SUBSURFACE INSPECTION WITH X-RAY GENERATED POSITRONS

THE RESEARCHERS PROPOSE TO EXTEND THEIR PREVIOUS WORK IN HIGH-ENERGY X-RAY BACKSCATTER IMAGING TOMOGRAPHY (BIT) TO HIGHER ENERGY RANGES IN ORDER TO ACHIEVE GREATER PENETRATIONDEPTHS. AT ENERGIES GREATER THAN A FEW MEV, THE PREDOMINANTINTERACTION IS NO LONGER COMPTON SCATTERING, BUT PAIR PRODUCTION. SINCE THE RESULTING POSITRONS DO NOT ANNIHILATE(CREATING DETECTABLE 511 KEV RADIATION) AT THE ORIGINAL POINT OF INTERACTION, BUT TRAVEL FORWARD A DISTANCE GREATER THAN THE DESIRED SPATIAL RESOLUTION, THEY NORMALLY LIMIT THEUSEFULNESS OF BIT ABOVE 4 MEV. THEY PROPOSE TO TAKE ADVANTAGE OF THE FAVORABLE ANGULAR DISTRIBUTION OF THE ANNIHILATION RADIATION AND THE DEEPER PENETRATION OF HIGHER-ENERGY PRIMARY BEAMS BY A THREE-DIMENSIONAL DECONVOLUTION PROCESS. THEIR PROPOSAL FOR PHASE I RESEARCH IS A SERIES OF TESTS TO UNDERSTAND THE NATURE OF THE SPATIALDISTRIBUTION; THESE WILL BE PERFORMED WITH A 9 MEV OR 16 MEVLINATRON AT AN EXISTING SITE.