Patent ID: 8410451

Claim:
A method for interrogating a remote target ( 16 ) with slow neutrons ( 10 ) to produce gamma ray fluorescence from targets that contain at least one specified substance of interest, said method comprising the steps of: providing a remotely located target ( 16 ); providing a slow neutron source ( 12 ) capable of generating at least one of thermal, epithermal, and cold neutrons, the neutron source ( 12 ) having power ON and OFF modes, the neutron source ( 12 ) operable in its ON mode to emit neutrons ( 10 ) capable of traveling over time and distance to reach the target ( 16 ) and there produce gamma rays of interest ( 18 ) upon interaction with a substance of interest, the travel time of the emitted neutrons ( 10 ) to the target ( 16 ) defining a neutron time of flight (NTOF); providing a gamma ray detector ( 14 ) proximate the neutron source ( 12 ), the gamma ray detector ( 14 ) having power ON and OFF modes and operable in its ON mode to detect gamma ray signals ( 18 - 22 ); powering ON the neutron source ( 12 ) for a pulse period and then powering OFF the neutron source ( 12 ); and constraining the gamma ray detector ( 14 ) in its OFF mode during the pulse period and for an immediately subsequent additional period of time generally equal to the NTOF, and then powering ON the gamma ray detector ( 14 ), whereby any unwanted nuisance gamma signals ( 20 , 22 ) arriving at the detector ( 14 ) during the pulse period and during the subsequent NTOF period are not detected.