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The48 Ca(γ,n) cross section was measured using γ-ray beams of energies between 9.5 and 15.3 MeV generated at the Triangle Universities Nuclear Laboratory (TUNL) high-intensity γ-ray source (HIγS). Prior to this experiment, no direct measurements had been made with γ-ray beams of sufficiently low energy spread to observe structure in this energy range. The cross sections were measured at thirty-four different γ-ray energies with an enriched 48 Ca target. Neutron emission is the dominant decay mechanism in the measured energy range that spans from threshold, across the previously identified M1 strength, and up the low-energy edge of the E1 giant dipole resonance (GDR). This work found B(M 1) = 6.8 ± 0.5 µ 2 N for the 10.23 MeV resonance, a value greater than previously measured. Structures in the cross section commensurate with extended random-phase approximation (ERPA) calculations have also been observed whose magnitudes are in agreement with existing data.

11A neutron counter designed for assay of radioactive materials has been adapted for beam exper-12 iments at TUNL. The cylindrical geometry and 60% maximum efficiency make it well suited for 13 (γ, n) cross-section measurements near the neutron emission threshold. A high precision charac-14 terization of the counter has been made using neutrons from several sources. Using a combination 15 of measurements and simulations, the absolute detection efficiency of the neutron counter was de-16 termined to an accuracy of ± 3% in the neutron energy range between 0.1 and 1 MeV. It is shown 17 that this efficiency characterization is generally valid for a wide range of targets.

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We present measurements of n-d analyzing power, A y (θ), at E n = 22.5 MeV. The experiment uses a shielded neutron source which produced polarized neutrons via the 2 H( d, n) 3 He reaction. It also uses a deuterated liquidscintillator center detector and six pairs of liquid-scintillator neutron side detectors. Elastic neutron scattering events are identified by using time-of-flight techniques and by setting a window in the center detector pulse-height spectrum. The beam polarization is monitored by using a high-pressure helium gas cell and an additional pair of liquid-scintillator side detectors. The n-d A y (θ) data were corrected for finite-geometry and multiple-scattering effects using a Monte Carlo simulation of the experiment. The 22.5-MeV data demonstrate that the three-nucleon analyzing power puzzle also exists at this energy. They show a significant discrepancy with predictions of highprecision nucleon-nucleon potentials alone or combined with Tucscon-Melbourne or Urbana IX three-nucleon forces, as well as currently available effective-field theory based potentials of next-to-next-to-next-to-leading order.

The first measurement of the three-body photodisintegration of longitudinally-polarized 3 He with a circularly-polarized γ-ray beam was carried out at the High Intensity γ-ray Source (HIγS) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contributions from the three-body photodisintegration to the 3 He GDH integrand are presented and compared with state-of-the-art three-body calculations at the incident photon energies of 12.8 and 14.7 MeV. The data reveal the importance of including the Coulomb interaction between protons in three-body calculations.PACS numbers: 24.70.+s, 25.10.+s, 25.20.Dc, 29.25.Pj, 29.27.Hj, 29.40.Mc, 67.30.ep The study of three-nucleon systems has long been of fundamental importance to nuclear physics [1,2]. Calculations using mainly the machinery of Faddeev [3] and Alt-Grassberger-Sandhas equations (AGS) [4] have been carried out for three-body systems using a variety of nucleon-nucleon (NN) potentials [5,6], and three-nucleon forces (3NFs) like Urbana IX (UIX) [8] or CD Bonn + ∆ [9], with the latter yielding an effective 3NF through the ∆-isobar excitation.Calculations for the three-body photodisintegration of 3 He with double polarizations have been carried out. The calculations by Deltuva et al. are based on AGS equations and employ the CD Bonn + ∆ potential [9] with the corresponding single-baryon and mesonexchange electromagnetic currents (MEC) plus relativistic single-nucleon charge corrections. The results are obtained using the computational technology of Ref. [10]. The proton-proton Coulomb force is included using the method of screening and renormalization [11]. Skibiński et al. solve the Faddeev equations by using the AV18 potential and the UIX 3NF [8] accounting for single nucleon currents and the two most important MEC, the seagull and pion-in-flight terms. Their results are obtained using the methods described in Ref. [12].Recent advances in high intensity polarized beams and polarized 3 He targets allow for tests of new spindependent observables predicted by theory. A polarized 3 He target is often used as an effective polarized neutron target to extract the electromagnetic form factors [13][14][15] and the spin structure functions [16] of the neutron since the nuclear spin of 3 He is carried mostly by the unpaired neutron. To acquire the information about the neutron using a polarized 3 He target, nuclear corrections relying on the state-of-the-art three-body calculations need to be validated by experiments. While data from electrodisintegration of polarized 3 He [17] were used to test three-body calculations [18], data from polarized photodisintegration of 3 He below the pion production threshold did not exist prior to this work.The spin-dependent total cross sections from the threebody photodisintegration of 3 He below pion production threshold are of further importance for the investigation of the Gerasimov-Drell-Hearn (GDH) sum rule [19]. The GDH sum rule relates the energy-weighted di...