S. O. Nelson

The B-10((p)over-right-arrow, 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.

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.

Evaluations of thermonuclear proton capture reaction rates for 2 H, 7 Li, 9 Be, and 11 B

Abstract Recent measurements and analyses of proton induced radiative-capture reactions in the vicinity of E p =100 keV performed at the Triangle Universities Nuclear Laboratory are used to calculate the thermonuclear reaction rates of relevance in astrophysical plasmas for the reactions: D(p, γ ) 3 He, 7 Li(p, γ 0,1 ) 8 Be, 9 Be(p, γ 0,1,2,3 ) 10 B, and 11 B(p, γ 0,1 ) 12 C. Higher energy data from previous measurements were included when possible. The Maxwellian-averaged reaction rates, obtained using numerical integration techniques, are presented in tabular form as a function of temperature. Capture to the ground and excited states are treated separately, thus allowing the determination of inverse reaction rates for specified target states. The high temperature cut-offs of the reaction rate calculations are discussed. The results are compared to those presented in the recent NACRE compilation, where appropriate, and new analytical approximations for the total reaction rates are presented in a standard form.

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.