Radioactivity in Blue Topaz

A lot of minerals have detectable radioactivity due to natural concentrations of uranium, thorium, or potassium, but the radioactivity in blue topaz has a unique explanation: virtually all of the blue topaz sold in jewelry is technogenic, produced by irradiation of clear topaz in accelerator and nuclear reactor facilities. The darker and more saturated blue colors require fast neutron irradiation, and in addition to creating the displacement damage needed to induce coloration, these neutrons induce radioactivity in the stone through (n,g), (n,p), and fission reactions with trace constituents. In this video we use gamma spectroscopy to look at the radiation from samples of "London blue" topaz faceting rough from Thailand, India, and Brazil (although, admittedly, the country of origin may say little about where the clear topaz feedstock originated or where the reactor processing was undertaken). The results include interesting induced gamma activities including europium-152, europium-154, tantalum-182, scandium-46, cobalt-60, manganese-54, cesium-134, and cesium-137 (which is a fission product, and suggests small amounts of natural uranium or thorium in the topaz). Give your loved one the gift of modern nuclear science in wearable form this holiday season!