MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 4 Radon Measurement Systems Quality Assurance Definitions positively charged electret is measured before and after the exposure to radon. During the exposure, radon passively diffuses into the ion chamber and subsequently decays. The radon decay and its short-lived progeny ionize the air inside the chamber. Electrons are attracted to the electret and discharge it. From the surface voltage of the electret measured before and after the exposure, and the duration of the exposure, the average radon concentration during the exposure can be calculated using calibration factors determined through exposures of devices in a STAR . Ambient gamma rays also ionize air inside the chamber, and the effects of ambient gamma radiation must be taken into account. Different electret sensitivities and chamber sizes can be used in combination to measure a range of radon concentration ranging from 2 days to 1 year. The EIC QA requirements apply to all combinations of electrets and chambers used to measure radon concentration in ambient air. In-Control : A measurement system that produces repeatable and stable QC results, including background, instrument stability tests and comparison checks for CRMs; duplicates , spikes and blanks for other methods; and the method-specific checks described in this standard. Note—The QC limits presented in this standard of practice are derived from industry experience and results that are applicable to categories of methods. Each measurement system can develop more restrictive limits than those presented here based on their QC results, which must in all cases be derived by using a method described in the companion handbook (or another statistically defensible control limit generation algorithm) and documented. Until a measurement system derives limits from its own QC results, the limits presented in this standard can be applied to determine data validity. Individual Percent Error (IPE): The degree from which a single measured value (X) deviates from the conventionally true value (T). The IPE is calculated using the following equation: IPE = [100 (X – T) / T] (1) where X = Measured value (Bq/m 3 , pCi/L, Bq-h/m 3 or pCi-d/L) T = Conventionally true value (in the same unit as X) Laboratory Control Sample: A sample of material or a device that has been exposed to a known concentration or infused with known activities of radioanalytes, which is then used in routine procedures to track changes in different components of laboratory operations. Laboratory control samples may be laboratory standards, which are usually defined as an uncontaminated sample matrix that is spiked with known amounts of analytes from a source that is independent from the calibration standards. Lower Limit of Detection, Counting Technology (LLD CT ) Methods (CRM, ATD and CAD): The smallest net count rate at which there is 95% confidence that a signal above background is detected (true positive). The blank count rate and blank counting time are determined by counting a blank sample in the laboratory. For this standard, and for devices that rely on independent event counting technology, this equation by Currie (1968) is used. LLD CT = 2.71/t s + 3.29(R b /t b + R b /t s ) ½ (2) where LLD CT = Lower Limit of Detection (cpm) for counting technology methods t s = Sample counting time (min), or for ATDs, the area of sample scanned (mm 2 ) R b = Background or blank count rate (cpm), or for ATDs, the blank sample track density (tracks/mm 2 ) t b = Background or blank counting time (min), or for ATDs, the area of blank sample scanned (mm 2 ) Note—The LLD for ATD counting systems can use the same formula by using the areas of the plastic counted for blanks and field exposed detectors as surrogates for the background and sample counting times. For CRMs, the sample counting time is the time spent making a radon measurement; the background count rate and