Abstract
Low temperature thermal conductivity techniques have been used to monitor the concentration of Cr2+ in ruby. Cr2+ was produced in the ruby by gamma -irradiation at 77K and was removed (bleached) progressively by exposure to UV radiation whilst the specimen was at 77K. This bleaching treatment was carried out using three different wavelengths of electromagnetic radiation-334, 365, and 435.8 nm. Two bleaching processes were identified: one initial, rapidly saturating process and one clearly UV dependent process. The latter process has an activation energy between 2.85 and 3.4 eV and induces an exponential fall in Cr2+ concentration-the relaxation time being approximately 230 hrs.
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