17th September 2017
A concerned person sent me this small sample of Cerium optical polish to test with my scintillator equipment. They detected high cpm when they tested a small amount with their Geiger counter.
Cerium Dioxide is a rare earth, used widely for glass and lens polishing. It is supplied in different colours. Tan to dark brown are the most common colours. These colours indicate the presence of iron. Cerium Dioxide that is pure white in colour, is a lot more expensive to buy.
Reportedly, in the USA, a large optical manufacturer had all their cerium polish, plus a semitrailer load of ground glass, grinding, and polish sludge, impounded by the EPA, because it was found to be very radioactive.
By itself, pure Cerium oxide dry dust inhalation can be a health hazard, let alone adding radioactive contamination to the mix.
I also tested this sample with a sensitive Pancake Geiger counter. It was only a Beta and Gamma test, as I left it in the zip lock bag it was sent to me in. This small sample measured ~235 cpm above background level. Gamma testing, using a 2" scintillator probe, minus the test chamber 8 cpm background, was 12 cpm.
Reports indicate that samples of dark brown Cerium Dioxide may sometimes be contaminated with Thorium, which this sample test here, shows to be the case. As well as the Pb-212 peak, (the decay daughter of Thorium-232), peak positions suggest that some Pb-214 may also be present. The peak around 35 keV is most likely is most likely from the X-ray fluorescence of Cerium (35 keV). The X-ray 35 keV fluorescence peak is created by the beta radiation bombardment of the Cerium in the sample.
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