The most widely used scintillation material for gamma-ray spectroscopy is Sodium Iodide, NaI(Tl).   It is hygroscopic and is only used in hermetically sealed metal containers to preserve its properties. All water-soluble scintillation materials should be packaged in such a way that they are not attacked by moisture. Some scintillation crystals may easily crack or cleave under mechanical pressure whereas others are plastic and only will deform like CsI(Tl). See our Table of Properties or Table of Applications for material specific comments.