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25 July 2008

A GPS-Based System for Radium Contamination Gamma Scanning

R. Meyer; C. Little; M. Shields; S. Green; J. Johnson; and M. Vidyasagar (MFG Inc.)

Shepherd-Miller Inc. (now MFG Inc.) developed a hand-held Global Positioning System (GPS)-based gamma scanning technique for use during preliminary characterization at a 16-square-km in-situ-leach uranium mine in central Kazakhstan. Since that time, the system has been enhanced and used at eight radium/uranium-contaminated sites in the western U.S. At one former uranium mill site in Texas, data acquisition has occurred at a rate of seven acres/hour, with nearly 100% coverage over the 600 acre site. Several million individual latitude, longitude and gamma exposure rate readings are taken at a typical site. The current system, using handheld PDA/GPS units and two inch sodium iodide detectors, is easily hand-carried, or multiple systems may be installed on a four wheel drive platform. All measurements utilize vendor-calibrated scintillator systems; data are stored in digital format. Composite soil samples (10-20 aliquots from a limited number of 10x10 m areas distributed over the site), are independently analyzed for Ra-226. Where site history indicates that disequilibrium between radium and uranium is likely, laboratory analysis for U-238 is also performed, since uranium concentration in soil cannot be evaluated directly. Ra-226 vendor laboratory data are plotted to establish a “cut-off” gamma exposure rate for each site. A key aspect of system performance has been the development of reliable data links and software. The system is being used extensively for initial evaluation of remedial action sites. Control scans are then performed as remedial action proceeds. A final scan is developed after earth removal is completed, to create an output plot showing gamma levels and equivalent Ra-226 concentrations. Our experience at completed sites indicates very favorable regulatory agency reponse to the comprehensive, quality-controlled data plots developed using the system.

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