ABSTRACT

Radiological characterization in DD & ER projects is an important part of the project. When properly applied it can provide much needed information to better plan the project, to guide the progress of the remediation, to know when to stop remediating, and to prove officially that the job is complete. One of the more expensive radiological characterization tasks is the location and quantification of hidden or buried sources. Many samples must normally be taken for laboratory analysis, which is costly and takes much time. With the newly available InSitu gamma spectroscopy systems, this can often be done in the field. InSitu gamma spectroscopy avoids the dose and industrial hazard of extracting samples, avoids the necessity of packaging and transporting to fixed laboratories, gives results nearly immediately, and generates no waste. Reactors facilities [operating or shut down], Uranium processing facilities, NORM contamination sites, and weapons sites all have nuclides that are amenable to InSitu Ge gamma spectroscopy. Applications include locating and quantifying surface contamination on floors and walls; locating and quantifying subsurface items like pipes and drums; determining the fill height and activity inside closed containers like drums, boxes, and pipes; and determining the activity-depth profile of neutron-activation without taking samples. The key to determining the location of radionuclides is the variation of the radioactive emissions as a function of energy, distance, angle, absorber material, absorber thickness. Measurements at different energies, angles, distances from an object, when analyzed as a group can tell the location of the radioactivity within the object. To make this process convenient and practical, fast and accurate mathematical efficiency calibration tools are needed. The efficiency calibration software supplied with the Canberra ISOCS system is one such method. Multiple calibrations are made quickly with the software to determine the efficiency variation for each of the multiple energy lines and/or measurements of the object. The correct source location can be determined by iterative manual computations, by large numbers or random computations, or by matrix analysis methods.