H.S. Caplan

The photon tagging facility at the Saskatchewan Accelerator Laboratory

Abstract A photon tagging facility has been constructed for use with the c.w. electron beam at the Saskatchewan Accelerator Laboratory (SAL). The facility consists of a “clam-shell” type magnetic spectrometer with a 62 channel plastic scintillator focal plane detector allowing a post-bremsstrahlung electron energy resolution of 1%. Specialized focal plane and coincidence electronics have been designed and constructed at SAL and allows experiments to be performed with average tagged photon rates of greater than 1 × 108/s.

Inelastic electron scattering from 10B

Abstract Electron scattering form factors were measured for six transitions in 10B in the momentum transfer range 0.61 to 1.81 fm−1. Ground state radiative widths were extracted by means of the generalized Helm model for the levels at 1.74 MeV (M3), 5.17 MeV (M1 + M3), 6.03 MeV (C2 + C4), 7.48 MeV (M1), 8.07 MeV (C2) and 8.9 MeV (M1 + M3 or M2). The transverse form factors for the 1.74 and 5.17 MeV levels agree well with predictions based on Cohen-Kurath wave functions. The longitudinal form factor for the 6.03 MeV state shows effects due to the deformation of 10B and is in good agreement with the deformed Hartree-Fock shell model prediction of Bouten and Bouten. Estimates are presented for the ratios of radiative pion capture rates leading to analogue states in 10Be.

An overlapping multichannel detector system

Abstract A multichannel system for the detection of medium-energy electrons is described. The system consists of 24 overlapping plastic scintillators which define 45 momentum channels. Fast-logic circuitry is used to process the signals and the data is read into an on-line computer via a buffer memory. The performance is characterized by a high count-rate handling ability, good background rejection and moderate resolution.

Electron scattering from 70Ge and 72Ge

Abstract Cross sections have been measured for the elastic and inelastic scattering of electrons from 70 Ge and 72 Ge for momentum transfers from 0.65 to 1.14 fm −1 . Values for the parameters of a Fermi type ground-state charge distribution were obtained from a phase shift analysis of the elastic cross sections. The rms charge radius corresponding to these parameters is 4.07±0.02 fm for 70 Ge and 4.05±0.03 fm for 72 Ge. Using DWBA analysis the reduced transition probabilities for the electroexcitation of the 2 1 + and 3 1 − states were found to be: B (E2, ω )↑ = 19.7±1.2, 26.8±2.0 W.u.; B (E3, ω )↑ = 36±5, 37±7 W.u. for 70 Ge and 72 Ge respectively. The J π = 3 − assignments for the state at 2.562 MeV in 70 Ge and 2.515 MeV in 72 Ge are confirmed.

Electron scattering from 17O

Abstract Cross sections for elastic and inelastic scattering of electrons from 17O have been measured for momentum transfers up to 1.2 fm−1. The elastic cross section indicates that the rms charge radii of 17O and 16O are equal to within a few parts in a thousand: 〈r 2 17 〉 1 2 〈r 2 16 〉 1 2 = 1.0015 ± 0.0025 . Reduced transition probabilities and ground-state radiative widths are deduced for 17O excited states below 9 MeV. Various aspects of the inelastic spectrum are discussed, with emphasis on the “single-panicle” levels at 0.871 ( 1 2 + ) and 5.083 ( 3 2 + ) MeV, the levels at 7.569 ( 7 2 − ) and 7.378 ( 5 2 + ) MeV, and the spectrum of electric octupole excitations.

Electroexcitation of 16O levels near 10 MeV excitation

Abstract The electromagnetic form factors of the 2 + (9.85 MeV) and 4 + (10.34 MeV) states in 16 O have been measured for momentum transfers between 0.7 and 1.2 fm −1 . The results for the 4 + state are compared with the predictions of the three-component Brown-Green model. The present data and those of a previous electron scattering experiment are interpreted in the framework of a two-component model in order to obtain rough estimates of the β 2 and β 4 deformation parameters. Predictions for the 2 + (9.85 MeV) level form factor, within the context of an axially asymmetric rotor model, are compared with the experimental form factor. It is found that this model gives a poor description of the data. Radiative widths and transition radii have been determined by a Helm model analysis.

Response of a BaF2 detector to photons from 75 to 200 MeV

Abstract A large cylindrical BaF2, crystal 22.9 cm long and 12.7 cm in diameter, was calibrated with monochromatic photons from the tagged-photon facility at the Saskatchewan Accelerator Laboratory. The measured spectra for the energy deposited in the crystal from the resulting electromagnetic shower compares very well with predictions of the Monte Carlo shower simulation code EGS4. A method for establishing a transferable energy calibration using cosmic ray muons is also presented.

Nuclear compton scattering from pion threshold to the delta

Abstract The first measurements of elastic photon scattering on complex nuclei from 150 MeV to the Δ(1232) (Eγ = 300 MeV) are compared with theoretical calculations. Data on 4He at the Δ peak are in agreement with a Δh calculation, but substantial disagreement occurs at lower energies that is at least partly due to the approximate treatment of non-resonant parts of the elementary nucleon amplitude. An impulse approximation calculation which includes meson exchange provides an adequate description of the data at 187 MeV on 4He. Improved data on the proton at 20–30° and 120–140° at a range of energies are in agreement with a recent dispersion relation calculation. Data taken on 12C are still too preliminary to report, due to the difficulty of eliminating inelastic contributions.

Sore - A Pulse Stretcher for the Saskatchewan 300-MeV Linac

A design study has been made of a pulse stretcher to increase the duty factor of the 300 MeV electron accelerator of the Saskatchewan Accelerator Laboratory. The design was constrained by the desire to house the pulse stretcher within the existing accelerator building and to make maximal use of existing beam transport lines. The pulse stretcher ring consists of two 180/sup 0/ bend regions connected by achromatic straight sections. The overall length is 50.49 m and the width is 6.64m. The modes of injection and extraction will be available. In the first mode a shortened linac pulse of 300 ns duration will be injected during a single turn directly into the closed orbit of the pulse stretcher. A second mode of injection/extraction involves use of a longer linac pulse. The basic geometry of the PSR is dictated by the dimensions of the accelerator vault and access room.

Low-lying octupole excitations in 17O

Abstract Inelastic electron scattering experiments were performed on a 17 O gas target in a range of momentum transfer q = 0.6−1.1fm −1 ; B (E3) values for twelve odd-parity levels were obtained from the measured Coulomb form factors. The results are discussed in terms of the weak coupling model.