Compton scattering in a large-aperture positron imaging system

Compton scattering of gamma rays within the image volume has been assessed for a large-aperture positron-emission-tomography imaging system. The Compton scattered attenuation and the Compton scattered background were both modeled and measured for point sources centered in scattering spheres up to 10 cm in diameter. Good agreement was obtained between simulations and measurements. The attenuation problem is independent of the detector system, but its correction is more difficult in a large-aperture system. The scattered coincidence background is large in this system (43% for a 10-cm-diameter scattering sphere), but the background overlap is reduced with 3D imaging.     

Proton-proton correlations at small relative momentum in neon-nucleus collisions at E/A=400 and 800 MeV

Proton-proton small angle correlations have been measured in neon-nucleus collisions, using the 4 pi detector Diogene, at 400 and 800 MeV per nucleon incident energies. Values of the size of the emitting region are obtained by comparison with the Koonin formula, taking into account the biases of the apparatus. The dependence of the density on target mass and incident energy is also analysed.