b'A representative example relevant to chemical weapons detection is the discrimination of phosgene (COCl2) from cyanogen chloride (CNCl). With traditional prompt gamma-ray neutron activation analysis, these two are nearly indistinguishable due to background from the detected oxygen. Moreover, the intense oxygen lines in the gamma spectra interfere with the strongest nitrogen line, which is usually quite weak, making the latter very difficult to identify. The associated particle technique eliminated oxygen from the CNCl spectrum, which made the nitrogen signal clearly visible. Furthermore, the low oxygen signal from COCl2 remained in its respective spectrum with all the background eliminated. Therefore, the distinction was clear by analyzing the two spectra with no background subtraction or quantitative analysis needed and without any additional run time beyond the standard 1-hour assays typically employed in these scenarios.Measurements of simulated COCl2 (top) and CNCl (bottom) in 4.2 in. mortar projectiles. (a) The spectra obtained from traditional prompt gamma-ray neutron activation analysis look nearly identical. (b) The spectra obtained using the associated particle method eliminates the background oxygen making the two chemicals easily distinguishable.131'