Because {TAIL ~ the vacuum pump} 12 creates {HEAD ~ a vacuum} inside the light source chamber 10, X rays generated and propagating inside the chamber are not attenuated 
Because { TAIL ~ the vacuum pump } 12 creates { HEAD ~ a vacuum } inside the light source chamber 10 , X rays generated and propagating inside the chamber are not attenuated
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH