Feature Gems & Gemology, Winter 2011, Volume 47, No. 4

The Radioactive Decay Pattern of Blue Topaz Treated by Neutron Irradiation

A systematic study of 15 neutron-irradiated blue topaz samples was conducted using high-purity germanium (HPGe) digital gamma-ray spectroscopy. The specific activity of the detected radionuclides (134Cs, 182Ta, 46Sc, and/or 160Tb) was measured, and the decay pattern of the irradiated topaz was determined. Based on the time elapsed since their removal from the nuclear reactor, the amount of time required for the residual radioactivity to decay to safe levels was calculated. Most of the samples were safe at the time of the first measurement (95 days after irradiation), but higher concentrations of radionuclide impurities in some samples will require them to be quarantined for several years.