Re: the topaz, the older stuff was much more irradiated than the newer stuff is. Hummingbirdstones is right; the geiger is the best way to see if they're really hot.
Debbie K
I did a lot of research on this when the topic came up at GemologyOnline a few years ago. When treated blue topaz first came to market in the 1980s a few "hot" batches were discovered. The stuff was initially irradiated by dental X-ray machines in Brazil but the dangerous London Blue stones were treated in nuclear reactors and took a fairly long time to become inert.
I forget all the details but since then strict controls on topaz imports have been established in the U.S. See this report from the Nuclear Regulatory Commission:
https://public-blog.nrc-gateway.gov/2014/12/08/blue-topaz-the-irradiated-gemstone/ I've dealt in the material for 30+ years and have never heard of a single case of anyone being sickened by handling or wearing it. In the case of London Blue it's required to be stored for specific cool-off periods before it can be shipped to the U.S. These regulations are strictly enforced by the NRC.
Re: Geiger counters, a funny story. Eight or ten years ago an Indian dealer sent me large chrysoberyl cat's-eye and asked if I could sell it for him. It was a yellowish stone, not the brandy color that's considered most desirable in the Trade, but it was huge, nearly 20 carats, and of fine quality. It so happened that about the same time a few of the yellowish Indian stones had been sent to an Indonesian company which irradiated them to darken the color. They were sizzling "hot" when they came to market and this set off a big alarm among people who dealt in those goods.
Not knowing that, I took the stone to several major gem dealers of my acquaintance in L.A. When I pulled the stone out of my pocket, people's faces blanched and one guy ran quickly to a back room and came back lugging a Geiger counter. He gingerly tested the stone and got nothing but a normal background radiation count. But I had trouble convincing other dealers the stone was safe. As it turned out, very few of the dangerous irradiated stones were ever discovered but it set off a panic that I still hear about all these years later.