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29 August 2008

Answer to Question #1238 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Instrument Calibration (IC)

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

A dose calibrator linearity test can be done using the shield method (CaliCheck kit). I found that the results are frequently not reliable: 5% criteria was exceeded even if it was done in 3 minutes and the dose calibrator was functioning. How can one reduce possible errors or variability?

I have this question submitted to a representative of a major dose calibrator manufacturer and I will update this answer when additional information is obtained. However, in that these instruments are most often well-type ionization chambers with sensitive electrometer circuits, they are limited in the sense that there is no gas multiplication when the gamma ray interacts with the chamber wall or directly with the gas. Thus to increase the measured current, especially with a shielded vial for ⁹⁹Mo breakthrough or an activity linearity test, you might try using a large quantity of radioactivity. Do check with the manufacturer's instrument manual, or contact the manufacturer directly, as there may be a problem with the equipment. David J. Allard, CHP

Answer posted on 5 November 2001. 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.