In {TAIL ~ operation}, {HEAD ~ tube} 12 is evacuated to a pressure lower than about 0.1 torr, preferably lower than about 0.001 torr, and then sealed 
In { TAIL ~ operation } , { HEAD ~ tube } 12 is evacuated to a pressure lower than about 0.1 torr , preferably lower than about 0.001 torr , and then sealed
REL 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 OTH OTH OTH