Research On Gemological Characteristics And Radioactivity Of Blue Topaz

This paper selects the irradiated-blue topaz as the main research object, comparing with the ones treated by diffusion, coating and natural ones. According to a series experiments,the auther did a futher research on the gemological characteristics by the cathodoluminescence, differential thermal analysis, chemical composition analysis and spectrum analysis,and slso explored radioactive residue of irradiated topaz and the quantitative characterization of the commercial color words"London blue", "Swiss blue" and "sky blue".According to the study, all the testing irradiated blue topaz is mainly F type, the main component is alumina and silica, the content of fluorine is close to theory values. Trace fluorine escaping during the irradiation process may result in the slightly lower content of fluorine than that of natural topaz, and the total content of trace elements is basically lower than 1%, especially the content of La, PR, Nd, Gd, GE and Ti is higher than that of natural topaz.The gemological character was similar between irradiated-topaz and natural topaz. The refractive index is 1.610-1.627,and the relative density is 3.51-3.57.The irradiated-topaz under UV-fluorescence properties in long wavelength was light green,but under cathodoluminescence it was blue,and was a bit weaker than the natural ones.The coated-topaz has different colors in pavilion and crown department.Both coated and diffusion blue topaz were pale pink under the color filter.Based on the analysis of differential thermal testing, it is obvious that the exothermic reaction of topaz is caused by internal hole defects gradually disappeared following the increasing temperature, then blue topaz fade at a high rate of speed between 350℃ and 600℃.However, the weight lose is 3.5～6.1% in the whole reaction process, that is to say,there is not any nature changes except for the color.The Ultraviolet visible absorption of irradiation and natural blue topaz is at 610nm obviously, the deeper the color is, the higher the absorption intensity is, there is a weak absorption at 430 nm of the London blue topaz. All the infrared spectrum of topaz is similar, such as the strongest absorption peak of hydroxyl groups among 4802-4423 cm-1 and 3964-3352cm-1 is caused by the fundamental stretching vibration, combination bands and frequency doubling vibration.The Raman spectra of irradiated blue topaz don’t have the Al-0 bending vibration and the Si-O symmetric stretching vibration at 925cm-1 and Si-O bending vibration at 519cm-1 move to the lower wavelength.The electron spin resonance confirmed the presence of color centers.According to the low background gamma instrument test, it is obvious that the residual radioactivity of irradiation London blue topaz is higher than that of Swiss Blue, total activity were lower than the exemption value 70Bq/g, above all, the radioactive of radiat-ion blue sky and natural blue color is under the detection limit.Through the color quantitative characterization of topaz, the color saturation effects more on the value of topaz.