Electronmicroscopic Observation of Coloured and Bleached Alkali-Halide Crystals

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Abstract
Alkali-halide crystals coloured with X-ray irradiation were observed electronmicroscopically using replica techniques. Crystals bleached by keeping them in air and by thermal treatment were also observed. Growth of crystallites was seen not only on the irradiated front face, but also on the side face and on the newly cleaved section. An interesting growth of crystallites was observed all over the front face with the progress in colouration. It was also seen on the side face that the growth of crystallites similar to that on the front face occured in accordance with the degree of colouration. At the inner part of coloured crystal, growth of crystallites was observed only along the steps or in the neighbouring part. By the process quite reverse to the crystal growth in colouration, crystallites grown during colouration disappeared in the process of bleaching. Results obtained were discussed.