M. Spraker

The B-10 (polarized-p, gamma) C-11 reaction at astrophysically relevant energies

The B-10(, gamma)C-11 reaction was studied by detecting the gamma-rays produced when 100, 130-, and 160-keV polarized protons were stopped in a thick B-10 target. Polarized and unpolarized incident beams were used to measure the cross section and vector analyzing power as a function of angle and energy for capture to the ground (J(pi)=3/2(-)), the second (E=4319 keV, J(pi)=5/2(-)), and the fifth (E=6478 keV, J(pi)=7/2(-)) excited states of C-11. The data were analyzed to obtain the amplitudes and phases of the contributing transition-matrix elements at each measured energy for all three transitions. Values of the astrophysical S factors were obtained from the cross section data and are compared to previous results. A direct capture plus resonance model calculation was performed in an attempt to account for all measured quantities. It was found that the large (similar to32%) value of A(y)(90degrees) observed in the case of capture to the ground state could be accounted for by including the subthreshold resonance at 8420 keV.

Compton scattering of polarized {gamma} rays by {sup 16}O for E{sub {gamma}}=25-40 MeV

Measurements of the polarization asymmetries {sigma}({theta}{sub c.m.}) and {sigma}(E{sub {gamma}}) of Compton scattering by {sup 16}O have been performed in the energy range of 25-40 MeV over a range of scattering angles between 90 and 150 deg. . An analysis of the present data combined with previous results indicates that significant, narrow concentrations of E2 strength are not present below an excitation energy of 40 MeV. The existence, however, of a broad isovector giant quadrupole resonance exhausting a large percentage of the isovector energy weighted sum rule is not ruled out by the combined data. Additionally, the present data are insensitive to modifications to the free values of the nucleon polarizabilities, but cannot rule them out.

The {sup 7}Li(d-vector,n{sub 0}){sup 8}Be and {sup 7}Li(d-vector,n{sub 1}){sup 8}Be reactions below 160 keV

The polarization observables have been determined for the {sup 7}Li(d-vector,n{sub 0}){sup 8}Be and {sup 7}Li(d-vector ,n{sub 1}){sup 8}Be reactions at beam energies between 80 and 160 keV. A Transition Matrix Element (TME) analysis revealed unique, dominant p-wave solutions for both neutron channels. The polarization observables were compared with distorted wave Born approximation (DWBA) and coupled reaction channels (CRC) calculations. The general features of the data can be reproduced by the CRC calculations when a large target spin-orbit interaction is included. However, serious discrepancies are observed when the TMEs of the theory and experiment are compared.

The Li-7((d)over-right-arrow, n(0))Be-8 and Li-7((d)over-right-arrow, n(1))Be-8 reactions below 160 keV

The polarization observables have been determined for the Li-7(d,n(0))Be-8 and Li-7(d,n(1))Be-8 reactions at beam energies between 80 and 160 keV. A Transition Matrix Element (TME) analysis revealed unique, dominant p-wave solutions for both neutron channels. The polarization observables were compared with distorted wave Born approximation (DWBA) and coupled reaction channels (CRC) calculations. The general features of the data can be reproduced by the CRC calculations when a large target spin-orbit interaction is included. However, serious discrepancies are observed when the TMEs of the theory and experiment are compared.