A. De Graeve

180° Compton scattering by the proton below the pion threshold

Abstract Absolute cross sections for Compton scattering from protons have been determined at 180° for the backscattered photon at incident laboratory photon energies of 98 and 132 MeV. For the difference between the electric and the magnetic polarizability of the proton a value of (7.03 − 2.37 +2.49 − 2.05 +2.14 ) × 10 −4 fm 3 has been derived using the predictions from calculations based on relativistic dispersion relations.

The forward, backward and 90° deuteron photodisintegration between 7 and 19 MeV photon energy

Abstract The 0° and 180°, as well as the 90° differential cross sections for the 2 H(γ, p)n reaction have been measured at lab photon energies between 7 and 19 MeV. Special attention was paid to the accuracy, in particular by measuring the forward Compton electron yield. For the extreme angles, the statistical error on our results amounts to 4–5% (0°) and 7–8% (180°), respectively, while the systematic uncertainty is at most 3%. The data confirm the existence of a minimum in the forward cross section and indicate beyond any doubt that the fore/aft ratio is larger than unity. Comparison shows reasonable agreement with the results from recent “conventional” theoretical approaches, including meson exchange and relativistic corrections, although the description of the c -coefficient, appearing in the Partovi expansion of the differential cross section, remains unsatisfactory. A possible source for this discrepancy could be the inadequate description of the El and/or the E2 transition operator.

The photodisintegration of the deuteron below the pion threshold at 180° for the outgoing proton

Abstract Absolute differential cross sections for the photodisintegration of the deuteron at 180° for the outgoing proton have been determined at photon laboratory energies between 30 and 100 MeV. The statistical uncertainty on the individual data points is about ±4%, while the overall systematical error amounts to ±3%. The new CM frame 180° cross sections do not seem to exhibit a minimum and are in good overall agreement with the predictions from modern calculations. Between 65 and 100 MeV the mean fore-aft ratio of 1.499±0.032 was obtained in excellent agreement with modern theoretical estimates.

Search for the minimum in the forward2H(γ,p)n cross section

The forward2H(γ,p)n cross section was measured at 7.2 and 8.5 MeV photon energy. The new absolute values confirm the theoretically predicted presence of a minimum in this cross section. A discrimination is made between the results from various theoretical descriptions.

Forward photodisintegration of the deuteron between 20 and 100 MeV photon energy

Abstract Absolute differential cross sections for the forward deuteron disintegration have been determined at photon laboratory energies between 20 and 100 MeV. The statistical uncertainty on the individual results is about ±2.5%, while the overall systematical error amounts to 3%; the angular resolution equals 1.5°. The new CM-frame cross sections are in fair agreement with the predictions from recent theoretical calculations.

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.

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.