The chamber is maintained at at least a partial vacuum and contains {TAIL ~ an impact responsive sensor} for detecting {HEAD ~ particles} incident thereon 
The chamber is maintained at at least a partial vacuum and contains { TAIL ~ an impact responsive sensor } for detecting { HEAD ~ particles } incident thereon
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH