Answer to Question #2902 Submitted to "Ask the Experts"

ANSI Standard N13.49-2001 "Performance and Documentation of Radiological Surveys" in section 4.3.1.2 "Other Considerations for Calibration Source Selection" states that the source used for calibration should be traceable to the National Institute of Standards and Technology (NIST). The source manufacturer normally has a standard that has "primary" traceability to NIST in the United States or a national standards organization in another country. The supplier will provide a calibration certification of the source purchased that may subsequently be used for a controlled survey instrument calibration, e.g., a ⁹⁹Tc beta source for calibrating a "pancake" G-M probe for surface contamination. As stated in this ANSI Standard, if the source has a short half-life, it should be decay corrected before used for instrument calibration. However, if the source is handled properly, not damaged in any way where the amount of activity might be lost (e.g., through abrasion), there is no reason to recertify the source. This is especially true for a high-integrity sealed source used for gamma calibration. If you do question the results obtained in an instrument calibration, or if you need an added level of quality assurance due to the critical nature of the measurement, a cross-check to another source or calibrated instrument may be desirable.

David J. Allard, CHP