Energetic-distribution measurements of the atomic-field pair production process at low energy by using a streamer chamber

Abstract

The differential cross-section dσ/dE+ for the atomic-field pair production in uranium (Z=92) and barium (Z=56) targets is studied. The incident-photon energy isk=2.62 MeV. The results concern the upper half-part (0.5<Y=(E+−1)/(k−2)<1.0) of the e+ energetic spectrum. The comparison with the theoretical results of Overbo, Mork, Olsen confirms the Coulomb correction values and the asymmetrical shape of the e+ spectrum provided for in calculations, but the measurements are not accurate enough for a comparison with the screened theory of Tseng, Pratt. From the experimental point of view, the pair events are registered in a streamer chamber; insulating UO2 and BaF2 targets are located inside, a monitoring target gives the electronical dead-time correction. A further experiment is performed with a low-Z target (Z≃5, Coulomb correction negligible) to make up the electronical and kinematical detection coefficients. About 8000 pair events have been registered on the whole; 3200 measured in the experimental targets.