) keVb, very constrained values previously reported in the literature. (C) 2007 Elsevier B.V. All rights reserved.