L. Trache

Tests of transfer reaction determinations of astrophysical S factors

The {sup 16}O({sup 3}He,d){sup 17}F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of {sup 17}F. The coefficients provide the normalization for the tails of the overlap functions for {sup 17}F{r_arrow}{sup 16}O+p and allow us to calculate the {ital S} factors for {sup 16}O(p,{gamma}){sup 17}F at astrophysical energies. The calculated {ital S} factors are compared to measurements and found to be in very good agreement. This provides a test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in {sup 17}F, without the uncertainty associated with extrapolation from higher energies. {copyright} {ital 1999} {ital The American Physical Society}

A Novel Approach to Measure the Cross Section of the 18O(p, α)15N Resonant Reaction in the 0-200 keV Energy Range

The 18O(p, ?)15N reaction is of primary importance to pin down the uncertainties, due to nuclear physics input, affecting present-day models of asymptotic giant branch stars. Its reaction rate can modify both fluorine nucleosynthesis inside such stars and oxygen and nitrogen isotopic ratios, which allow one to constrain the proposed astrophysical scenarios. Thus, an indirect measurement of the low-energy region of the 18O(p, ?)15N reaction has been performed to access, for the first time, the range of relevance for astrophysical application. In particular, a full, high-accuracy spectroscopic study of the 20 and 90 keV resonances has been performed and the strengths deduced to evaluate the reaction rate and the consequences for astrophysics.

Tests of transfer reaction determinations of astrophysical {bold {ital S}} factors

The {sup 16}O({sup 3}He,d){sup 17}F reaction has been used to determine asymptotic normalization coefficients for transitions to the ground and first excited states of {sup 17}F. The coefficients provide the normalization for the tails of the overlap functions for {sup 17}F{r_arrow}{sup 16}O+p and allow us to calculate the {ital S} factors for {sup 16}O(p,{gamma}){sup 17}F at astrophysical energies. The calculated {ital S} factors are compared to measurements and found to be in very good agreement. This provides a test of this indirect method to determine astrophysical direct capture rates using transfer reactions. In addition, our results yield S(0) for capture to the ground and first excited states in {sup 17}F, without the uncertainty associated with extrapolation from higher energies. {copyright} {ital 1999} {ital The American Physical Society}

Asymptotic normalization coefficient of 8B from breakup reactions and the S17 astrophysical factor.

We show that asymptotic normalization coefficients (ANC) can be extracted from one-nucleon breakup reactions of loosely bound nuclei at 30-300 MeV/nucleon. In particular, the breakup of 8B is described in terms of an extended Glauber model. The 8B ANC extracted from breakup data at several energies and on different targets, C(2)(tot) = 0.450+/-0.039 fm(-1), leads to the astrophysical factor S17(0) = 17.4+/-1.5 eV b for the key reaction for solar neutrino production 7Be(p, gamma)8B. The procedure described provides an indirect method to determine reaction rates of astrophysical interest with beams of loosely bound radioactive nuclei.

Asymptotic normalization coefficients for B-8 ---> Be-7 + p from a study of Li-8 ---> Li-7 + n

Asymptotic normalization coefficients (ANCs) for 8Li->7Li+n have been extracted from the neutron transfer reaction 13C(7Li,8Li)12C at 63 MeV. These are related to the ANCs in 8B->7Be+p using charge symmetry. We extract ANCs for 8B that are in very good agreement with those inferred from proton transfer and breakup experiments. We have also separated the contributions from the p_1/2 and p_3/2 components in the transfer. We find the astrophysical factor for the 7Be(p,gamma)8B reaction to be S_17(0)=17.6+/-1.7 eVb. This is the first time that the rate of a direct capture reaction of astrophysical interest has been determined through a measurement of the ANCs in the mirror system.

High precision measurement of the superallowed 0+ --> 0+ beta decay of 22Mg.

The half-life, 3.8755(12) s, and superallowed branching ratio, 0.5315(12), for 22Mg beta decay have been measured with high precision. The latter depended on gamma-ray intensities being measured with an HPGe detector calibrated for relative efficiencies to an unprecedented 0.15%. Previous precise measurements of 0+ --> 0+ transitions have been restricted to the nine that populate stable daughter nuclei. No more such cases exist, and any improvement in a critical Cabibbo-Kobayashi-Maskawa unitarity test must depend on precise measurements of more exotic nuclei. With this branching-ratio measurement, we show those to be possible for T(z)=-1 parents. We obtain a corrected Ft value of 3071(9) s, in good agreement with expectations.

Measurement of the 20 and 90 keV resonances in the 18O(p,alpha)15N reaction via the Trojan horse method.

The

Enhanced production of neutron-rich rare isotopes in peripheral collisions at Fermi energies.

^{18}{\rm O}(p,\alpha)^{15}{\rm N}

Measurement of the 20 and 90 keV resonances in the

reaction is of primary importance in several astrophysical scenarios, including fluorine nucleosynthesis inside AGB stars as well as oxygen and nitrogen isotopic ratios in meteorite grains. Thus the indirect measurement of the low energy region of the

{}^{18}{\rm O}(p,\alpha){}^{15}

^{18}{\rm O}(p,\alpha)^{15}{\rm N}