Re:GM Counters in High Backgrounds

[Rodney Bauman <rodney_bauman@wssrap-host.wssrap.com>]

I used to have some of the same arguments with the house and contract RTs. 
However, our arguments usually centered around dose rates (e.g., RO-2 readings)
instead of count rates.  The techs would always argue that a net reading would
increase if counted/surveyed in a lower background area.  That is, the high
background levels "hid" most of the net activity which would only become
apparent once counted/surveyed in a low background area.

However, the fact is that net activity is net activity.  High background rates
will inevitably increase your background variance and, coupled with the high
background rate, increase your background decision level; which, in turn, will
increase your net activity MDA.  Based on the location's background variance,
the measuring of 500 net cpm activity may not be possible to a high level of
confidence - and that may be the problem.  But if possible, then 1500 gross cpm
in a 1000 cpm background should produce approximately 550 gross cpm in a 50 cpm
background.

Rodney Bauman, CHP, RRPT
rodney_bauman@wssrap-host.wssrap.com

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