[en] The ²H(d,γ)⁴He reaction is expected to be dominated by electric quadrupole (E2) s-wave (ell = 0) capture to the D-state (ell = 2) of ⁴He below E_d (lab) = 500 keV, where the centrifugal barrier should suppress the electric quadrupole (E2) d-wave (ell = 2) capture to the S-state (ell = 0). Enhancement of the total cross section below E_d (lab) = 500 keV has been attributed to this mechanism, although no direct evidence exists to support this claim. To investigate this issue, the author has measured the vector and tensor analyzing powers of the ²H(d,γ)⁴He reaction using an 80 keV beam of polarized deuterons. Results are presented for the vector and tensor analyzing powers A_y(θ) and A_yy(θ) and the differential cross section σ(θ)/A₀ for E_d(lab) = 80 - 0 keV at θ_c.m. = 0 degrees, 45 degrees, and 82 degrees. A model-independent transition matrix element analysis of the data finds that a major portion of the capture strength results from electric dipole (E1) and magnetic quadrupole (M2) p-wave capture (ell = 1). The data are also compared to a recent microscopic coupled-channel resonating group model calculation which includes electric quadrupole (E2), electric dipole (E1), magnetic quadrupole (M2), and magnetic dipole (M1) transitions and the coupled deuteron-deuteron, proton-triton, and neutron-³He channels. The model produces fair agreement with the experimental data when a semi-realistic force is used

[en] An internal polarized ³He target is currently under construction at MIT. The target will be used in the HERMES experiment, which will measure the spin dependent deep inelastic scattering from the neutron and proton by the scattering of 30-35 GeV longitudinally polarized electrons from polarized hydrogen, deuterium, and ³He in the East Hall of HERA. The target is based on the technique of metastability exchange laser optical pumping. ³He nuclei are introduced into a glass cell, where they are polarized with high intensity laser light. The nuclei then migrate out of the glass cell into a windowless storage cell where they are allowed to interact with the beam before being pumped away. Two pairs of Helmholtz coils will be employed to create a magnetic field which will orient the ³He nuclei along one of two axes. The storage cell will be cryogenically cooled to 15K, giving a density of 10¹⁵ atoms/cm². Target polarizations of over 50% are expected. The present status of the HERMES target will be discussed

[en] Polarized proton capture experiments have been performed in an attempt to observe the Isovector Giant Quadrupole Resonance (IVGOR) in ⁹⁰Zr. The cross section and vector analyzing power for transitions to the ground and low-lying states in the ⁸⁹Y(p, γ)⁹⁰Zr reaction have been studied over the angular range over the energy range E_p = 18.5-28.5 MeV (at θ_γ = 90 degrees). A transition-matrix element analysis of the γ₀E2 and E3 radiation, suggests a pure direct capture calculation predicts only 6% E2 strength. The A_y(E) data at 90 degrees for the γ₁₊₂₊₃ transitions (ie. to the first three strong single-particle excited states) depicts a resonance-like structure near ED = 23 MeV. These data are adequately described using the direct-semidirect (DSD) model by including IVGQ resonances at E_GQR = 29.0 MeV built on each of the three states, with widths of E_GQR = 5.5 MeV and strengths which exhaust 100% of the isovector E2 energy-weighted sum rule for each state. This same DSD calculation predicts a resonance structure in the γ₀ analyzing power near E_p = 21 MeV, which is not seen in the data

[en] This paper reports the measurement of superratio for inelastic pion scattering. The measured spectrum for pion-plus helium-3 scattering is given

[en] We describe an internal polarized ³He target under construction which will be used in several electron storage ring experiments. The target is based on the technique of metastability exchange laser optical pumping, where the polarized atoms flow into a cryogenically-cooled storage cell. This novel technique allows for high precision measurements where the beam interacts with the pure atomic species. Both the HERMES experiment at DESY and the BLAST detector at the MIT Bates Laboratory will use the polarized ³He target in their measurements. Details of the target system, including the provisions needed to incorporate the target into the electron storage ring, are presented

[en] The ³⁰Si(rvec p,γ)³¹P reaction has been studied in the energy range E_p = 20-36 MeV. A transition matrix element analysis of σ(θ) and σ(θ)A_y(θ) at E_p = 25.5 MeV reveals substantial E2 strength (σ_E2/σ_tot ∼ 26%) in the (p,γ₁) channel, in excess of a direct E2 capture estimate (∼7%). The energy dependence of A_y(90 degree) for γ₁ shows a resonance structure which can be reproduced by a direct-semidirect calculation including an E2 resonance (E_IVGOR = 38.6 MeV Γ_IVGOR = 5.0 MeV, S_IVGOR = 50%) at the expected peak of the isovector giant quadrupole resonance built on the first excited state of ³¹P. Angular distributions of σ(θ) and σ(θ)A_y(θ) have also been obtained for the ⁸⁹Y(rvec p,γ)⁹⁰Zr reaction at E_p = 22.5 MeV. A preliminary analysis reveals large E2 contributions (∼28%) for the γ₀ transition, as well as possible E3 strength

