Helium (He) Helium is one of the most inert gases and lighter than air. It is used as a cooling media in nuclear reactions and other studies. It is also used as an inert atmosphere for crystal growing. It is used to fill fluorescent lamps and as a leak detection fluid. Zero Grade and UHP Helium are the most commonly used carrier gas for Flame Ionization (FlD) and Thermal Conductivity (TCD) gas chromatography. Liquid Helium is used in cryogenic research.