J.C. Bergstrom

Electroexcitation of the 0+ (3.562 MeV) level of 6Li and its application to the reaction 6Li(γ, π+)6He

Abstract The M1 form factor for the 0 + (3.562 MeV, T = 1) level in 6 Li has been measured in the momentum transfer range q = 0.26−1.15fm −1 . The radiative width is found to be Γ γ 0 = 8.16 ± 0.19eV by extrapolation to the photon point. Phenomenological configuration amplitudes have been obtained for the ground and 3.562 MeV level, and it is shown that the 1p harmonic oscillator radial wave functions do not give a good description of the inelastic form factor. The results have been applied to the reaction 6 Li( γ , π + ) 6 He near threshold. The theoretical cross section is 24% higher than the data. The muon capture rate in 6 Li and F A (0) are also evaluated.

Electron scattering from the 3.65 MeV (0+, T = 1) state in 6Li at high momentum transfer

Abstract The form factor ofthe 3.56MeV(0 + , T = 1) state of 6 Li has been measured for momentum transfers q = 1.0–3.0 fm −1 , and the 2.18 MeV (3 + , T = 0) and 5.37 MeV (2 + , T = 1) states have been measured up to q = 2.5 fm −1 . The 3.56 MeV form factor is analysed in terms of a phenomenological shell model with l = i valence nucleons. The radial wave functions are found to have a greater radial distribution than given by the harmonic oscillator, more closely resembling Woods-Saxon functions. The M1 form factor is found to decrease at high momentum transfer somewhat more slowly than the models predict. A technique for determining the Mλ transition current density based on the Fourier-Bessel analysis is developed and applied to the M1 transition. The M1 transition current density is obtained within a moderate error band and compared with the harmonic oscillator and Woods-Saxon densities. The M1 radiative width is 8.18 ± 0.25 eV, in agreement with previous measurements.

6Li electromagnetic form factors and phenomenological cluster models

Abstract The longitudinal form factors of the ground and 2.18 MeV (3 + , T = 0) states, and the transverse form factors of the 3.56 MeV (0 + , T = 1) and 5.37 MeV (2 + , T = 1) states of 6 Li are compared with the predictions based on fully antisymmetrized α-d and t-τ cluster models. The longitudinal form factors are adequately described by the α-d model, but the transverse form factors seem to be more consistent with a t-τ model which is close to the shell-model limit. Estimates are made for the ground state t and α spectroscopic factors. The 3.56 MeV M1 transition current density is calculated for both models and compared with experiment.

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.

Electron scattering studies of magnetic isovector transitions in 12C at high momentum transfer

Abstract The inelastic electron scattering cross sections for the M1 transition to the 15.11 MeV (1 + , T = 1) level and for the M2 transition to the 16.58 MeV (2 − , T = 1) level in 12 C have been measured in the momentum transfer region q = 0.4–3.0 fm −1 , with emphasis on precise data at high momentum transfers. Additionally, a broad state near 15.4 MeV excitation has been observed and its excitation energy and natural width have been established as 15.44 ± 0.04 MeV and 1.5 ± 0.2 MeV, respectively. The Fourier-Bessel technique for determining the Mλ transition current density has been applied to the M1 and M2 transitions. Particular attention has been paid to the Coulomb corrections required to deduce the PWBA form factors. The M1 radiative width is Γ γ 0 = 38.5 ± 0.8 eV.

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.