The X rays are emitted in response to {TAIL ~ an impinging beam}, such as an electron beam, directed towards {HEAD ~ the sample surface} where a defect resides 
The X rays are emitted in response to { TAIL ~ an impinging beam } , such as an electron beam , directed towards { HEAD ~ the sample surface } where a defect resides
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH