Beam 142 is interrupted by {HEAD ~ an injection mirror} 144, which is positioned to intersect {TAIL ~ one half} of the beam 142  
is positioned to intersect
Beam 142 is interrupted by { HEAD ~ an injection mirror } 144 , which is positioned to intersect { TAIL ~ one half } of the beam 142
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH