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Data on the light output response of BC-505 liquid scintillator to neutrons ranging in energy from 0.5 to 12 MeV have been fitted with the parameterization of Chou using the GEANT4 toolkit to simulate the response of the scintillators. Excellent agreement is obtained with the parameters kB = 0.0061 ± 0.0003 g cm - 2 MeV - 1 and C = ( 1.0 ± 0.1 ) × 10 - 5 g 2 cm - 4 MeV - 2 .

Differential cross sections for the $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}n$ reaction have been measured at photon energies 1 to 2 MeV above threshold using tagged-photon beams. The electric dipole amplitude ${E}_{0+}$ deduced at threshold is compared to recent predictions from chiral perturbation theory. Constraints on the value of the $\ensuremath{\pi}N$ coupling constant are inferred by combining theory and experiment.

A segmented neutron detector has been constructed and used for recoil neutron (6–13 MeV) measurements of the reaction γp→nπ+ very close to threshold. BC-505 liquid scintillator was used to allow pulse shape discrimination between neutrons and photons. A measurement of the absolute efficiency of the detector was performed using stopped pions in the reaction π−p→nγ. Results of the efficiency calibration are compared to a Monte Carlo simulation.

Cross sections have been measured for the {sup 3}He({gamma},{ital pp}){ital n} reaction with tagged photons in the range {ital E}{sub {gamma}} =161{endash}208 MeV using the Saskatchewan-Alberta Large Acceptance Detector (SALAD). The protons were detected over a range of polar angles of 40{degree}{endash}140{degree} and azimuthal angles of 0{degree}{endash}360{degree} with an energy threshold of 40 MeV. Comparisons are made with a microscopic calculation which includes one-, two-, and three-nucleon absorption mechanisms. One- and two-nucleon processes, including final-state interactions, are unable to account for the measured cross sections. The addition of three-nucleon absorption diagrams gives roughly the right strength, but the distribution in phase space is in disagreement with the data. {copyright} {ital 1996 The American Physical Society.}

Inclusive {sup 12}C({gamma},{ital pp}) cross sections have been measured with tagged photons in the range {ital E}{sub {gamma}}=187{endash}227 MeV using the Saskatchewan-Alberta Large Acceptance Detector (SALAD). The large angular acceptance allowed the measurement of noncoplanar {ital pp} emission. The cross sections were compared to a Monte Carlo intranuclear cascade calculation. Agreement was reasonable for the shapes of the cross sections but the calculated total cross section was 3.9 times larger than the data. {copyright} {ital 1996 The American Physical Society.}

Data on the absolute light output L(E) of plastic scintillator, in equivalent electron energy, to protons with energies up to 20 MeV have been fitted with the parameterization L(E)=A ∞ 0 R In +α dE dx where E is the initial particle energy, d E d x is the specific energy loss, R is the particle range, and α is the only free parameter. The scaling factor A has been expressed in terms of α and the specific energy loss for a minimum ionizing particle, producing an absolute response curve. The best-fit value was determined to be α = (0.025±0.002) g cm−2MeV−1 which gives a normalization of A = 41.0 MeV/(g/cm2). The results of the parameterization were compared with absolute response data for protons up to 150 MeV, and deuterons up to 120 MeV, with excellent agreement being observed.

Charge symmetry breaking in np elastic scattering at 347 MeV has been measured with high precision. From fits of the measured asymmetry curves over the angular range 53.4{degree} {le} {theta}{sub cm} {le} 86.9{degree}, the difference in the center-of-mass zero-crossing angles of the analyzing powers was determined to be 0.438{degree} {+-} 0.054{degree} (stat.) {+-} 0.051{degree} (syst.). Using the experimentally determined slope of the analyzing power, dA/d{theta} = ({minus}1.35 {+-} 0.05) {times} 10{sup {minus}2} deg{sup {minus}1}, this is equivalent to {Delta}A = [59 {+-} 7(stat.) {+-} 7(syst.) {+-} 2(syst.)] {times} 10{sup {minus}4}. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with this result.

