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 cps background, was 12 cps.
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 that stands out is the peak at ~31 kev. I have not been able to identify it. You would expect to find Cesium-137 when you see X-ray peaks this high, at this energy. There is no indication in the chart that it is.
One possibility is that there is some naturally occurring Cesium mineral present, and with the high beta radiation level, is creating Bremsstrahlung radiation from the Cesium. This is just a guess.
Does anyone here have any alternative suggestions for the source of the ~31keV peak?
