| Penetrating radiation: Radiation that can penetrate the skin and reach internal organs and tissues. Photons (x-rays & gamma rays) and neutrons are penetrating radiations. Alpha and beta particles are not considered penetrating radiation. Photon: A discrete packet of pure electromagnetic energy that, when interacting at the molecular or atomic level, acts more like a particle rather than an energy wave. Photons have no mass and travel at the speed of light. Gamma rays and x-rays are photons. Placards/Placarding: Radioactive lll labels that must be used displayed on the outside of a vehicle for higher quantity devices. Moisture density gauges are Radioactive ll and therefore do not require placarding. DO NOT PLACARD A VEHICLE that is transporting a moisture density gauge as those covered by this website. Proton: A small positively charged particle found in the nucleus. The number of protons in a given atom determines the chemical identity of the element. | 
