P. Van Otten

The absolute forward photodisintegration cross section of the deuteron at low excitation energies

Abstract The 2 H(γ, p)n cross section was measured absolutely at 0° for the outgoing proton, for photon energies between 8 and 18 MeV. The rising trend observed in the cross section in this energy region indicates the existence of the theoretically predicted minimum. Our results at E γ ≈10 MeV are well described by recent relativistic calculations, the data around 15 MeV, on the contrary, are commonly underestimated.

Isospin mixing during the decay of the giant dipole resonance: A case-study in 28Si

Abstract The magnitude of the isospin mixing in the initial 1p-1h doorway state and in the underlying compound states of the 28 Si giant dipole resonance is estimated from (γ, p), (γ, α) and (γ, n) cross sections. From the mixing coefficients, mixing widths of about 40 keV and 25 keV are deduced for the 1p-1h state and for the compound states respectively. This seems to indicate that the isospin mixing widths are roughly independent of the complexity and lifetime of the state involved.

A general Monte Carlo calculation for the geometrical efficiency of a detection system

A general Monte Carlo procedure is described for calculating the geometrical efficiency of a detection system with regard to a beam of particles impinging on a gaseous target or on a plane parallel target plate with finite thickness, while the detected particles are emitted with an isotropic angular distribution or one of the form [1−0.5P2 (cos θ)], with P2 (cos θ) the second Legendre polynomial. This method was successfully applied to the analysis of the 16O(γ, P0)15N data.

Charged-particle decay of 28Si induced by quasi-monochromatic annihilation photons in the GDR

Abstract Spectra of protons and alpha-particles, emitted from the giant electric dipole resonance of 28 Si excited by quasi-monochromatic photons from in-flight annihilation of accelerated positrons, were measured. Cross sections for six charged-particle decay channels were extracted in the energy region from 16.8 to 25.7 MeV. While the ( γ , α 0 ) cross section is completely statistical in nature, the (γ, p) process was found to have a 65% semidirect component, mainly in the ( γ , p 0 ) and ( γ , p 1+2 ) channels.

The positron production and acceleration facility at the 90 MeV electron linac of Ghent State University

The electron-to-positron conversion and acceleration system is described. It essentially consists of a 3 mm thick W-Re converter target immersed in a magnetic lens and placed in between both sections of a linear electron accelerator; it further comprises a long solenoid over the second linac section and a short coil to bridge the gap between the converter and the accelerator section. Mean positron currents (within Δ EE = ± 1%) of more than 1 nA at positron energies around 25 MeV are readily available, while this value may be enhanced to about 4 nA. The practical possibilities of this facility are illustrated by the measurement of the 28Si photoproton spectrum using a quasimonoenergetic photon flux produced by the in-flight annihilation of the accelerated positron beam.

Isospin Mixing During the Decay of the Giant Dipole Resonance

Isospin mixing is studied in the decay of the28 Si Giant Dipole Resonance. Mean isospin mixing coefficients are deduced for the 1p-1h doorway states and for compound states. A simple model for the equilibration of the T> GDR is presented, which accounts fairly well for the observed isospin mixing.

An intermediate energy photoproton spectrometer using a quadrupole triplet magnet

Abstract A new photoproton detection system for use in intermediate energy (30–90 MeV) photonuclear reactions is presented. It consists of a quadrupole triplet magnet which focusses the protons on a hyperpure germanium detector, situated 2–3 m away from the reaction target. The transmission function (solid angle vs relative momentum) is calculated using a Monte Carlo method, the result of which is in excellent agreement with the experiment. An example of a photoproton spectrum measured with the new set-up is also given.