Hidden explosives detector utilizing long-lived radioactive tracer material

Claim 1

APPARATUS FOR DETECTION OF EXPLOSIVES HIDDEN ON PERSONS OR IN LUGGAGE IN WHICH THE EXPLOSIVE HAS BEEN SEEDED WITH A LONG-LIFE LOW-ACTIVITY RADIOACTIVE TRACER WHICH SIMULTANEOUSLY EMITS TWO SUBSTANTIALLY EQUAL ENERGY GAMMA RAYS IN CASCADE AND IN WHICH THE PERSON OR LUGGAGE MOVES DOWN A PATHWAY, COMPRISING FIRST AND SECOND DETECTORS POSITIONED ON ONE SIDE OF THE PATHWAY SPACED FROM EACH OTHER IN THE DIRECTION OF MOVEMENT; THIRD AND FOURTH DETECTORS POSITIONED ON THE OTHER SIDE OF THE PATHWAY OPPOSITE SAID FIRST AND SECOND DETECTORS RESPECTIVELY; EACH DETECTOR INCLUDING A LARGE TANK HAVING A LIQUID SCINTILLATOR, AND A PLURALITY OF PHOTOMULTIPLIERS ARRANGED WITH THEIR PHOTOEMISSIVE CATHODES POSITIONED ADJACENT THE SCINTILLATOR TANK AND THEIR ELECTRICAL OUTPUT TERMINALS COMMONLY CONNECTED TO A SINGLE OUTPUT TERMINAL FOR EACH DETECTOR; FIRST AND SECOND OR CIRCUIT MEANS, EACH HAVING TWO INPUT TERMINALS AND ONE OUTPUT TERMINAL FOR PASSING A PULSE AT EACH OF SAID INPUT TERMINALS TO SAID OUTPUT TERMINAL, MEANS FOR CONNECTING THE OUTPUT OF THE FIRST DETECTOR TO ONE INPUT TERMINAL OF THE FIRST OR CIRCUIT, MEANS FOR CONNECTING THE OUTPUT OF THE FOURTH DETECTOR TO THE OTHER INPUT TERMINAL OF THE FIRST OR CIRCUIT; MEANS FOR CONNECTING THE OUTPUT OF THE SECOND DETECTOR TO ONE INPUT TERMINAL OF THE SECOND OR CIRCUIT; MEANS FOR CONNECTING THE OUTPUT OF THE THIRD DETECTOR TO THE OTHER INPUT TERMINAL OF THE SECOND OR CIRCUIT; COINCIDENCE DETECTION MEANS HAVING TWO INPUT TERMINALS AND AN OUTPUT TERMINAL; COUNTING MEANS CONNECTED TO SAID COINCIDENCE OUTPUT TERMINAL; ONE LOW-LEVEL AMPLITUDE DISCRIMINATOR MEANS HAVING AN INPUT CONNECTED TO THE OUTPUT TERMINAL OF THE FIRST OR CIRCUIT AND HAVING AN OUTPUT TERMINAL CONNECTED TO ONE OF THE COINCIDENCE INPUT TERMINALS; ANOTHER LOW-LEVEL AMPLITUDE DISCRIMINATOR HAVING AN INPUT CONNECTED TO THE OUTPUT TERMINAL OF THE SECOND OR CIRCUIT AND HAVING AN OUTPUT CONNECTED TO THE OTHER COINCIDENCE INPUT TERMINAL; ONE HIGH-LEVEL DISCRIMINATOR HAVING AN INPUT TERMINAL AND AN OUTPUT TERMINAL WITH THE INPUT TERMINAL CONNECTED TO THE OUTPUT OF THE FIRST OR CIRCUIT; ANTI-COINCIDENCE MEANS CONNECTED TO SAID COINCIDENCE MEANS AND SAID HIGH-LEVEL DISCRIMINATOR FOR PREVENTING OUTPUT PULSES FROM SAID COINCIDENCE MEANS WHEN A PULSE EXISTS AT THE OUTPUT OF THE HIGH-LEVEL DISCRIMINATOR; SAID HIGH-AND-LOW-LEVEL DISCRIMINATOR CIRCUITS PROVIDING OUTPUT PULSES HAVING A WIDTH OF LESS THAN 10**-6 SECONDS WHEREBY GAMMA RAYS ARE COUNTED ONLY WHEN IN COINCIDENCE WITHIN A VERY SHORT TIME AND WHEN THE AMPLITUDE IS BETWEEN THE HIGH AND LOW ENERGY LEVELS; SAID COINCIDENCE CIRCUIT INCLUDES FIRST AND SECOND DIODES AND SAID ANTI-COINCIDENCE CIRCUIT INCLUDES A THIRD DIODE, MEANS FOR CONNECTING SAID THREE DIODES IN PARALLEL TO SAID COINCIDENCE OUTPUT TERMINAL, A SOURCE OF POWER, A RESISTOR CONNECTING SAID COINCIDENT OUTPUT TERMINAL TO SAID SOURCE OF POWER; SAID DIODES BEING POLED FOR NORMALLY CONDUCTING TO SAID SOURCE OF POWER; MEANS FOR CONNECTING THE OUTPUT OF SAID HIGHCONDUCTION; MEANS FOR CONNECTING THE OUTPUT OF SAID HIGHLEVEL DISCRIMINATOR CIRCUIT FOR REVERSING THE STATE OF CONDUCTION OF THE THIRD DIODE; MEANS FOR CONNECTING ONE OF THE COINCIDENT INPUT TERMINAL TO THE FIRST DIODE AND THE OTHER COINCIDENT INPUT TERMINAL TO THE SECOND DIODE FOR REVERSING THEIR CONDUCTIVE STATE UPON THE OCCURRENCE OF A PULSE AT THE INPUT TERMINALS WHEREBY THE OCCURRENCE OF PULSES AT BOTH COINCIDENT INPUT TERMINALS WILL RESULT IN A PULSE AT THE COINCIDENT OUTPUT TERMINAL UNLESS A PULSE OCCURS AT THE ANTI-COINCIDENCE CIRCUIT.