Re: Frequency of SRD Calibration

[Bob Flood <bflood@SLAC.Stanford.EDU>]

At 08:57 AM 12/19/96 -0600, you wrote:
>     Two HPs at my site disagree on whether or not our Self Reading 
>     Dosimeters (SRDs) should be treated as primary dosimeters...

First of all, the use of two primary dosimeters is a project for the
Department of Redundancy Department. Primary and secondary dosimeters serve
different purposes, the primary dosimeter being designed to determine dose
of record and the secondary providing real-time dose estimates for
on-the-job exposure control. The secondary dosimeter can also serves as a
backup in case of failure of the primary dosimeter, but this is an extra
added attraction, not the primary function of the dosimeter, hence the term
"seconday."

SRDs provide lots of small dose measurements that must be recorded and
tracked if a meaningful cumulative dose estimate is expected. In that
light, the effectiveness of the recording and tracking system at capturing
all SRD data and  the accuracy of the data entry (reading and
transcription) far outweigh the measurement accuracy issues in influencing
the dose totals. In general, the dose total from SRD data at the end of a
monitoring period is more a function of the effectiveness of the tracking
system than the measurement accuracy of the device. Thus, a longer
calibration interval is reasonable for a secondary dosimeter.

Having said that, there is a simple practice that adds a measure of
validity to a SRD total (defensive dosimetry again) in case of a future
challenge: if person's primary dosimeter is lost or damaged so that a
reading cannot be obtained, test that person's SRD by irradiating and
reading it, and recording the data in the dose investigation. A routine
calibration before use and a test after use showing acceptable performance
will go a long way toward stopping arguments about the dose total.


Bob Flood
Stanford Linear Accelerator Center
(415) 926-3793     bflood@slac.stanford.edu
Unless otherwise noted, all opinions are mine alone.