This message may not have made it out to the net. My apologies if this
is a repeat message.
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