Answer to Question #2452 Submitted to "Ask the Experts"

Q

Is there a reference document that states a requirement for the length of time background measurements are to be made for a gamma spectroscopy system? In a recent audit I was informed that for statistical purposes it was necessary to run the weekly background for 1,000 minutes.

A

You're obviously looking for certain minimum detectable activity levels and want a good handle on background. I'm not aware of any "requirement" for a weekly 1,000-minute check on background for gamma spectroscopy. This sounds like a significant period of the available counting time in a seven-day week. Depending on sample workload it should be possible to do this 1,000-minute count over a weekend, setting up to run at the end of the day on Friday. Once you have documented a stable background on a particular system, it would not be unreasonable to do monthly or quarterly 1,000-minute background counts, with shorter-duration weekly quality-control background checks. I'd check your background control charts for stability, look at the government protocols referenced in this topical area of ATE, and contact other gamma-counting labs. If you need contacts, let me know.

David J. Allard, CHP