Optimum Method to Determine Gamma Activity in 200 Liter Drums – In-toto Measurement or Extracting a Sample

In the process of decommissioning contaminated facilities, and in the conduct of normal operations involving radioactive material, it is frequently required to measure radioactivity in large containers such as 200 liter drums. For solid material, it is quite unusual for the radioactivity to be homogeneously distributed throughout the container. One way to derive the concentration of radioactivity within the container is to extract a sample for subsequent measurement in the laboratory. Another way is to use gamma spectroscopy and assay the entire container, or in-toto measurement. This paper examines the process of determining the best way to estimate the activity within the container, and gives quantitative estimates of measurement uncertainty for various conditions of radioactivity contained within 200 liter drums. When the contents of the container are not homogeneous, the sampling uncertainty is likely to be larger than the in-toto measurement uncertainty.