I seem to recall from the days of my youth here in Canada that rules were
very strict concerning 'man made radioactive substances' such as Tritium
(Tritium is not found in Nature, but must be created via nuclear reactions
within nuclear reactors), but were much less so for naturally occuring
substances such as Uranium. I was attempting to obtain a supply of Radium
(much, much, much more dangerous than uranium or tritium) for a school
science experiment and discovered that at the time it was theoretically not
Also, tritium is a crucial component of various fusion reaction experiments
currently underway, and thus may be subject to special rules governing
national security in the U.S. Tritium is also very radioactive, with a
very short half life, compared to uranium 239.
On the other hand, almost every standard smoke detector contains
Californium 242(?), a man-made radioactive isotope, and I don't think that
selling smoke detectors requires a huge amount of paperwork.