We now certain kinds of radiation are dangerous, but it is a danger we can’t see. Unless, that is, we use a device called a cloud chamber. The radiation causes trails in the super cooled alcohol vapor inside the chamber and we can see the emissions of radiation from a sample. Below is a sample of Uranium (Pitchblende).

To see how this was done, the following video shows the whole process.

via: IFLScience

Thanks Matt!