Discovered : by F.E. Dorn Isolated in Halle, Germany Origin : The name is derived from radium. Description : Radon was first discovered as the gas produced from radium as it decayed in sealed ampoules. It is colourless and odourless, and is chemically inert, but it is dangerous because it gives off alpha rays. There is a detectable amount in the atmosphere, and concentrations can build up indoors in certain localities. Image : Radon home.