The reaction cross section for [sup 3]He([gamma],[ital pd]) has been measured using the Saskatchewan-Alberta Large Acceptance Detector (SALAD) with tagged photons in the energy range from 166 to 213 MeV. The energy and angle of the proton and the deuteron were measured with SALAD while the tagger determined the photon energy. Differential cross sections have been determined for 40[degree][lt][theta][sub [ital p]][sup *][lt]150[degree]. The results are in agreement with the Bonn and Saclay photodisintegration measurements. The most recent photodisintegration measurement performed at Bates is higher by a factor of 1.3, which is just within the combined errors of the experiments. The proton capture results differ by a factor of 1.7 from the present experiment. Comparisons are made with microscopic calculations of the cross sections.

At TRIUMF we are measuring charge symmetry violation in np elastic scattering. If charge symmetry holds the analyzing powers A n and A p are equal. The measurements will therefore determine the difference from zero of ΔA ≡ A n − A p . The measurements are carried out in the vicinity where the analyzing powers cross zero in order to minimize systematic errors. A 350 MeV polarized ( P n ≅ 0.5) or unpolarized neutron beam is incident onto respectively an unpolarized or polarized ( P p ≅ 0.65) target of the butanol frozen spin type. A symmetric (about the beam axis and in the scattering plane) system of proton detectors and neutron arrays records neutron-proton coincidence events. The detection system allows measurements in the centre-of-mass angular range of 50°–90°.

The Saskatchewan-Alberta Large Acceptance Detector (SALAD) is a 4π detector designed and built for studies of photonuclear reactions with a tagged photon beam. The design and performance of the detector are described. Its characteristics have been studied by examining p-p elastic scattering with a proton beam at TRIUMF.

The two-body photodisintegration of He-3 has been investigated using tagged photons with energies from 14-31 MeV at MAX-lab in Lund, Sweden. The two-body breakup channel was unambiguously identified by the (nonsimultaneous) detection of both protons and deuterons. This approach was made feasible by the overdetermined kinematic situation afforded by the tagged-photon technique. Proton-and deuteron-energy spectra were measured using four silicon surface-barrier detector telescopes located at a laboratory angle of 90 degrees with respect to the incident photon-beam direction. Average statistical and systematic uncertainties of 5.7% and 6.6% in the differential cross section were obtained for 11 photon-energy bins with an average width of 1.2 MeV. The results are compared to previous experimental data measured at comparable photon energies as well as to the results of two recent Faddeev calculations which employ realistic potential models and take into account three-nucleon forces and final-state interactions. Both the accuracy and precision of the present data are improved over those obtained in the previous measurements. The data are in good agreement with most of the previous results, and favor the inclusion of three-nucleon forces in the calculations. (Less)

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.

The phenomenon of somatization, which results in unexplained physical complaints, is ubiquitous in primary care settings although it often goes unrecognized. Medical training emphasizes the identification and treatment of organic problems and may leave physicians unprepared to recognize and address somatoform complaints. As a process, somatization ranges from mild stress-related symptoms to severe debilitation. Patients at the low end of the spectrum often respond to simple reassurance, but patients who are more impaired require interventions specifically designed to avoid unnecessary exposure to dangerous, costly and frustrating diagnostic procedures and treatments.

The total photofission cross sections for the actinide nuclei ${}^{232}\mathrm{Th},$ ${}^{233}\mathrm{U},$ ${}^{235}\mathrm{U},$ ${}^{238}\mathrm{U},$ and ${}^{237}\mathrm{Np}$ have been measured from 68 to 264 MeV using tagged photons at the Saskatchewan Accelerator Laboratory. The fission fragments were detected using parallel-plate avalanche detectors. The results show that the fission probability for ${}^{238}\mathrm{U}$ is 20% lower than that for ${}^{237}\mathrm{Np}$ and 40% higher than that for ${}^{232}\mathrm{Th}.$ Less significant differences were also found among the individual uranium isotopes. These results contradict the assumption that the fission probability for ${}^{238}\mathrm{U}$ is approximately equal to unity in this energy range. It has also been observed that the fission probability as a function of energy for all these isotopes is constant, with the exception of that for ${}^{232}\mathrm{Th},$ which increases with energy, although it seems to be reaching a saturation value. Comparison between the total photofission cross section for ${}^{237}\mathrm{Np}$ and the photoabsorption cross sections for lighter nuclei shows a behavior consistent with a broadening of the $\ensuremath{\Delta}$ resonance with increasing atomic mass.

