{TAIL ~ A dilution gas} for {HEAD ~ use} at the time of forming the surface layer is made of hydrogen , argon or helium or the like 
{ TAIL ~ A dilution gas } for { HEAD ~ use } at the time of forming the surface layer is made of hydrogen , argon or helium or the like
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH