Radiation measuring system and method

Claim 1

A RADIOACTIVE WELL LOGGING SYSTEM FOR LOGGING THE FORMATIONS TRAVERSED BY A BOREHOLE COMPRISING: A BOREHOLE UNIT INCLUDING A NEUTRON SOURCE FOR IRRADIATING THE FORMATION WITH PULSES OF NEUTRONS SPACED IN TIME FOR THE PRODUCTION OF SECONDARY RADIATION, A DETECTOR FOR DETECTING SECONDARY RADIATION PASSING FROM THE FORMATIONS INTO THE BOREHOLE AND FOR PRODUCING FIRST FUNCTIONS REPRESENTATIVE OF THE SECONDARY RADIATION DETECTED, MEANS FOR CONTINUOUSLY MOVING SAID UNIT INCLUDING SAID SOURCE AND DETECTOR ALONG THE BOREHOLE, A SELECTION CIRCUIT INCLUDING: FIRST AND SECOND DISCRIMINATING MEANS, A TIME-TOPULSE HEIGHT CONVERTER, THE OUTPUT OF SAID DETECTOR BEING APPLIED TO SAID TIME-TO-PULSE HEIGHT'' CONVERTER, SAID TIME-TO-PULSE HEIGHT CONVERTER PRODUCING AN OUTPUT OF PULSES HAVING HEIGHTS PROPORTIONAL TO THE TIME THAT SECONDARY RADIATION IS DETECTED, THE OUTPUT OF SAID TIME-TO-PULSE HEIGHT CONVERTER BEING APPLIED TO SAID DISCRIMINATING MEANS, SAID DISCRIMINATING MEANS BEING SELECTIVELY RESPONSIVE TO PREDETERMINED MAGNITUDES OF SAID PULSES FOR PRODUCING AT THE OUTPUT THEREOF SECOND AND THIRD FUNCTION REPRESENTATIVE OF RADIATION DETECT WITHIN FIRST AND SECOND TIME PERIODS FOLLOWING EACH PULSE OF PRIMARY RADIATION, MEANS RESPONSIVE TO SAID SECOND AND THIRD FUNCTIONS FOR PRODUCING FIRST AND SECOND SIGNALS REPRESENTATIVE OF THE INTENSITY OF SECONDARY RADIATION DETECTED WITHIN SAID FIRST AND SECOND TIME PERIODS, MEANS FOR MODIFYING ONE OF SAID FIRST AND SECOND SIGNALS BY A FACTOR EQUAL TO A RATIO DESIRED TO BE MAINTAINED BETWEEN SAID FIRST AND SECOND SIGNALS, MEANS FOR COMPARING THE MODIFIED SIGNAL AND THE OTHER OF SAID FIRST AND SECOND SIGNALS, MEANS RESPONSIVE TO THE OUTPUT OF SAID COMPARING MEANS FOR VARYING THE RESPONSE OF SAID SELECTION CIRCUIT FOR MAINTAINING CONSTANT THE RATIO DESIRED BETWEEN SAID FIRST AND SECOND SIGNALS, AND A RECORDER RESPONSIVE TO THE OUTPUT OF SAID COMPARING MEANS FOR PRODUCING A LOG CONTINUOUSLY AND IN CORRELATION WITH DEPTH OF SAID BOREHOLE UNIT IN SAID BOREHOLE AND RELATED TO THE DECAY OF SECONDARY RADIATION DETECTED.