Cross sections for elastic Compton scattering from the deuteron were measured over the laboratory angles 35-150 deg. Tagged photons in the laboratory energy range 84-105 MeV were scattered from liquid deuterium and detected in the large-volume Boston University NaI (BUNI) spectrometer. Using the calculations of Levchuk and L'vov, along with the measured differential cross sections, the isospin-averaged nucleon polarizabilities in the deuteron were estimated. A best-fit value of (alpha-beta) = 2.6+/-1.8 was determined, constrained by dispersion sum rules. This is markedly different from the accepted value for the proton of (alpha-beta) = 10.0+/-1.5+/-0.9., Comment: 4 pages, 3 figures, accepted in Physical Review Letters; final version, discussion slightly modified, reference added

Elastic photon scattering cross sections on {sup 16}O have been measured in the energy range 27{endash}108 MeV. These data are inconsistent with a conventional interpretation in which the electric and magnetic polarizabilities of the bound nucleon are unchanged from the free values and the meson-exchange seagull amplitude is taken in the zero-energy limit. Agreement with the data can be achieved by invoking either strongly modified polarizabilities or a substantial energy dependence to the meson-exchange seagull amplitude. It is argued that these seemingly different explanations are experimentally indistinguishable and probably physically equivalent. {copyright} {ital 1996 The American Physical Society.}

TRIUMF Experiment 369, a measurement of charge symmetry breaking in np elastic scattering at 350 MeV, has completed data taking. Scattering asymmetries were measured with a polarized (unpolarized) neutron beam incident on an unpolarized (polarized) frozen spin target. Coincident scattered neutrons and recoil protons were detected by a mirror symmetric detection system in the center‐of‐mass angle range from 50°–90°. A preliminary result for the difference of the zero‐crossing angles, where analyzing powers cross zero, is Δθcm =0.445°±0.054°(stat.)±0.051°(syst.) based on fits over the angle range 53.4°≤θcm≤86.9°. The difference of the analyzing powers ΔA≡An−Ap, where the subscripts denote polarized nucleons, was deduced with dA/dθcm=(−1.35±0.05)×10−2 deg−1 to be [60±7(stat.)±7(syst.)±2(syst.)] ×10−4.

TRIUMF experiment 369, a measurement of charge symmetry breaking in np elastic scattering at 350 MeV, has completed data taking. Scattering asymmetries were measured with a polarized (unpolarized) neutron beam incident on an unpolarized (polarized) frozen spin target. Coincident scattered neutrons and recoil protons were detected by a mirror symmetric detection system in the center of mass angle range from 50°–90°. A preliminary result for the difference of the zero‐crossing angles, where analyzing powers cross zero, is Δθcm=0.48°±0.08°(stat.)±0.08°(syst.) based on fits over the angle range 55.8°≤θcm≤85.4°. The difference of the analyzing powers ΔA≡An−Ap, where the subscripts denote polarized nucleons, was deduced with dA/dθcm=−1.47×10−2 deg−1 from phase shift analyses to be [71±12(stat.)±12(syst.)]×10−4. It is expected that when all data are analyzed a statistical accuracy of about 7×10−4 in ΔA will be achieved.

This paper discusses the use of a commercially available 235U fission chamber, with a matching compensating ion chamber, originally sold as a single-ended detector with the signal conducted over the shield of a coaxial cable. The authors designed an aluminum housing that isolates the two detectors and converts the signals to full differential mode as a noise-reduction technique. The signals are processed using the switched resistor technique to extend the signal range to longer times from the peak of the pulse [Luker, S. M., Griffin, P. J., King, D. B., and Suo-Anttila, A. J., “Improved Diagnostics for Analysis of a Reactor Pulse Radiation Environment,” 13th International Symposium on Reactor Dosimetry, Akersloot, Netherlands, May 25, 2008, pp. 4–6.]. The newly configured fission chamber assembly has been used at the annular core research reactor at Sandia National Laboratories to provide a high-fidelity characterization of the neutron time profile from a pulsed operation.

We are planning to use the Tagger facility at the Saskatchewan Accelerator Laboratory (SAL) to measure the total cross section for the reaction γp → nπ+ very close to threshold. The purpose is to extract the electric dipole amplitude Eo+(π+) to high accuray. The experimental techniques involve the use of a liquid hydrogen target and the detection of the reaction neutrons in coincidence with tagged photons.