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Thirty-four laboratories from 13 countries took part in the 2011 HPA (now part of PHE) intercomparison. Some laboratories submitted more than 1 set of detectors, so 39 sets of detectors were exposed together in the radon chamber. Each participant was asked to return results for each detector. In total, 33 laboratories reported results for 38 sets.
A new exposure scheme was introduced to provide a better measure of the detectors response over specified range and a measurement error was used in the new ranking system, which evaluated the performance for each exposure separately.