Answer to Question #533 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Instrument Calibration (IC)

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

How is the minimum detection efficiency of an NaI detector used to detect gamma energies in the low range 60 keV to 300 keV calculated?

Detection efficiency is dependent on a number of factors and cannot be calculated without empirical data. As such, I would suggest that a series of measurements be performed using the system that you have an interest with or that you contact the manufacturer. It may be that, due to a difficulty with translation, the question could have been—"How do I calculate the minimum detectable activity of an NaI detector used for detecting gamma rays in the energy range from 60 keV up to 300 keV?" If so, I recommend that you download Chapter 6 from the MARSSIM manual at the EPA Obtain a Copy of Marssim Web page. You will only need Chapter 6 and it isn't very large. It contains a fairly lengthy discussion of this topic and includes a number of formulae.

Bobby Coleman
Oak Ridge National Laboratory

Answer posted on 29 December 2000. 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.