[en] The ³⁰Si(rvec p,γ)³¹P reaction has been studied in the proton energy range E_p=20--36 MeV. Angular distributions of the cross section and the analyzing power have been measured for γ-ray transitions to the ground state and the first excited state of ³¹P over the angular range 37.5 degree--145 degree at E_p=25.5 MeV. Legendre polynomial fits to both observables yield nonzero coefficients of order k=3,4, suggesting the interference of E2 radiation with the dominant E1 radiation. A transition-matrix-element analysis of the data indicates that ∼26% of the γ₁ cross section at this energy arises from E2 radiation, whereas only 10% of the γ₀ cross section can be attributed to E2 radiation. Direct-semidirect calculations give a direct E2 component of ∼7% for both channels, suggesting significant excess E2 strength in the γ₁ channel at this energy. The energy dependence of the 90 degree analyzing power for γ₁ shows a resonance structure near E_p=34 MeV which can be reproduced by a direct-semidirect calculation including an E2 resonance at E_GQR=38.6 MeV with a width of Γ_GQR=5.0 MeV and a strength of 50% of the isovector E2 energy-weighted sum rule. The current results thus provide strong evidence for collective E2 strength roughly at the expected peak of the isovector giant quadrupole resonance built on the first excited state of ³¹P

[en] The absolute differential cross section for the ³H(p,γ)⁴He reaction has been measured at θ_γ=90 degree for E_p=2.0--15.0 MeV, corresponding to photon energies E_γ=21.3--31.1 MeV. The present results are 35% lower than previously measured (p,γ) cross sections and are in excellent agreement with recent (γ,p) data obtained with monoenergetic photons. Comparing our results to current photoneutron cross sections gives a ratio σ(γ,p)/σ(γ,n)=1.09±0.17 for E_γ=24--31 MeV. This ratio is consistent with conventional theoretical predictions, indicating that no charge-symmetry violation in ⁴He is required

[en] The cross section and vector analyzing power for transitions to the ground and low-lying states in the ⁸⁹Y(rvec p,γ)⁹⁰Zr reaction have been studied over the angular range θγ=38.8 degree--130 degree at E_p=22.5 MeV and over the energy range E_p=18.5--28.5 MeV at θ_γ=90 degree. Angular distributions for the γ₀ and γ₁₊₂₊₃ transitions (i.e., to the first three strong single-particle excited states) reveal large asymmetries about θ_γ=90 degree in both σ(θ) and σ(θ)A_y(θ), suggesting E1/E2 interference effects. Legendre polynomial fits to these data yield nonzero coefficients of order k=3,4, thus confirming interference between the dominant E1 radiation and opposite parity E2 radiation. A transition-matrix element analysis of the γ₀ angular distribution data, including E1 and E2 radiation, suggests a 28% E2 contribution, while a pure direct capture calculation predicts only 12% E2 strength. The energy dependence of A_y(90 degree) for the γ₁₂₃ data is adequately described using the direct-semidirect model by including isovector quadropole resonances at E_GQR=27.5 MeV, built on each of the three states, with widths of Γ_GQR=7.0 MeV and strengths which exhaust 100% of the isovector E2 energy-weighted sum rule for each state. These results provide strong evidence for collective E2 strength built on excited states in ⁹⁰Zr, approximately at the energy predicted for the isovector giant quadrupole resonance, but are inconclusive concerning the ground-state transition

[en] We have measured the widths of the 3/2^- ground states of ⁵He and ⁵Li using the ³H(d,γ)⁵He and the ³He(d,γ)⁵Li reactions at E_d=8.6 MeV. The γ-ray spectra were fitted with a convolution of the NaI line-shape response function, as measured with the ³H(p,γ)⁴He reaction, and a Breit-Wigner single-level expression. The widths extracted from the spectra were found to be Γ_n=1.36±0.19 MeV for ⁵He, and Γ_p=2.44±0.21 MeV for ⁵Li. These values, significantly different from previously quoted measurements, lead to reduced widths which are equal to within error, a result which is consistent with the charge-symmetry property of the nuclear force