Typical carrier gases include helium, nitrogen, argon, hydrogen and air. The bulbs are under vacuum or filled with argon, krypton or xenon. Clathrate formation can be used to fractionally distill xenon, argon and krypton. The fluid is periodically purged with helium gas which would remove the argon. Hydrogen, argon, ammonia and nitrogen can be used as propellant. Noble liquid detectors detect scintillation produced by a particle collision in liquid xenon or argon. Modern computer rooms use combinations of inert gases such as Nitrogen, Argon and CO2. Mixtures of argon, carbon dioxide and oxygen are marketed for welding steels. Krypton costs about 100 times as much as argon. As of 2008, endohedral complexes with helium, neon, argon, krypton, and xenon have been created. White and gold can also be created with adding argon and helium. Other gasses like hydrogen or Argon are also used. It can be handled only under inert gas, such as argon. Thus, chemical n-doping must be performed in an environment of inert gas (e.g., argon). Acceleration energies for gases such as argon are typically a few kilovolts.