Re[5]: 137Cs check sources -Reply

[TDC@ehssun.lbl.gov]

VERY old instruments would read zero.

The problem is solved because proper technique is to have the meter on
while going from a low area to a higher area.

Except under very special circumstances as you go from low to high as it
starts to get anywhere near that 100 mR/hr range - you stop going!  There's
a problem, you don't need to be there under those circumstances, get out.

If you are already in the area and it goes to 100 mR/hr - get out NOW!  If
it read higher you couldn't get out any faster.

SO - it gives you all the information you need to know from a "survey"
instrument - the area is higher than you want to be in - so get out.  The
purpose of such an instrument is NOT dosimetry.

The advantage of GM over IC is that GMs tend to be more rugged and
durable and less susceptable to other influences.  So - for a group used
instrument - which usually aren't handled with the greatest of care - there
is a greater probability it is working!

Anyhow - I didn't intend to get into the discussion of the appropriate
instrument for the area - I simply wanted to point out that the "zero
reading in a high field from a GM" is NOT a characteristic of the GM tube -
but the support circuitry and that this has be determined and fixed.

Ted de Castro
tdc@ehssun.lbl.gov
University of California Lawrence Berkeley Laboratory
Bldg 75B Rm 112A
Berkeley, CA 94720
(510) 486-5256
(510) 486-7207 - FAX

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