Production and decay of the F– centre in KCl studied by pulse radiolysis

Abstract

The thermal decay of F^– centres has been studied by pulse radiolysis in pure KCl crystals. At room temperature ∼75% of the F^– centres decay exponentially with a mean life of 190 µs. The other 25 % decay by a non-first order process (perhaps by reaction with unstable hole centres).

As the temperature is lowered, the fraction of non-first order process becomes smaller, and is zero below 270 K. The rate constant for the first order process decreased with temperature; the activation energy was 0.60 ± 0.04 eV.

The lifetime of 190 µs was found to be independent fo both the integrated total dose given to the crystal and the dose per pulse. This implies that the F^– decay does not involve reaction with any other radiation-produced species, either short- or long-lived. A new mechanism for F^– decay is put forward, involving thermal ionisation as the initial step, followed by F₂ centre formation.