Double positron-electron pair production by 6.6-MeV gamma rays

Abstract

Double positron-electron pair production by 6.6-MeV $\ensuremath{\gamma}$ rays was investigated via measurement of fourfold coincidence rates of annihilation quanta in targets of beryllium, boron, carbon, aluminum, sulphur, copper filings, and solid copper. Following an accounting for the interfering bremsstrahlung-cascade and direct-cascade effects a measure of the cross section for the process, relative to that for single-pair production, was obtained as $\frac{{\ensuremath{\sigma}}_{\ensuremath{\pi}\ensuremath{\pi}}}{{\ensuremath{\sigma}}_{\ensuremath{\pi}}}=(1.82\ifmmode\pm\else\textpm\fi{}0.58)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$.NUCLEAR REACTIONS Measured $\ensuremath{\sigma}$ for double-pair production at 6.6 MeV.