REEVALUATION OF THE IDENTIFICATION PERFORMANCE OF HANDHELD RADIOISOTOPE IDENTIFIERS (RIIDs)

Since the events of 9/11, handheld radioisotope identifiers are increasingly used across the United States, by state, local, and federal agencies to detect and identify possible radiological threats. The ability of a handheld radioisotope identifier (RIID) to detect and correctly identify radioactive material via its gamma-ray signature is dependent on several factors, including but not limited to crystal type, crystal size, count time, background interference, intervening materials and identification algorithms. Controlled variables such as, distance and shielding, will be used to test the performance of each radioisotope detector. A five category matrix to score the performance of each radioisotope identifier against a variety of Naturally Occurring Radioactive Material (NORM), industrial, medical and Special Nuclear Material (SNM) sources was developed. The five category system: correct, conditionally correct, minor daughter, false negative and false positive, (see “Methodology” section for definitions) allows for a straightforward evaluation of an instrument’s identification performance. We report on the current status and performance of handheld radioisotope identifiers as a cohort and compare our findings to work previously performed at Los Alamos National Laboratory prior to 2005.