Uranium is a naturally occurring element that can be found in low levels within all rock, soil, and water. U238 makes up 99% of the Uranium in the world and really isn’t all that radioactive. It IS an alpha source, but the half-life for U238 is over 4 billion years. That means it doesn’t decay very rapidly. U235, on the other hand, is the only fissile isotope occurring in nature… and is almost certainly not going to be found in any substantial quantity in this sample. Leave it in the can and you will be just fine. Just don’t go eating it or anything. 😉