Radiation source measuring apparatus having automatic background subtract means

Claim 1

APPARATUS FOR MEASURING A RADIATION SOURCE LEVEL IN THE PRESENCE OF A BACKGROUND RADIATION LEVEL COMPRISING THE PULSE GENERATOR MEANS PROVIDING A SOURCE OF SIGNAL PULSES RESPONSIVE TO TOTAL RADIATION LEVEL, TIME BASE GENERATOR MEANS PROVIDING A SOURCE OF TIMING PULSES, COMPUTING MEANS CONNECTED TO EACH OF SAID GENERATOR MEANS AND HAVING AN INDEPENDENT COMPUTING MEANS SIGNAL CHANNEL AND AN INDEPENDENT COMPUTING MEANS TIME PULSE CHANNEL, EACH PROVIDING AN OUTPUT SIGNAL, MEANS IN SAID COMPUTING MEANS SIGNAL CHANNEL FOR PROVIDING AN INSTANTANEOUS COUNT OF SAID SIGNAL PULSES, RADIATION LEVEL MEASURING MEANS CONNECTED TO SAID COMPUTING MEANS SIGNAL CHANNEL RESPONSIVE TO AN OUTPUT SIGNAL THEREFROM, SWITCH MEANS FOR SWITCHING SAID COMPUTING CHANNELS IN A PREDETERMINED MANNER, CONTROL MEANS FOR SIMULTANEOUSLY OPERATING SAID CHANNELS TO OPEN SAID CHANNELS IN RESPONSE TO A START SIGNAL AND TO CLOSE SAID CHANNELS AFTER A PREDETERMINED COUNTING TIME IN RESPONSE TO AN OUTPUT SIGNAL FROM SAID TIME PULSE CHANNEL, BACKGROUND SETTING MEANS FOR ESTABLISHING A PREDETERMINED SIGNAL REPRESENTING A BACKGROUND RADIATION LEVEL OF A GIVEN COUNT, COMPARATOR MEANS EFFECTIVE DURING SAID PREDETERMINED COUNTING TIME TO COMPARE THE VALUE OF THE INSTANTANEOUS SIGNAL PULSE COUNT DETERMINED BY SAID COMPUTING MEANS SIGNAL CHANNEL WITH THE COUNT REPRESENTED BY SAID PREDETERMINED SIGNAL ESTABLISHED BY SAID BACKGROUND SETTING MEANS AND PROVIDE A SIGNAL CHANNEL COMPUTING MEANS REST SIGNAL WHEN THE INSTANTANEOUS SIGNAL PULSE COUNT EQUALS THE COUNT REPRESENTED BY SAID PREDETERMINED SIGNAL, SAID RESET SIGNAL BEING EFFECTIVE TO RESET SAID COMPUTING MEANS SIGNAL CHANNEL TO START A NEW COUNT, WHEREBY THE SIGNAL PULSE COUNTED DURING THE REMAINING PORTION OF SAID PREDETERMINED COUNTING TIME WILL BE PROPORTIONAL TO SAID SOURCE LEVEL.