Y.-W. Lui

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}

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 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.

Continuous distribution of αt relative kinetic energies in 7Li breakup reactions

Abstract A newly developed technique has been used to probe a previously inaccessible region of the continuum in the at channels of 7 Li breakup reactions. This was used to investigate reactions of 63 MeV 7 Li with 58 Ni, 120 Sn, 144 Sm, and 208 Pb targets. Breakup pairs of α-particles and tritons emitted within a finite opening angle were analyzed according to their magnetic rigidity using a K = 150 Enge split-pole spectrograph. The αt coincidences were taken with two single-wire proportional counters mounted at different positions along the focal plane of the spectrograph. The large energy acceptance ( E max / E min ≈ 8) of the spectrograph is crucial to the present coincidence measurements involving two particles with different q / m values. Very small relative energy components were studied without any detection threshold. A pronounced bump was observed immediately above the αt particle threshold. No strong indication of the post Coulomb acceleration was observed. The excitation of the continuum states as well as the 7 − 2 state in 7 Li is discussed in terms of the distorted-wave Born approximation. The astrophysical implications of the data are also discussed regarding the Coulomb excitation of the continuum. The present technique offers the promise of very high sensitivity at small relative energies if it were applied in conjunction with ray-tracing, a thin target, and a dispersion-matched beam.

FAUST : A NEW FORWARD ARRAY DETECTOR

A new forward array has been designed and constructed using silicon technology. The detectors telescopes are Si followed by CsI that are read out by photodiodes. This combination allows for isotopic resolution through Z = 6. The special edge-mounting of the silicon detector combined with the ring-like structure of the overall array has allowed for a design that minimizes dead area.

Isoscalar giant resonances in Ca 48

The giant resonance region from 9.5 MeV < E{sub x} < 40 MeV in {sup 48}Ca has been studied with inelastic scattering of 240-MeV {alpha} particles at small angles, including 0 deg. 95{sub -15}{sup +11}% of E0 energy-weighted sum rule (EWSR), 83{sub -16}{sup +10}% of E2 EWSR, and 137 {+-} 20% of E1 EWSR were located below E{sub x}=40 MeV. A comparison of the experimental data with calculated results for the isoscalar giant monopole resonance, obtained within the mean-field-based random-phase approximation, is also given.

Alpha particle optical potentials at 240 MeV

Abstract Elastic and inelastic scattering of 240 MeV alpha particles on 58 Ni, 116 Sn and 197 Au have been studied. Optical potentials were obtained and are consistent with results at other beam energies. The inelastic scattering differential cross sections for the 1.454 MeV 2 + and 4.475 MeV 3 − states in 58 Ni and the 1.294 MeV 2 + and 2.266 3 − states in 116 Sn were fit well with DWBA calculations using deformation lengths from other works.

Observation of α-t continuum states with relative energies of 0–2 MeV in7Li breakup reactions

Abstract The breakup of 7 Li at 63 MeV was studied in an α-t coincidence experiment using an Enge split pole spectrograph. For the first time, the entire spectrum of the α-t continuum states of 7 Li was observed in the range of the relative energy ɛ from zero to 2 MeV. A pronounced bump was found at ɛ ≈ 0.4MeV. The astrophysical implications of the data are discussed.

Strongly-suppressed post-Coulomb acceleration in non-resonant breakup of 7Li

Abstract Cross sections were measured at energies of astrophysical relevance for the non-resonant breakup of 42 MeV– 7 Li by 6 targets. It was found that post-acceleration of the α and the triton in the target Coulomb field is vanishingly small, independent of the target nucleus, compared to that for prompt breakup. The transition probabilities were evaluated for the astrophysical continua in 7 Li which decay by tunneling through the Coulomb barrier. They are consistent with the present observations.

Asymptotic Normalization Coefficients for 13 C + p ! 14 N

The {sup 13}C({sup 14}N,{sup 13}C){sup 14}N proton exchange reaction has been measured at an incident energy of 162 MeV. Angular distributions were obtained for proton transfer to the ground and low-lying excited states in {sup 14}N. Elastic scattering of {sup 14}N on {sup 13}C also was measured out to the rainbow angle region in order to find reliable optical model potentials. Asymptotic normalization coefficients for the system {sup 13}C+p{r_arrow}thinsp{sup 14}N have been found for the ground state and the excited states at 2.313, 3.948, 5.106, and 5.834 MeV in {sup 14}N. These asymptotic normalization coefficients will be used in a determination of the {ital S} factor for {sup 7}Be(p,{gamma}){sup 8}B at solar energies from a measurement of the proton transfer reaction {sup 14}N({sup 7}Be,{sup 8}B){sup 13}C. {copyright} {ital 1998} {ital The American Physical Society}