Abstract
Detailed measurements have been made on the conversion of U1‐α centre pairs into U2‐F centre pairs in KBr: KH crystals extending the results and suggestions made earlier by Delbecq et al. It is shown that part of the thermally most stable vacancy—interstitial pairs undergo further conversion upon U1 bleaching. Furthermore at 4.5 °K a complete reverse reaction can be induced by bleaching with F light. From these quantitative results the oscillator strength of the U2 band can be determined. A refinement of Delbecq's conversion model is proposed.