Processes of importance in the coloration of solids by x-radiation are discussed on the basis of Seitz's hypothesis that vacancies are created at jogs on dislocations or at other imperfections. The interaction between $F$ centers and dislocations is calculated, and it is shown that $F$ centers located within about 50A of edge-type dislocations would experience measurable broadening and perhaps shifting of their absorption peaks, in contradiction of experiment. From the available energy in the form of point thermal pulses, it is shown that most vacancies freed from jogs or other sources probably make less than a thousand atomic jumps during x-irradiation at He temperatures and hence are unable to diffuse more than about 100A from their sources.

The tunneling of $F$-center electrons to positive-hole centers is calculated, and it is concluded that tunneling can occur with high probability over a distance of ∼30A by an electron in its ground state, ∼40A in its first excited state. Such tunneling is important in limiting local $F$- and $V$-center concentrations even at He temperature in the dark. Crystals achieving macroscopic concentrations of the order ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$, it is concluded, must contain very high densities of vacancy sources to be consistent with the requirements of both the large tunneling range and the small diffusion distance.

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