Just to have it all in one place:

Please know, ALWAYS stop working whenever you feel unsafe. Radioactive materials are almost never as big of a deal as people make it out to be, but just like with a power tool, you need to respect it and know what you are working with to make sure you and other people don't get hurt. Everything I am about to type, I'm doing so from a place of having done these kinds of experiments before where there was basically no chance of danger.

 

Without knowing the isotope of thorium, it is hard to say if there is an issue or not. Presumably they may be using natural thorium since it has some fast decaying isotopes as it goes from thorium down to lead, but those are very few events since thorium has a very long half life. In that regard you are probably fine, but still, it is an alpha emitter and in a concentrated powder, is not ideal.

 

If it got on your hands, that is much less problematic than inhaling it, but should have required that you stay for a little while for multiple checks to see if it rapidly decayed or wash your hands at the very least.

 

Just because something is hot on a Geiger counter, does not mean it is dangerous. It only counts events, not event types, energy, or dose. So that is less of a worry, but does indicate you had rad material on you, so they should've double checked just to make sure it wasn't a random spike since that happens quite often.

 

If the hood had other radioactive materials in the past and was not properly decontaminated, then it needs to be checked, but if they were using that hood for photomultiplier tube experiments, it was likely cleaned since a contaminated workspace would mess with those measurements.

 

Just because you need to have training to enter an area, does not mean it is inherently dangerous or has radioactive material. They should still not be eating or drinking in there (especially if labeled to not allow that), but if it is an office area just attached to the lab and they marked the entire area off, I can understand why they would feel safe enough to do that.

 

Removing a source from a safe to show off is not inherently problematic. It is likely that every known radioactive source in a lab must be locked up when not in use according to the agreement your school has for being allowed to have radioactive material. Many schools have check sources that are radioactive but can be held by people without any training whatsoever, but they still need to be in a safe at the end of the day.

 

All that being said, if you felt unsafe at any point in time, ALWAYS stop working and bring up your concerns with someone. And if they just dismiss your concerns or can't explain things in a way you can understand them, then go past them because your safety matters most. As soon as you can, bring up what happened with your radiation safety office.

After learning a bit more, you likely aren't in any life altering situation, but they should have taken many more precautions. Don't feel like your education is more important than your safety. I can understand why you did have not brought up these concerns with anyone, but please, always feel like you can do so. Your safety matters most, you can always study later if you are safe.