Interaction betweenFcenters and interstital H atoms in KCI crystals

The radiation damage of KCI single crystals containing $U$ centers (substitutional ${\mathrm{H}}^{-}$ or ${\mathrm{D}}^{-}$ ions) is found to be dependent on the temperature and on the spectral purity of the uv radiation used. The interaction between $F$ centers and $U_2$ centers (interstitial ${\mathrm{H}}^0$ or ${\mathrm{D}}^0$ atoms), products of the radiation damage, gives rise to new optical transitions on the visible part of the spectra. The isotope dependences of the wavelength bandwidths of the new absorption bands are studied. Experiments on the radiation damage by uv and by x rays on${\mathrm{H}}^{-}$ ${\mathrm{H}}^{-}$ aligned pairs are also discussed.