MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 33 Radon Measurement Systems Quality Assurance Laboratories—Alpha Track 10 LAB QA FOR ALPHA TRACK DETECTOR (ATD) METHODS This section applies to the method of counting tracks in alpha-sensitive material. For this method, all requirements in Sections 3 and 7 apply, including laboratory-specific QA/QC training, chain of custody, quality systems , data validation , reporting, calibration , warning and control limits, responsibilities, QC of detector material and minimum intervals between system calibrations . This standard presents limits on QC results that are applicable to all configurations and are defined by the combination of chamber, plastic and the etching and counting process. 10.1 ATD Laboratory—Standard Counting Configurations Note 1— Detectors. This type of radon measurement method uses a piece of plastic, typically of either allyl diglycol carbonate or cellulose nitrate, inside an electrically conducting plastic chamber. Radon diffuses passively into the chamber, where it subsequently decays. Alpha particles emitted from radon and two of its short-lived progeny, 218 Po and 214 Po, strike the plastic detector and create damaged volumes or “latent tracks.” The plastic is etched in a caustic solution, which produces tracks that are visible with a microscope, as the latent tracks are more soluble than the surrounding undamaged material in such a solution. Note 2— Analysis. ATD analysis uses a microscope or computer optic system to determine the track density in tracks/mm 2 . A calibration factor, determined through device exposures in a STAR , is used to convert the track density to a value of integrated concentration in Bq-h/m 3 or pCi-d/L. After subtracting the background track density that is appropriate to the batch of plastic, the average radon concentration during the exposure is determined by dividing the integrated concentration by the length of the exposure time. Each ATD configuration is associated with different exposure periods, such as 90– 365 days, with some ATD configurations effective for time periods as short as 10 days. 10.2 ATD Laboratory—QC of ATD Materials 10.2.1 Alpha-Sensitive Plastic and Etchant Laboratories are to measure background track density and its variability in at least 5% of the detectors made from each batch . Background track density is used in the algorithm (1) to generate radon concentration from the exposed detector counts from the same batch , and (2) to generate the lower limit of detection (from background within- batch variability), which is then translated to MDC using the calibration relationship. In addition to being used in the algorithm to generate radon concentration from the track density, the variability in background tracks is to be tracked and analyzed using control charts as a QC measure to identify changes in the measurement system. Some laboratories arrange for testing and certification (e.g., ASTM STP 643 [ASTM International 1978]) to assess plastic components used in the detectors. Etchant characteristics are to be within QAP- specified limits and may be purchased as certified to be within those limits. Limits on the range and variability of material characteristics can be set by the laboratory if the results of the QC tests, including chamber-exposed spikes conducted at a rate of 3% of the tests conducted, meet the lower limit of detection , imprecision, total error and proportionality requirements of the ANSI/AARST MS-PC standard. 10.2.2 ATD Laboratory—Storage of Alpha-sensitive Materials Because any radon exposure can cause tracks, shipping and handling procedures are to provide as little air exposure as possible except to the environment being tested. Especially for configurations that allow shorter term exposures, background track accrual and the variability in background (tracks accrued in all