K-shell ionization and double-ionization of Au atoms with 1.33 MeV photons

摘要

At relativistic energies, the cross section for the atomic photoelectric effectdrops off as does the cross section for liberating any bound electron through Compton scattering. However, when the photon energy exceeds twice the rest mass of the electron, ionization may proceed via electron-positron pair creation. We used 1.33 MeV photons impinging on Au thin foils to study double K-shell ionization and vacuum-assisted photoionization. The preliminary results yield a ratio of vacuum-assisted photoionization and pair creation of 2x10(sup -3), a value that is substantially higher than the ratio of photo double ionization to single photoionization that is found to be 0.5-1x10(sup -4). Because of the difficulties and large error bars associated with the small cross sections additional measurements are needed to minimize systematic errors.