R. M. Prior

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.

Observation of p-wave capture strength in the 2H(d, γ)4He reaction at Ed= 80−0 keV

Abstract The 2 H ( d , γ 4 He reaction has been studied using tensor polarized deuterons having an incident energy of E d (lab) = 80 keV, which were stopped in the target. The angular distributions of the cross section σ ( θ )/ A 0 , vector analyzing power A y ( θ ), and tensor analyzing power A yy ( θ ) were measured and were interpreted using a model independent transition-matrix element analysis. These results lead to the conclusion that over 50% of the cross section strength at these low energies is due to p-wave E1 and M2 capture, is sharp contrast to previous assumptions of dominant s-wave E2 capture.

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.

Astrophysical S factor for the {sup 7}Li(d,n{sub 0}){sup 8}Be and {sup 7}Li(d,n{sub 1}){sup 8}Be reactions

The absolute astrophysical S factor and cross section for the {sup 7}Li(d,n{sub 0}){sup 8}Be and {sup 7}Li(d,n{sub 1}){sup 8}Be reactions have been determined using deuteron beams with energies between 45 and 80 keV. The slope of the S factor is consistent with zero in the n{sub 0} case but is slightly negative in the n{sub 1} case. The S factor for the sum of both neutron groups at c.m. energies below 70 keV is S(E)=5400({+-}1500)-37({+-}21)E keV b, where E is the c.m. energy in keV.

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.

Effects of non-nucleonic degrees of freedom in the {ital D}({ital p{searrow}{bold ,}}{bold {gamma}}){sup {bold 3}}{ital H}{ital e} and {ital p}({ital d{searrow}{bold ,{gamma}}}{bold )}{sup {bold 3}}{ital H}{ital e} reactions

Measurements of the D({ital p}{searrow},{gamma}){sup 3}He and {ital p}({ital d}{searrow},{gamma}){sup 3}He reactions below {ital E}{sub {ital p},{ital d}}=80 keV are compared to the results of calculations based on correlated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and a nuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interaction currents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an {ital S}-factor value of {ital S}({ital E}=0)=0.165{plus_minus}0.014 eVb, in reasonable agreement with theory. {copyright} {ital 1996 The American Physical Society.}Measurements of the D(p-->, gamma )3He and p(d-->, gamma )3He reactions below Ep,d = 80 keV are compared to the results of calculations based oncorrelated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and anuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interactioncurrents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an S-factor value of S(E= 0) = 0.165z0.014 eV b, in reasonable agreement with theory.

Effects of non-nucleonic degrees of freedom in the D(p

Measurements of the D({ital p}{searrow},{gamma}){sup 3}He and {ital p}({ital d}{searrow},{gamma}){sup 3}He reactions below {ital E}{sub {ital p},{ital d}}=80 keV are compared to the results of calculations based on correlated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and a nuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interaction currents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an {ital S}-factor value of {ital S}({ital E}=0)=0.165{plus_minus}0.014 eVb, in reasonable agreement with theory. {copyright} {ital 1996 The American Physical Society.}Measurements of the D(p-->, gamma )3He and p(d-->, gamma )3He reactions below Ep,d = 80 keV are compared to the results of calculations based oncorrelated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and anuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interactioncurrents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an S-factor value of S(E= 0) = 0.165z0.014 eV b, in reasonable agreement with theory.

Effects of Non-nucleonic Degrees of Freedom in theD(p→,γ)H3eandp(d→,γ)H3eReactions

Measurements of the D({ital p}{searrow},{gamma}){sup 3}He and {ital p}({ital d}{searrow},{gamma}){sup 3}He reactions below {ital E}{sub {ital p},{ital d}}=80 keV are compared to the results of calculations based on correlated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and a nuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interaction currents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an {ital S}-factor value of {ital S}({ital E}=0)=0.165{plus_minus}0.014 eVb, in reasonable agreement with theory. {copyright} {ital 1996 The American Physical Society.}Measurements of the D(p-->, gamma )3He and p(d-->, gamma )3He reactions below Ep,d = 80 keV are compared to the results of calculations based oncorrelated hyperspherical harmonic wave functions obtained from realistic interactions with full inclusion of Coulomb distortion in the initial continuum state, and anuclear current operator with one- and two-body components. Dramatic effects due to the tensor force and the associated two-body (meson-exchange) interactioncurrents are observed in the vector and, to some extent, tensor analyzing powers for the first time. The extrapolation to zero energy leads to an S-factor value of S(E= 0) = 0.165z0.014 eV b, in reasonable agreement with theory.

A polarimeter for low-energy protons

Abstract A polarimeter is described for proton beam energies below 100 keV using the 7 Li(p, γ) 8 Be reaction. Measurements indicate an analyzing power near 0.4 with yields that would allow a 10% measurement of beam polarization in 1 h for sources producing beam currents on the order of 30 μA.