Egyptian research reactor and by γ rays from a gamma source. Changes in the color of the stones are observed which can be attributed to the formation of defects in the structure of the stones. The defects can absorb certain wave length which is observed as a change in the stone color. The absorption of light is investigated by an optical spectrophotometer technique at different irradiation and heating conditions. Raman studies of topaz stones showed a relation between the color changes with changes in the intensities of the band ...