I've been following the discussion of the source checking of instruments with some interest. There are a couple of key points that are relevant to the issue :
1 ) Sources used to calibrate the instrument need to be similar in emissions to the radiation the instrument will be used to measure in the field.
2 ) Sources used for calibration must be characterized to national standards.
3 ) When CALIBRATING the instrument, the range and linearity should be checked to ensure required accuracy and function on all of the scales allowed for use.
4 ) Check sources need not be characterized, but they should have relatively stable and well known features.
- Decay of check sources may need to be factored in to response check criteria.
- If the isotopic mix of the check source is changing due to build in ( as may be possible from some processed, natural source material )then your reading may change in unexpected manners.
- The instrument should be source checked on each range that is used. ( there are solder joints resistors etc. on range switches that have been known to fail )
5 ) A response check is different from a source check. A response check merely checks to see that the instrument indicates the presence of radiation on at least one scale and is not looking for a specific value. These type of periodic check is required for some emergency response instruments.
I think that this is basically a summary of some of the portable instrument standard criteria. It would seem to me that it would be very easy to justify the use of response check of instruments with lantern mantles. I think that a little more effort may be required if you desire to use a lantern mantle for a check source. The biggest variable that I see is the age related isotopic mix that may be present from batch to batch and from vendor to vendor.
... very clearly, mine and mine alone ...
Ron LaVera
lavera.r@nypa.gov
-----Original Message-----
From: Daren Perrero [mailto:dmperrero@email.msn.com]
Sent: Monday, September 21, 1998 6:35 PM
To: Multiple recipients of list
Subject: RE: Lantern mantles
Dave, the use of the check source certainly provides a reasonable assurance
that the meter is responding to radiation in a consistent manner, but can
you make any assumptions regarding the instrument's linearity or accuracy
over its range of operation from a single check point? I thought that the
necessity of an periodic (full) calibration was done for this reason, among
others.
Daren Perrero
dmperrero@email.msn.com
I'm with the government, I'm here to help you....
> -----Original Message-----
> From: radsafe@romulus.ehs.uiuc.edu
> [mailto:radsafe@romulus.ehs.uiuc.edu]On Behalf Of David Krueger
> Sent: Monday, September 21, 1998 12:23 PM
> To: Multiple recipients of list
> Subject: Re: Lantern mantles
>
> My response is that a check source only need to be long lived so that its
> radioactivity is not going to change over the period that it will be used.
> If an instrument is properly calibrated with traceable sources and its
> response to any check source (traceable or not) is documented, then
> continuing to use that source to verify that the instrument
> responds in the
> same way (gives the same reading consistantly) would appear to be all that
> is necessary. Otherwise, Mike's suggestion basically ends up calibrating
> the instrument every time it is used.
>
> Dave Krueger, CHP
> dkrueger@icnpharm.com
>
>
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