E. Van Camp

A general solid angle calculation by a Monte Carlo method

Abstract A procedure is described for calculating the solid angle in a general source-to-detector geommetry, by a Monte Carlo method.

An absolute recoil-proton photoneutron spectrometer using a Monte Carlo calculated efficiency

Abstract The use of a recoil-proton spectrometer as a tool for the measurement of absolute differential photoneutron cross sections is described. The efficiency of the stilbene scintillator was calculated by means of a Monte Carlo method. The test measurements of the photoneutron spectra from 16 O and 12 C show that this simple device may prove very valuable in photonuclear research.

A Hauser-Feshbach compatible unified exciton model

Abstract The conditions under which the unified exciton model leads in its equilibrium limit to the Hauser-Feshbach model are derived and discussed. A simple extension of the exciton model is presented which exhibits the desired equilibrium behaviour. To this end, angular momentum dependent escape and spreading widths are derived. Both pre-equilibrium and equilibrium decay to specific isolated levels are discussed.

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.

Fine structure in the208Pb(γ,n) cross section

The total photoneutron cross section of208Pb was measured between 8 and 13 MeV using the bremsstrahlung photon facility from a 35 MeV linac. Considerable resonance structure was observed in the cross section, of which the peak around 9 MeV, as well as the structure around 10.8 MeV may be due toE2 excitations.

Time-evolution of isospin mixing in the unified exciton model

Abstract The unified exciton model, based on a master-equation approach, is extended to describe also the coupling between exciton states of different isospin. This allows the determination of the time evolution of the isospin mixing coefficient μ 2 ( t ). The equilibration of the excited nucleus, both in exciton number and isospin space, is discussed. It is shown that the nucleus essentially decays before full equilibrium is established.

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.