Nuclear forensics of a colored gemstone: evidence of proton bombardment of a blue topaz

A blue topaz was investigated radiologically for forensic purposes. It clearly exhibited detectable activities of 22Na (0.28±0.01 Bq). The occurrence of this artificial radionuclide evidences fraudulent irradiation of the gemstone with protons to give it its blue color. It can be assumed that also 7Be must have been produced in the course of proton bombardment, yielding even greater activities than 22Na. Since no traces of short-lived 7Be could be detected, the topaz must have been irradiated at least 300 days prior to measurement.

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► A blue topaz was radiologically investigated for forensic purposes.
► Detectable activities of 22Na were found.
► The lack of 7Be indicates that the gemstone was irradiated >300 d prior to measurement.
► The irradiation was performed by fraudulent intent to give the topaz the blue color.