Thickness measuring apparatus utilizing gamma radiation

Claim 1

IN A DEVICE FOR DETERMINING THE WALL THICKNESS OF A TUBULAR MEMBER, THE COMBINATION OF A PENETRATING RAY SOURCE DISPOSED OUTSIDE SAID TUBULAR MEMBER TO DIRECT A PENETRATING RAY DIAMETRICALLY THROUGH THE TUBULAR MEMBER, DETECTOR MEANS DISPOSED ON THE OPPOSITE SIDE FROM SAID SOURCE IN THE PATH OF SAID RAY AND OPERATIVE TO PRODUCE A SIGNAL HAVING BOTH A.C. AND D.C. COMPONENTS WHICH SIGNAL IS A FUNCTION OF THE STRENGTH OF THE RAY, SAID SOURCE AND DETECTOR MEANS BEING DISPOSED FOR RELATIVE ROTATION WITH RESPECT TO SAID TUBULAR MEMBER ABOUT THE AXIS OF THE TUBULAR MEMBER, CIRCUIT MEANS OPERABLY CONNECTED TO SAID DETECTOR MEANS AND EFFECTIVE TO MODIFY BY THE FACTOR OF THREE THE RELATIVE AMPLITUDE OF THE D.C. AND THE A.C. COMPONENTS IN THE DIRECTION OF REDUCTION OF THE AMPLITUDE OF THE D.C. RELATIVE TO THE A.C., WHEREBY THE SAME AMPLITUDE OF SAID D.C. AND A.C. COMPONENTS BECOME INDICATIVE OF THE SAME WALL THICKNESS, AND MEANS FOR INDICATING THE RESULTING SIGNAL DERIVED FROM SAID CIRCUIT MEANS.