"Old thorium nitrate crystals are packed with radon-228, radon-224 and radon-220, and if the bottle has been sealed for decades, there's a high radon
buildup inside"
No, not really.
After a while (decades) thorium would be in equilibrium with radon. There's only 1 isotope of radon produced by thorium. It (220) has a half life of
about a minute. The ratio of the numbers of atoms of Thorium to Radon is the same as the ratio of their half lives (about 1 in 10^18).
And that would decay away in ten minutes if you opened the bottle to let it out. (of course, most of it would never get out of the crystal lattice-
diffusion would be slower than decay.)
Old samples are more radioactive then fresh ones. But in the case of thorium it's about a dozen times more active. Also, remember that any rock with
thorium in is automatically "old".
So, overall you have something roughly as radioactive as the Th (and decay products) in 16 tonnes of dirt.
I still think customs will object to it. |