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Analyzing powers for the {sup 9}Be({rvec p},{gamma}){sup 10}B reaction were measured by stopping a 100 keV polarized proton beam in a {sup 9}Be target. The measured vector analyzing power is A{sub y}(90{degree})=0.18{plus_minus}0.03 for capture to the ground state, with smaller values at 90{degree} for the first three excited states. Astrophysical S factors were calculated for each of the final states using a direct capture plus resonance model which fit both the present analyzing power data and the previously reported cross section data. The calculated S factors at E{sub p}=0 keV for capture to the ground state and first three excited states were 0.25, 0.34, 0.27, and 0.10 keV b, respectively, which are considerably smaller than previously reported. The observed analyzing powers are explained, within experimental uncertainty, as arising from the interference of the E1 direct capture amplitude with the tails of nearby p-wave and s-wave resonances. {copyright} {ital 1998} {ital The American Physical Society}

Data obtained from studies of the $p(d\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{3}\mathrm{He}$ and the $d(p\ensuremath{\rightarrow},\ensuremath{\gamma}{)}^{3}\mathrm{He}$ reactions have been used to extract the transition amplitudes corresponding to $S=1/2$ (doublet) and $S=3/2$ (quartet) $M1$ radiative capture. Protons (deuterons) of 40 keV (80 keV) were stopped in ${\mathrm{D}}_{2}\mathrm{O}$ $({\mathrm{H}}_{2}\mathrm{O})$ ice targets. Angular distributions of $\ensuremath{\sigma}$, ${A}_{y},$ ${T}_{20},$ ${P}_{\ensuremath{\gamma}}$, and ${\mathrm{iT}}_{11}$ were fit simultaneously in terms of the four possible $E1$ $p$-wave capture amplitudes and the two $(S=1/2$ and $3/2)$ possible $M1$ $s$-wave capture amplitudes. The results obtained at ${E}_{\mathrm{cm}}=23.3$ keV indicate that the $S=1/2$ $M1$ capture cross section is 13.77 $\ifmmode\pm\else\textpm\fi{}$ 0.66 nb, while the $S=3/2$ $M1$ capture cross section is 6.74 $\ifmmode\pm\else\textpm\fi{}$ 0.44 nb. These results agree with the predictions of a recent three-body theoretical calculation which includes two-body currents [e.g., meson-exchange currents (MEC's)]. They also agree with the previous experimental determination of the doublet and quartet fusion rates obtained using the Wolfenstein-Gerstein effect to vary the relative population of $S=1/2$ and $3/2$ nuclear spins in the $\ensuremath{\mu}$-$p$-$d$ molecule prior to fusion.

New measurements of the analyzing powers ${A}_{y}$ and ${T}_{20}$ have been obtained for the $^{2}\mathrm{H}(d,\ensuremath{\gamma})^{4}\mathrm{H}\mathrm{e}$ reaction at a laboratory beam energy of $115\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. A transition matrix element analysis results in a unique solution which indicates that the reaction proceeds by 55% $E2$, 29% $E1$, and 16% $M2$ radiation. These results are shown to be in good agreement with the results of a new refined resonating group model calculation. The impact of these results on the extrapolated value of the astrophysical $S$ factor for this reaction is discussed.

The ${}^{11}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{p},\ensuremath{\gamma}{)}^{12}\mathrm{C}$ reaction was studied by measuring the $\ensuremath{\gamma}$ rays that were produced when 80--100-keV polarized protons were stopped in a thick ${}^{11}\mathrm{B}$ target. Cross sections and vector analyzing powers at $90\ifmmode^\circ\else\textdegree\fi{}$ were determined as a function of energy for capture to the ground and first excited states of ${}^{12}\mathrm{C}.$ These analyzing powers are particularly sensitive to the interference between s- and p-wave contributions, and to the relative phase between direct and resonance amplitudes. The results were used to produce a reliable extrapolation of the astrophysical S factor at 0 keV by means of a direct-capture-plus-resonances model calculation. The value of $S(0)$ that was obtained for ${}^{11}\mathrm{B}(p,{\ensuremath{\gamma}}_{0}),$ $1.8\ifmmode\pm\else\textpm\fi{}0.4 \mathrm{keV}\mathrm{}\mathrm{b},$ is in agreement with previously determined values, but for ${}^{11}\mathrm{B}(p,{\ensuremath{\gamma}}_{1})$ the value of $S(0)$ is $3.5\ifmmode\pm\else\textpm\fi{}0.6 \mathrm{keV}\mathrm{}\mathrm{b}$ and is more than twice as large as previously determined values.

The first measurement of the ${}^{2}\mathrm{H}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},n)p$ analyzing power near threshold has been performed using the High-Intensity Gamma-ray Source (HIGS) at the Duke Free-Electron Laser Laboratory. A 3.58 MeV $\ensuremath{\gamma}$-ray beam having an energy resolution of $2.5%$ and $100%$ linear polarization was incident on an active ${\mathrm{C}}_{6}{\mathrm{D}}_{12}$ target. Outgoing neutrons were detected parallel and perpendicular to the plane of $\ensuremath{\gamma}$-ray polarization at a lab angle of 150\ifmmode^\circ\else\textdegree\fi{}. The experimentally determined analyzing power provides a sensitive measurement of the relative $E1$ and $M1$ contributions to the total cross section.

We have performed a measurement of the cross section for the ${}^{4}\mathrm{He}(\ensuremath{\gamma},dd)$ reaction with photon energies between 150 and 250 MeV. Both reaction particles were detected in coincidence. We obtained absolute cross sections at six angles and two energy bins (150\char21{}190 MeV and 190\char21{}250 MeV). A Legendre polynomial fit to the angular distribution shows a ${\mathrm{sin}}^{2}\ensuremath{\theta}$ distribution which suggests the isospin-forbidden $E1$ transition. However, a transition matrix element (TME) analysis using only strictly allowed transitions shows that the angular distribution can be described by just two TMEs: $E2$ s- and d-wave absorption on the D state of ${}^{4}\mathrm{He}.$ We performed an inverse direct-capture calculation in order to determine if the D state could contribute to such a high degree to the cross section. This calculation indicates that 90% of the cross section arises from absorption on the D state but fails to reproduce the observed ${\mathrm{sin}}^{2}\ensuremath{\theta}$ angular distribution.

Measurements of the cross section, vector and tensor analyzing powers, and linear gamma-ray polarization in the radiative capture reactions $D(p,\ensuremath{\gamma}{)}^{3}\mathrm{He}$ and $p(d,\ensuremath{\gamma}{)}^{3}\mathrm{He}$ at c.m. energies in the range 0--53 keV allow the determination of the reduced matrix elements (RMEs) relevant for these transitions. From these RMEs the value of the integral which determines the Gerasimov-Drell-Hearn sum rule for ${}^{3}\mathrm{He}$ is obtained in the threshold region, corresponding to two-body breakup, and compared with the results of an ab initio microscopic three-body model calculation. The theoretical predictions for the value of this integral based on a ``nucleons-only'' assumption are an order of magnitude smaller than experiment. The discrepancy is reduced to about a factor of 2 when two-body currents are taken into account. This factor of 2 is due to an almost exact cancellation between the dominant $E1$ RMEs in the theoretical calculation. The excess $E1$ strength observed experimentally could provide useful insights into the nuclear interaction at low energies.