Spinthariscopes

Back in the day, in high school, we would directly observe radioactive scintillation -- individual nuclear disintegrations -- through a spinthariscope. Today, I still remember using one. They are generally thought to be safe, although they pose a radiation risk if they are damaged or broken. Here and in the USA, they must now be licensed. In the UK, I think, one may still find them "knocking about" in schools.