INSTRUMENT CALIBRATION

["Fleming, Kenneth" <knflemin@bechtel.com>]

I recently had a peer come up and ask a question regarding calibration of
portable instruments.  A debate began over whether portable instruments
could be "calibrated" outside of a laboratory environment (e.g., in the
field).  We've all had the opportunity in the past or present of conducting
source checks and "calibrating" instruments in areas that would most
definitely not be considered to be a lab.  ANSI N323A-1997 defines several
terms:  calibrate, national standard, secondary standard, and tertiary
standard.  The standard provides good information in Section 4 about
calibration.

The questions I'm providing are how legitimate is it to conduct "field
calibrations" (typically using one source at on one range) and use the
subsequent efficiency to determine activity?  (This instrument may have been
calibrated by the manufacturer/vendor to a different source and then field
calibrated.)  If it is legitimate to calibrate in the field, is it necessary
to send instruments to manufacturers or other calibration vendors to be
calibrated, we can still calibrate in the field on an annual basis?  From my
read on calibration and a discussion with the ANSI N323A working group
chair, a calibration must take place in a location that maintains at a
minimum NIST traceable, tertiary standards and these standards need to be
part of a managed QA program which are sent off routinely (say once a year)
to be verified.

Also at issue was the interchangeability of separate detectors onto a
ratemeter.  This subject is discussed in the Standard.  Probes are allowed
to be changed without recalibration if the variation between the new and
previous baseline reading is within 20%.  The calibrated efficiency (from
the manufacturer) is intended to remain the same unless you can show that
the standards used to calibrate are part of QA program.  This may be news to
many field hounds, but this is message I was given. 

Obviously, I'm more concerned operationally about survey technique because
this in itself is the largest variable in a survey.  I'd be interested in
how others view this subject regarding calibration.  If there are any
regulators (either DOE, NRC, or Agreement State) looking at this I'd much
appreciate how you would view this if you came upon a site where
efficiencies changed on a daily basis.  With this I'll call it a week and
await any responses.

This message is most definitely mine alone.


Kenny Fleming CHP CSP
FUSRAP Radiological Control Supervisor
knflemin@bechtel.com
(423) 220-2306
(423) 220-2464 FAX

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