Good morning! welcome back to war! What I have here is the specification of a plastic scintillator named Bicron BC-408, as you see on the technical photo, the source is cesium 137, cobalt 60 and sodium 22 , all high radioactive. If you go on searching, and there's lots for sale at eBay, the sellers will say to you that it will only work if mounted on a PMT , that creates a sort of confusion, PMT photomultiplier detector is based on radiation sources like NA(TI) (encapsulated sodium on lead protecting thallium ) ; anyway, one thing doesn't imply on the other...both this Bicron -408 and the PMT have radioactive sources. The blue colour emission, comes from anthracene , (a component of 20% of carbon at space), specifications like, emission of electrons on the infinite number 10(23) (this is the calculation of infinitive on physics) , and the emission of photons, surely defines this material (plastic) as radioactive.