Minimum detectable activities of contamination control survey equipment

The Instrumentation External Dosimetry (I ED) Section of the Health Physics Department at the Pacific Northwest Laboratory (PNL) has performed a series of tests to determine the ability of portable survey instruments used at Hanford to detect radioactive contamination at levels required by DOE 5480.11. This semi-empirical study combines instrumental, statistical, and human factors as necessary to derive operational detection limits. These threshold detection values have been compared to existing contamination control requirements, and detection deficiencies have been identified when present. Portable survey instruments used on the Hanford Site identify the presence of radioactive surface contamination based on the detection of {alpha}-, {beta}-, {gamma}-, and/or x-radiation. However, except in some unique circumstances, most contamination monitors in use at Hanford are configured to detect either {alpha}-radiation alone or {beta}- and {gamma}-radiation together. Testing was therefore conducted on only these two categories of radiation detection devices. Nevertheless, many of the results obtained are generally applicable to all survey instruments, allowing performance evaluations to be extended to monitoring devices which are exclusively {gamma}- and/or x-ray- sensitive. 6 figs., 2 tabs.