LIMITED-SCAN BACKSCATTER TECHNIQUE FOR DETECTION OF HIDDEN CORROSION

WE PROPOSE TO INVESTIGATE IN PHASE I A VOLUME-SPECIFIC, LIMITED-SCAN PHOTON BACKSCATTER TECHNIQUE FOR THE DETECTION OF LOCALIZED CHANGES IN COMPOSITION AND/OR THICKNESS OF A LAYER HIDDEN UNDER A SURFACE LAYER, AS A GENERIC ANALOGUE OFTHE HIDDEN CORROSION PROBLEM. FEATURES INHERENT IN THE WELL-ESTABLISHED GAMMA-RAY BACKSCATTER DENSITY GAUGE CONCEPTS AND IN BACKSCATTER IMAGING TOMOGRAPHY INDICATE THATA METHOD BASED ON PHOTON BACKSCATTER IS AN EXCELLENT CANDIDATE FOR THE DETECTION OF HIDDEN CORROSION, IF JUDICIOUSLY EMPLOYED. PRELIMINARY CALCULATIONS, DESCRIBED IN THE PROPOSAL, DEMONSTRATE THAT SMALL LOCAL CHANGES IN THICKNESS OR COMPOSITION CAN BE DETECTED VIA CHANGES IN THE BACKSCATTERED SIGNAL, IF THE SOURCE AND DETECTOR COLLIMATION, SOURCE ENERGY, AND PLACEMENT OF THE SOURCE-OBJECT-DETECTOR ARE PROPERLY SELECTED. IN PHASE I, WE PROPOSE TO INVESTIGATE, BOTH ANALYTICALLY AND EXPERIMENTALLY, THE RELATIONSHIP BETWEEN THESE PARAMETERS AND THE SENSITIVITY OF THE BACKSCATTERED RESPONSE AND THE SCAN STEP-SIZE REQUIREMENTS FOR DETECTING THE PRESENCE OF INDICATORS OF HIDDEN CORROSION. RESULTS OF THIS INVESTIGATION WILL DEMONSTRATE THE FEASIBILITY OF THE TECHNIQUE WHICH, IF SUCCESSFUL, WILL BE IMPLEMENTED IN A PROTOTYPE GAUGE IN PHASE II; SUCH A GUAGE WILL BE RUGGED, INEXPENSIVE, SAFE, AND EASY TO OPERATE.