Nuclear well logging method and apparatus

Claim 1

A WELL LOGGING METHOD FOR DISTINGUISHING THE DEPTH AT WHICH AN HYDROGENOUS EARTH FORMATION TRAVERSED BY A BOREHOLE CONTAINS A CHARACTERISTIC SUBSTANCE HAVING A NUETRON CAPTURE CROSS SECTION THAT IS APPRECIABLY HIGHER THAN THE NUETRON CAPTURE CROSS SECTION OF HYDROGEN FROM THOSE DEPTHS AT WHICH SAID FORMATION DOES NOT CONTAIN SAID SUBSTANCE COMPRISING THE STEPS OF, BOMBARING THE FORMATION WITH NUETRONS, MEASURING THE INTENSITY OF THE NEUTRON RAYS OF SUBSTANAILLY THERMAL ENERGY EMANATED FROM SAID FORMATION RESPONSIVELY TO SUCH BOMBARMENT, SIMULTANEOUSLY MEASURING THE INTENSITY OF GAMMA RAYS OF CAPTURE HAVING ENERGIES IN THE NEIGHBORHOOD OF 7 MEV EMANATED FROM SAID FORMATION RESPONSIVELY TO SUCH BOMBARDMENT, RECORDING SAID INTENSITIES ON A COMMON RECORD IN CORRELATION WITH DEPTH, AND COMPARING SAID INTENSITIES TO LOCATE REGIONS WHEREIN THE PRESENCE OF SAID SUBSTANCE CAUSES AN INCREASE IN THE INTENSITY OF SAID GAMMA RAYS OF CAPTURE RELATIVE TO THE INTENSITY THEREOF IF SAID SUBSTANCE IS ABSENT FROM THE FORMATION AND ALSO CAUSES A DECREASE IN THE INTENSITY OF SAID MEASURED NEUTRONS RELATIVE