Radium consists of 16 isotopes, the most abundant being the Radioactive Radium-226. This is a metallic substance, has a Half-Life of 1602 years and Decays via a complicated chain, eventually leading to stable Lead-206. Along the way it decays to Radon Gas (Rn-222). Radium was isolated from pitchblende in 1898 by Marie and Pierre Curie. The activity of 1g of radium was used to define the activity unit, the Curie (Ci). Radium is difficult to shield needing significant quantities of lead. In addition, radium contaminated dust is a particular inhalation hazard due to its abundant Alpha Particle decay.