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10 October 2008

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

Category: Instrumentation and Measurements — Instrument Calibration (IC)

The following question was answered by an expert in the appropriate field:

I noticed that standard ANSI/HPS N13.49-2001 recommends that the source(s) used to calibrate radiation-detection instruments be traceable to a national standards lab (NIST). Should the source(s) be recertified at any specified periodicity? If there is some recommended recertification periodicity, is it dependent upon the type of source and/or uses of the source?

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

Answer posted on 15 September 2003. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.