Answer to Question #10937 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Instrument Calibration (IC)

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

Q

Is there an American National Standards Institute/International Organization for Standardization (ANSI/ISO) standard that limits the size of repairs to a Mylar window on a 100 cm2 probe face?

A

I am not familiar with any ANSI/ISO standard that gives specific guidance as to the size of repairs that are acceptable for Mylar windows used on radiation detectors. It is quite possible that some discussion might be included in some standard, but I cannot identify any particular reference.

To my knowledge, there is no dictate against repairing or replacing a detector window. What is required, however, by many regulating, recommending, and standard-setting groups is that instruments to be used must be properly calibrated at regular intervals. An associated requirement is that whenever any repairs are done or other actions taken that might affect the response characteristics of the instrument in question, the instrument should be recalibrated to ensure proper response.

Changing a window or repairing a window has the potential to result in an alteration of the window thickness and other possible changes that could result from inadvertent errors during the repair that, in my opinion, could produce a change in instrument response, and recalibration would be appropriate. Such recalibration considerations are mentioned, for example, in National Council on Radiation Protection and Measurements (NCRP) Report No. 112, Calibration of Survey Instruments Used in Radiation Protection for the Assessment of Ionizing Radiation Fields and Radioactive Surface Contamination, (NCRP, 1991, paragraphs 2.8, 4.6, 5.6, 6.6, and 7.6).

George Chabot, PhD

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