Re: start up calibration facility

[avest@magnus.acs.ohio-state.edu (Albert Lee Vest)]

>I'm looking for recommendations and information on starting up
>a calibration facility for portable detectors here at the
>University of Maryland.  The RSO here about 10 years ago used to
>calibrate their own detectors using a Cs-137 source with an attached
>sliding Attenuator from J L SHEPHERD, out of Glendale, CA.
>I have seen smaller versions for around 3500 dollars, and we
>have a pulser for cpm meters;  however I have no experience in
>setting up or calibrating other than what I have read in a text.

Steve,

If I were in your shoes?
Keep the Shepherd source.  It's going to remain useful for many years to 
come.  Make sure the distance range is updated for decay periodically, and 
that it's long enough for near-background ranges of instruments.  Our lab is 
a bit cramped; we have a Bicron Micro-Rem(TM) meter, and we just have to 
guess for the lowest scale, which goes from "0" to 20 microrem/hr, because 
our range isn't long enough.  (It's pretty narrow, too; if they're assigning 
you new space for this start-up facility, be sure to ask for a range wide 
enough to minimize scattering from the walls)  The new 100 mrem/year dose 
limit makes low-range accuracy important.

Also be aware of regulatory requirements:  The results of all RADIATION 
measurements are to be recorded in DOSE or DOSE EQUIVALENT units.  So when 
setting up the range, make sure to use the *rem* gamma constant, not the 
*Roentgen* gamma constant we all know and love. The results of all 
CONTAMINATION measurements have to be in ACTIVITY units (not CPM and not 
mrem/hr) like microcuries or DPM.  Since most of our instrument users frisk 
their labs, and themselves, for contamination, and your university is likely 
to be similar, I think this kind of calibration is more important than using 
the Cs-137 range:  Make sure you have a good supply of point-like sources 
and wide-area sources of long-lived analogs of the nuclides used by the 
instrument's main users.  Use these sources to give the users conversion 
factors from meter response (cpm, cps, etc.) to DPM and/or DPM/100cmcm for 
the nuclides they use.  A standard probe-surface distance, for this 
efficiency, is 1 cm.

By all means get a copy of NCRP-112, too.  We're still waiting for ours.>:-|
Albert Lee Vest    avest@magnus.acs.ohio-state.edu
health physicist        Office of Radiation Safety
(614)292-0122            The Ohio State University
--All standard and nonstandard disclaimers apply--