I feel americium powder is far too dangerous. Just one grain in the throat, lungs or digestive tract must be bad, and fine powder flies. Beryllium powder has a (debated) bad reputation too. That's why I asked about education, training, protection.
Foils seem less dangerous than powder, but in my opinion, DON'T DO IT at all, even less with students.
Other experiments are interesting too and safe.
Play with Geiger counters to get a sense of ambient radioactivity and sources (including unbroken smoke detectors, old watches, stones...).
Operate a fusor https://en.wikipedia.org/wiki/Fusor
this produces neutrons too.
Detect cosmic rays.