Beams and produced by helium neon gas lasers and are directed at photoacoustic absorption cells and containing {HEAD ~ a flowing sample gas stream} recovered from coal, {TAIL ~ oil} and natural gas well drilling 
recovered from
Beams and produced by helium neon gas lasers and are directed at photoacoustic absorption cells and containing { HEAD ~ a flowing sample gas stream } recovered from coal , { TAIL ~ oil } and natural gas well drilling
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH