Re: 2X Background Reference

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

>I have seen references to 2X background used for screening purposes,
>but would suggest that not be used as a clean-up criteria.  Background
>(that sea of deadly radiation we live in) becomes a very flighty term

In any discussion, it's good to distinguish which "background" one is
concerned with - the "background" reading of a particular screening
instrument, or the natural EDE "background" received by real or hypothetical
individuals.  From the bulk of your message, youre subject seems to be the
former.

>cleanup goal.  unfortunately, the fill soil for reconstruction
>was required to be 'background'.  Since, for an average of samples,
>1/2 will be below the mean and 1/2 will be above the mean,  the fill
>requirement to be at 'background' (defined as the mean background)
>eliminated half of the soils in the area. Since fill could not be
>obtained that would reliably be 'background', we were literally in a hole.

Any time 'background' is interpreted as 'causing the instrument to read at
or below its background level', you're in that hole.  That's why it makes
more sense to interpret (if the rules allow) 'background' as
'indistinguishable from background', and you have quoted a reasonable
criterion of indistinguishability below:

>Lesson learned. Specify background, in particular, soils with 
>concentrations below the upper 95.5% confidence limit (2*sigma)
>will be considered at background.

What I take that to mean is, 'soils for which a screening measurement below
the upper 95.5% confidence limit (2*sigma) is obtained will be considered at
background.'

My opinion on the matter is that using 'background' in any form as a
screening criterion is first cousin to demonstrating that the amount (of
radiation, or of activity) present is 'zero'.  Neither is a policy I would
deliberately choose.

Albert Lee Vest           The Ohio State University
Health Physicist    Room 103 1314 Kinnear Road Bldg
(614)292-1284                     1314 Kinnear Road
avest@magnus.acs.ohio-state.edu   Columbus OH 43212
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