Mud-cake-thickness measuring device for gamma-gamma density logger

Claim 1

IN A LOGGING SONDE FOR INVESTIVATING THE BULK DENSITY OF AN EARTH FORMATION TRAVERSED BY AN IRREGULAR BOREHOLE AND WHEREIN SAID SONDE INCLUDES A BODY PORTION CONTAINING A GAMMA-RADIATION SOURCE, GAMMA-RADIATION DETECTING MEANS SPACED A PREDETERMINED DISTANCE FROM SAID SOURCE, SHIELDING MEANS BETWEEN SAID SOURCE AND DETECTOR, COLLIMATING MEANS FOR RESTRICTING BOTH THE PATH OF SAID GAMMA RADIATION ENTERING INTO AND RETURNING FROM SAID FORMATION AND SPRING MEANS SECURED TO SAID BODY PORTION FOR URGING SAID SONDE INTO ENGAGEMENT WITH THE SAME SIDE OF SAID BOREHOLE TO WHICH SAID COLLIMATING MEANS ARE DIRECTED, THE IMPROVEMENT FOR DETERMINING THE IRREGULARITIES OF SAID BOREHOLE LYING DIRECTLY BETWEEN SAID DETECTOR COLLIMATING MEANS AND SAID SOURCE COLLIMATING MEANS COMPRISING A SCIMITAR-SHAPED KNIFE BLADE PIVOTALLY SUPPORTED AT ONE END BETWEEN SAID SOURCE AND SAID DETECTOR, THE OTHER END OF SAID BLADE INCLUDING A KNIFE EDGE FOR PENETRATING THE MUD CAKE ON THE SIDE WALL OF SAID BOREHOLE, ADDITIONAL SPRING MEANS FOR BIASING SAID EDGE OF SAID KNIFE BLADE TOWARD THE ROCK FORMING THE SIDE WALL OF SAID BOREHOLE AND TOWARD THE SAME SIDE AS SIDE SONDE IS BIASED BY SAID BODY URGING SPRING MEANS, MEANS FOR MEASURING THE PIVOTAL DEFLECTION OF SAID KNIFE BLADE RELATIVE TO THE BODY PORTION OF SAID LOGGING SONDE, MEANS FOR CONVERTING SAID PIVOTAL DEFLECTION OF SAID BLADE TO AN ELECTRICAL