Role of Multiple Ionization in the Generation of Defects in Alkali Halides by Soft X Rays

Abstract

$F$ coloration in KCl and KBr has been studied at liquid-nitrogen temperature as a function of wavelength of monochromatic x rays on either side of the $K$ edges of Cl and Br. The coloration on the high-energy side of the edge is higher than the coloration on the low-energy side by a factor of 2.5 for KCl and 1.1 for KBr. This is interpreted as evidence for the importance of multiple ionization in the process of vacancy formation as required by a Varley-type mechanism based on an Auger effect. In KBr, the $K$-edge coloration discontinuity was studied as a function of radiation dose at 78, 195, and 300°K. At 78°K the discontinuity becomes more pronounced as irradiation proceeds and generation of new vacancies takes place. The discontinuity does not show up at 195 and 300°K, presumably because at these temperatures the coloration of existing vacancies is the dominating phenomenon.