Performance-Specifications-for-Instrumentation-Systems

MS-PC 2015: Performance Specifications for Instrumentation Systems Designed to Measure Radon Gas in Air Page 6 of 20 4 Definitions & Abbreviations Continued Standard Test Atmosphere for Radon (STAR) – A standard test atmosphere for radon (often called a “radon chamber”), sufficient in size and configuration, radon concentration range, and radon concentration controls such that: 1. At least five simultaneous and independent measurements of radon concentration can be conducted at the high and/or low limits of the ranges of radon concentration (e.g., in pCi/L) or integrated concentration (e.g., in pCi-d/L), during which time the conditions in the STAR are as constant as practicable; 2. the performance of the devices being tested is their function for measuring radon concentration; 3. temperature, relative humidity and radon concentration are recorded hourly or more frequently by devices with annual NIST-traceable calibrations (or traceable as defined below) and documented uncertainty estimates; 4. barometric pressure in the STAR at local conditions is recorded or otherwise available and included in exposure reports; 5. temperature and relative humidity are controlled to within the limits of this standard for the particular test being conducted; 6. the uncertainty of the average radon concentration during the exposure period is calculated using methods recommended by NIST (NIST TN-1297), published and reported with each exposure; 7. the STAR is operated under a documented quality management system consistent with recognized international standards such as ISO 9001. Thoron – the specific isotope radon-220. Traceable – For the purpose of this standard, the response of an instrument or system can be related, or traced, with an unbroken chain of documentation and associated estimates of uncertainty, to a standard maintained by NIST. Radon concentration traceability requires that the radon concentration used as a working standard was derived from a certified NIST radium-226 standard. Note: These working standards of radon are usually constructed by bubbling nitrogen, aged air or other gas through a vessel containing a certified radium solution (Ra-226 in weak acid). By strict definition, any sealed ampoule that was purchased from NIST and that is opened is no longer NIST-traceable. With careful handling, however, such a solution can be transferred to another vessel while retaining its quality. At present, NIST produces Standard Reference Material (SRM) Ra-226 solutions that may be used to produce working laboratory standards for radon. There is no SRM for radon. General procedures for producing these working standards are described by the National Council on Radiation Protection and Measurements (NCRP; see NCRP 1988) and others (e.g., Sensintaffar 1990). Traceability for radon may be achieved through interlaboratory comparisons with a facility using standards as described above.