Radon from Thorium? I don't think so…
Deseret News: ‘No thanks’ to uranium waste plans
One of the fears about the waste from FMRI Inc. is over thorium, found naturally in the earth’s crust and contained in the waste from Oklahoma. As thorium decays, it produces the radioactive gas radon. The concern about radon is that it could cause lung cancer in humans.
The radon isotope produced in the decay of thorium-232 is radon-220. It has a half-life of 55 seconds. Which means that in 1-2 minutes this gas has to leave the ore it came from, drift into your lungs, and decay into polonium-216. Possible? Perhaps if you’re snorting thorium ore. Likely? Not even remotely.
Uranium-238, on the other hand, produces radon-222, which has a half-life of 3.82 days, which lasts about 6000 times longer than the radon produced by thorium. So where do you think the radon comes from?
Check out thorium and uranium decay chains on the Radioactive Decay Applet.