Radioactivity well logging

Claim 1

APPARATUS FOR CONDUCTING A RADIOACTIVITY WELL LOG COMPRISING AN INSTRUMENT HOUSING ADAPTED TO BE PASSED THROUGH A BORE HOLE TRAVERSING A PLURALITY OF EARTH FORMATIONS, A SOURCE OF FAST NEUTRONS POSITIONED AT ONE END OF SAID HOUSING, A FIRST DETECTING UNIT QUANTITATIVELY SENSITIVE TO GAMMA RAYS RETURNING TO THE BORE HOLE AS A RESULT OF IRRADIATION OF THE FORMATION BY NEUTRONS FROM THE SOURCE AND WHICH IS ADAPTED AND ARRANGED TO PROVIDE AN OUTPUT SIGNAL PRIMARILY INDICATIVE OF THE PRESENCE OF HYDROGEN IN SAID FORMATION, SAID DETECTING UNIT COMPRISING A SCINTILLATION TYPE DETECTOR OF GAMMA RAYS AND A PREDETERMINED QUANTITY OF NEUTRON ABSORBING MATERIAL POSITIONED IN THE VICINITY OF SAID DETECTOR, SAID NEUTRON ABSORBING MATERIAL BEING CHARACTERIZED BY THE EMISSION OF RADIATION TO WHICH THE DETECTOR IS SENSITIVE IN RESPONSE TO THE CAPTURE OF A NEUTRON, SAID DETECTOR BEING SUBSTANTIALLY UNSHIELDED WITH RESPECT TO SAID RADIATION EMITTED FROM SAID NEUTRON ABSORBING MATERIAL SUCH THAT SAID DETECTOR IS EXPOSED TO AT LEAST A MAJOR PORTION OF SAID RADIATION EMITTED FROM SAID NEUTRON ABSORBING MATERIAL AND TRAVELING TOWARD SAID DETECTOR, WHEREBY THE FIRST DETECTING UNIT IS SENSITIVE TO BOTH NEUTRON-GAMMA RADIATION EMITTED FROM THE FORMATION AND THERMAL NEUTRON RADIATION EMITTED FROM THE FORMATION AND CAPTURED BY SAID NEUTRON ABSORBING MATERIAL SO THAT THE FIRST DETECTING UNIT IS RENDERED SUBSTANTIALLY INSENSITIVE TO THE PRESENCE OF CHLORINE, A SOURCE OF GAMMA RADIATION POSITIONED AT THE END OF SAID HOUSING REMOTE FROM SAID FAST NEUTRON SOURCE, A SECOND SCINTILLATION TYPE RADIATION DETECTING UNIT POSITIONED WITHIN SAID HOUSING AND BEING ADAPTED TO PROVIDE A SIGNAL PROPORTIONAL TO THE INTENSITY OF GAMMA RADIATION RETURNING TO THE BORE HOLE AS A RESULT OF IRRADIATION BY GAMMA RAYS FROM SAID GAMMA RAY SOURCE.