New data for total He3(γ,p)D and He3(γ,pp)n cross sections compared to current theory

Abstract

A simultaneous measurement of the cross sections of the He3(γ,p)D and He3(γ,pp)n reactions has been performed for the first time using monoenergetic pulsed γ-rays at Eγ =10.2 and 16.0 MeV. Charged fragments from the reactions were detected with an efficiency of 100% using a 4π time projection chamber containing He3 gas as an active target. The incident γ-ray flux was measured by a γ-ray detector. Both the track and energy loss signals of charged fragments were obtained in an off-line analysis and used to clearly identify the reaction channel. Thus, the (γ,p) and (γ,pp) cross sections have been determined with small uncertainty. A comparison of the new data to current theory based on the AV18+Urbana IX nuclear forces including π- and ρ-like meson exchange currents shows a severe discrepancy at 10.2 MeV, while at 16.0 MeV data and theory agree within about 12%. Three-nucleon force effects are small, but in general shift the theory in the correct direction. © 2006 The American Physical Society.