Year
2014
Abstract
There is often a need for measuring small samples in association with field surveys especially in situations where the activity consists mainly of particles or when measuring large waste containers such as 200 L drums and B25 boxes. The ORTEC ISO-CART-85 systems were developed to provide container counting and radiation surveys with precise nuclide identification and quantification, especially when the container content is not well known. In the ISOPLUS software, the HPGe detector efficiency and gamma ray attenuation are modelled from a calibrated point source measurement and general descriptions of the container and matrix. In 2009, the model was improved for close detector – container geometries. Recently the ISO- CART-85 was introduced which incorporates a very large area (~5700 sq mm) HPGe crystal of ~50% relative efficiency, and is designed to provide free release sensitivities in a mobile system. The revised ISO-CART-85 now includes a graded – Z shield with extension, top, and plastic source positioners to accommodate 1 liter bottles a few cm from the detector endcap. It is intended to be operated with the detector face orientated vertically upwards. This was to allow the in-field measurement of bulk or “grab” samples of material such as soils, concrete dusts, or water. To determine the efficacy of the system, samples of different matrices, fill levels, and nuclides were measured using the standard ORTEC ISOPLUS calibrated using a point source and the absorption correction for containers. The analysis activity results were compared to the known activities of certified standards, known natural activity concentrations, and to GammaVision analysis results for simple geometries and matrices for a range of nuclides with gamma rays from 60 to 2000 keV. The Minimum Detectable Activity was also measured. The results show the system can produce results of value and within 5 – 10% of the known value depending on the nuclides and matrix. Detailed results and measurement descriptions will be presented.