MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 5 Radon Measurement Systems Quality Assurance Definitions counting time are determined when measuring an atmosphere free of radon, such as nitrogen or aged air. For CADs, the sample counting time is the time spent counting the sample in the laboratory. Lower Limit of Detection, Non-Counting Technology (LLD NCT ) Methods: The EIC method does not count detected radioactive decay events, but the LLD for such methods is calculated to provide the same assurance: the smallest signal at which there is 95% confidence that a signal above background is detected (true positive). EIC methods use the difference between the two voltage measurements (final subtracted from initial with the uncertainty in each voltage determination being independent of both the concentration and one another). Therefore, the combined variance is given by the sum of the variances in both the initial and final voltage, which follows the traditional root-sum-of-the-squares of sample standard deviations of both measurements. Assuming that both voltage determinations have equal variances, and using the square of sample standard deviation as the variance, results in the combined standard uncertainty in the net voltage of: Uncertainty in net voltage loss = ! #$% + #(% (3) If both voltage determinations are assumed to have equal variances ( s *% ), then the uncertainty in net voltage loss given by the combined uncertainty of the two analyses is given by √2 ∗ s * If the mean background voltage loss m / is zero, as there should be zero voltage loss in EICs stored with the sensitive plastic prevented from discharge using a “keeper cap,” this reduces to: LLD NCT = 3.29* √2 ∗ s * or the familiar (4) LLD NCT = 4.65 ∗ s * (5) Matrix Spike: A routine detector that has been exposed to or infused with a known amount of target analyte so that when analyzed the results include any bias that is introduced by the materials used in, or the configuration of, the routine detector. Measurement System : All the components that are involved in the measurement of 222 Rn concentration and that are part of the quality system , including all personnel and equipment associated with providing measurement results. MDC ( Minimum Detectable Concentration) : The lowest concentration that is detectable at an established confidence (95% at minimum). The MDC is derived from the LLD by applying the same factors that are used to convert the net signal to radon concentration or integrated concentration. For a CRM, the MDC is calculated from the LLD using the CRM calibration factor. For CAD methods, the MDC is calculated from the LLD using factors that consider parameters such as the adsorbed moisture, the duration of the exposure, the system counting calibration factor and radioactive decay. MS-PC : Performance Specifications for Instrumentation Systems Designed to Measure Radon Gas in Air (ANSI/AARST MS-PC 2015) specifies that each measurement system demonstrate that when tested in a STAR for the shortest duration recommended by the provider: An individual Relative Percent Error (RPE, also known as Individual Percent Error, or IPE) < ± 25% and a CV of a set of five < 15% in the following tests; • for the temperature test, in a relative humidity of 10–25% and o a temperature of 60 ± 5°F, and o a temperature of 80 ± 5°F; • for the relative humidity test, in a temperature of 65–75°F and o relative humidity of 15–25%, and o relative humidity of 70–80%.