Thank you for the comment. However, inside this poisons cabinet, there is no compartment to segregate the thorium and uranyl nitrates, not even a glass partition.
If they are in glass bottles, you won't need additional glass partition.
These nitrates are are put side by side with mercury, arsenic, and cyanide compounds. Is it logical to assume that in the absence of segregation, the latter compounds inside the cabinet are contaminated?
Contaminated? As long as you treat your chemicals seriously, you should not contaminate one with another, although during normal usage some traces can be transferred between bottles, as a dust for example. That's unavoidable, unless you follow very tight procedures (which would be nonsensical in this case).
To some extent if other substances are irradiated with alpha particles from the U and Th compounds, they can have some traces of induced radiation (not sure what is the correct English term). But we are talking about radiation levels orders of magnitude lower than the original samples.
I wonder which of these two was responsible for the effect Hunter reported.
Please remember it is not radiation presence that is dangerous, it is the amount of radiation that is important. Just because we can measure the sample as being more active than the background doesn't mean much. Compare
http://xkcd.com/radiation/