X‐Ray production and thermal annealing of frenkel pairs in KCl

The X‐ray production and thermal annealing α‐centres (isolated negative ion vacancies) are studied in KCl as a function of purity and the temperature of irradiation. At any temperature the α‐centre production results from competition between the formation process and thermally activated destruction of negative ion vacancies. Since the latter process is strongly temperature and structure dependent, the α‐centre production is structure sensitive or insensitive depending on the temperature of irradiation. From the point of view of thermal stability the α‐centres produced by X‐rays can be divided into two groups. The first group includes α‐centres which decay below 77 °K and whose thermal stability does not depend on the purity of the sample. The second group includes α‐centres which decay in the 100 to 250 °K temperature range and whose thermal stability is strongly structure sensitive. Finally, some results on the influence of electron traps on α‐centre formation are reported.