Radioactivity well logging for deter-mining the presence of hydrogen

Claim 1

IN APPARATUS FOR CONDUCTING A NEUTRON GAMMA RAY WELL LOG OF A BORE HOLE COMPRISING A LOGGING INSTRUMENT ADAPTED TO BE PASSED THROUGH A BORE HOLE AND COMPRISING A SOURCE OF NEUTRONS AND A DETECTOR OF GAMMA RAYS WHICH MAY RESULT FROM IRRADIATION OF AN EARTH FORMATION BY NEUTRONS FROM THE SOURCE, THE IMPROVEMENT COMPRISING A SCINTILLATION TYPE GAMMA RAY DETECTOR HAVING A PREDETERMINED QUANTITY OF NEUTRON ABSORBING MATERIAL POSITIONED IN THE VICINITY OF THE DETECTOR AND CHARACTERIZED BY THE EMISSION OF RADIATION TO WHICH THE DETECTOR IS SENSITIVE, 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 TRAVELLING TOWARD SAID DETECTOR, THE QUANTITY OF SAID ABSORBING MATERIAL BEING CHOSEN IN RELATION TO THE INTENSITY AND SPACING FROM SAID SOURCE SUCH THAT RADIATION WILL BE EMITTED THEREFROM IN RESPONSE TO INTERACTION WITH NEUTRONS HAVING AN INTENSITY WHICH SUBSTANTIALLY NEUTRALIZES THE EFFECT OF CHLORINE ON THE NEUTRON GAMMA RAY LOG, SAID SCINTILLATION TYPE DETECTOR HAVING A PULSE AMPLITUDE DISCRIMINATOR ASSOCIATED THEREWITH WHICH IS BIASED TO EXCLUDE AT LEAST THOSE LOWER ENERGY GAMMA RAYS WHICH MAY BE SCATTERED TO THE DETECTOR FROM THE SOURCE.