MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 28 Radon Measurement Systems Quality Assurance Laboratories—CAD / Gamma Spectroscopy 8 LAB QA FOR CHARCOAL ADSORPTION DEVICES—GAMMA SPECTROSCOPY METHODS This section applies to the gamma counting method of analyzing charcoal adsorption devices. All requirements in Sections 3 and 7 apply to this method, including laboratory-specific QA/QC training, chain of custody, data validation , reporting, calibration , warning and control limits, responsibilities, QC of detector material and minimum intervals between system calibrations . 8.1 CAD / Gamma Spectroscopy—Standard Counting Configurations Note—Common systems for analyzing activated carbon adsorption detectors include: — 3” by 3” NaI (Tl) or other gamma-ray detector and photomultiplier, — At least 5 cm of lead shielding that completely surrounds each detector, — High-voltage power supply, — Pre-amplifier and amplifier, — Single- or multi-channel analyzer and scaler, — Timing system, — Standard counting configurations, placement jigs and procedures to standardize the counting geometry as much as possible and — Gravimetric scale that measures the device mass before and after exposure. 8.1.1 Equipment Maintenance All system components are to be routinely maintained and verified for functionality when operating to analyze detectors. Concerns are to be logged and relayed to the quality manager or persons responsible for data validation of test results. 8.1.2 Gravimetric Scale Requirements The measurement error of the scale, as listed on the scale manufacturer documentation, shall not exceed 0.01 g, and the scale shall be recalibrated at least annually in accordance with manufacturer recommendations. In addition, at least one documented counting session-specific QC check is to be conducted with at least one standard weight, compared to tolerance limits, repeated when outside the limits, documented as part of each counting session QC log and corrective action implemented when warranted. Note—Section 18.6.7 of the Multi-Agency Radiological Laboratory Analytical Protocols Manual (MARLAP) (U.S. EPA et al. 2004) provides guidance on control, calibration and maintenance of calibration instruments that are used for mass measurements. 8.2 CAD / Gamma Spectroscopy—QC of Detector Materials Gamma emitters in the energy region of interest that are inherent in the unexposed charcoal can vary from batch to batch . It is the laboratory’s responsibility to measure and track the background and efficiency associated with different batches using device serial numbers. The background count rate from one or a set of background counts on each counter is to be subtracted from the gross counts of exposed devices prior to applying the calibration relationship described in Section 8.3 . This information aids staff and users of these detectors during investigations of imprecision, failed spikes or failed blanks with successive results higher than the MDC. Finally, variability in background counts is necessary to determine the MDC. Concerns regarding the integrity of closure for detector packaging are to be logged and relayed to staff who are responsible for the integrity of detectors.