F-center formation by Br K-hole Auger decay in KBr

Spectral dependence of the F-center formation efficiency has been measured for KBr single crystals at liquid-helium and nitrogen temperatures in the vicinity of the K edge of bromine at 13.47 keV. The F-center formation efficiency was evaluated by the optical absorption measurement under irradiation with monochromatized synchrotron x rays. The efficiency was normalized to the deposited x-ray energy estimated by a sensitive photocalorimetric measurement. It has been found that the F-center formation efficiency shows an ∼24% stepwise increase above the core threshold at liquid-helium temperature. This result suggests that the multiple ionization mechanism, following the core-hole Auger cascade, might participate actively in the F-center formation process.