Measurement of vacuum-assisted photoionization at 1 GeV for Au and Ag targets.
We report a measurement of photon impact ionization of K and L shell of Au and K shell of Ag targets in the 1-GeV energy range. We show that the cross section is dominated by a contribution from a new channel called vacuum-assisted photoionization. In this process the energy-momentum balance associated with the removal of the innershell electron is obtained by conversion of a high-energy photon into an electron-positron pair. This measurement is consistent with the theoretical prediction that vacuum-assisted photoionization is the most probable ionization mechanism at very high energies.
Institut de Physique Nucléaire, CNRS/IN2P3, Université Claude Bernard, Lyon I, 4 rue E. Fermi, F-69622 Villeurbanne cedex, France.
D
D
Dauvergne
A
A
Belkacem
F
F
Barrué
J P
JP
Bocquet
M
M
Chevallier
B
B
Feinberg
R
R
Kirsch
J C
JC
Poizat
C
C
Ray
D
D
Rebreyend