MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 35 Radon Measurement Systems Quality Assurance Laboratories—Alpha Track Informative advisory —These characterizations should take place at the inception of operations and on an ongoing basis, with documentation available to auditors from credentialing authorities who operate under confidentiality agreements. 10.5 ATD Laboratory—Ongoing In-Control Operations Verification of the processing and analysis system’s (etchant and conditions of the etching process, microscopes, light sources, software, device configurations, recording systems, etc.) stability shall be performed as part of each component’s operation. Note—These checks can be performed by analyzing a specific set of QC detectors or plastic samples that were exposed to a known radon concentration (greater than the detection limit), and which have been designated as laboratory QC samples. Batch -specific QC samples should be available to verify and document in-control analysis operations for detectors that are associated with different batches of detectors, as detectors from different batches may be returned for analysis during the same analysis session. The mean and variability of these QC samples are used to derive laboratory limits to assess when the system operations deviate from in-control operations. 10.5.1 ATD Laboratory—Development and Monitoring Control limits At least 20 determinations are required for the development of control limits consistent with the guidance in Section 7.7 . Processes to be monitored include the stability of at least: a) the etching materials, equipment, sensors and procedures by including at least one laboratory QC sample of material or device (laboratory spike ) with each etching process; b) the analysis equipment and procedures by including at least one laboratory QC device (laboratory spike ) with each counting session; and c) appropriate background subtractions using an ongoing assessment of a background specific to batch and configuration. 10.5.2 ATD Laboratory—Laboratory QC Samples in Etching and Counting Processes ATD analysis is to include counting control detectors with known track densities as part of every laboratory process and with each analysis session. Control samples are obtained by exposing plastic or assembled devices in known radon concentrations ( spikes ). Characterizing the distribution of laboratory control samples (at minimum, variability and mean) is necessary to develop limits for (a) background track densities and (b) RPE of laboratory QC samples. Laboratory QC samples are designed to: (a) measure and track variability within the entire laboratory’s quality system , and (b) document the degree of agreement to concentrations in a STAR . Laboratory QC samples shall be taken from different sheets of alpha-sensitive material to measure the variability of material and analysis system responses within and between batches . 10.5.3 ATD Laboratory—Laboratory Duplicates or Recounts Note—As a best practice, laboratory duplicates and recounts can provide estimates of imprecision in different portions of the lab processes. Recounts of the same detector area assess analysis system variability and are often conducted as part of investigations after failed QC checks. As with other QC checks, continued performance within limits provides evidence of the limited imprecision caused by laboratory handling.