Extracting the asymptotic normalization coefficients in neutron transfer reactions to determine the reaction rates for magnesium-22(proton,gamma)-aluminum-23 and fluorine-17(proton,gamma)-neon-18

The nucleosynthesis of the beta+-unstable 18 F and 22Na nuclei in oxygen-neon novae is considered one of the crucial subjects in the field of nuclear astrophysics. They are produced in thermonuclear runaway processes via radiative proton-capture reactions and may be ejected into the stellar medium when the sudden outbursts of the envelope occur. Recent observations with gamma-ray telescopes, however, have not detected those long-lived gamma-ray emitters.;The problem is to study the importance of the rates of the 17 F(p,gamma)18Ne and 22Mg( p,gamma)23Al reactions that may influence the abundances of 18F and 22Na, respectively. To investigate their productions, an indirect technique has been applied to determine these reaction rates at stellar energies through measurements of the asymptotic normalization coefficients (ANCs) in the mirror nuclear systems. The ANCs for 18O and 23Ne are obtained from the neutron transfer reactions 13C(17O, 18O) 12C and 13C(22Ne, 23Ne) 12C at 12 MeV/nucleon, respectively. The ANC of 13C, which represents the other vertex in the transfer reactions, has also been measured to be C2p1/2 = 2.31 +/- 0.08 fm-1.;The differential cross-sections for the reaction 13C( 22Ne, 23Ne)12C because of transitions from the Jpi = 12 - in 13C to the Jpi = 52 + and 12 + states in 23Ne, have been detected. Optical model parameters for use in the DWBA calculations were obtained from measurements of the elastic scatterings 22Ne+13C and 22Ne+ 12C at the same energy. The extracted ANCs in 23Ne are transposed to their corresponding values in 23Al. The astrophysical S-factor S1-22(0) was determined to be 961 +/- 105 eVb. The reaction rate calculated from these results shows that the 22Mg(p,gamma)23Al reaction may reduce the production of 22Na in massive novae M ≈ 1.35 M⊙ .;A similar procedure has been followed in studying the 13C( 17O, 18O)12C reaction. The ANCs related to the Jpi = ( 0+1,2+1,4+ 1,2+2 ) states in 18Ne were determined from their corresponding values in 18O, then used to calculate S 1-17(0) = 2.5 +/- 0.4 keV b. These results show that the reaction rate of 17F(p,gamma )18Ne is dominated by the direct capture to the 2+2 and 2+1 states at astrophysical energies. The calculated reaction rate is considered to be slow, which leads to an increase in the production of 18F in oxygen-neon novae.