Related rare earth such as lanthanum are often produced from the same sources, with monazite being up to 25% lanthanum.
This decay process means these thoriated glass lenses can gradually become more radioactive over time, as the more highly radioactive decay products build up in the glass. You would expect the radioactivity to decrease over time.
Thorium is radioactive itself, emitting alpha particles.
The resulting "daughter" products of that radioactive decay series also produce both alpha and beta particles.
An amateur treasure hunter in Germany has stumbled upon what could be radioactive material from a secret research facility dating back to World War II.
64-year-old Bernd Thälmann was exploring the ground in Oranienburg, north-east Germany, with his metal detector when it gave an unusual ‘bleep’.
This was restored from a copy I made in November 2003; Bob may have added to or edited this page after that. Industar 61 lens (lanthanum glass) Lens Faults Pages Photo. Maybe some of those bargains you got on EBAY are "hot" in a different sense than you might have thought!
“A cloud shaped like a mushroom with turbulent, billowing sections (at about 7000 metres) stood, without any seeming connections over the spot where the explosion took place.
But after chemically purifying the thorium from its ore sources, the thorium is relatively free of these daughter products.
Over time, the thorium decays, and the levels of radioactive daughter by-products builds up.
Strong electrical disturbances and the impossibility to continue radio communication as by lighting turned up.” There are claims that his testimony was corroborated by another pilot, while an Italian correspondent also saw the explosion, reporting the incident to Italian Fascist leader Benito Mussolini.
According to Berlin historian Rainer Karlsch in his book , German scientists carried out three nuclear weapons tests just before the end of the Second World War.