help

["Michael R. Dupray" <MRDupray@lbl.gov>]

Al Smith wrote:



It is rule-of-thumbish to take the following viewpoint.

Do not be concerned when the rate in the "boxed-in"

space is less than double the rate over an open space.

The underlying principle here is that you go from a 2-pi

geometry (open space) to a 4-pi geometry where the higher

rate is observed.  (Support this argument with vigorous arm-waving or a 

cold stare.)



In the above it is assumed the concrete is uniform in

radioactivity at all places of interest.  Typical Bay Area

concretes contain up to 1 pci/gram of U-238, up to 1 pci/gram

of Th-232, and up to 10 pCi/gram of potassium.  Many contain

less, but the ratios among the three tend to be constant.

If Jay's equipment has spectroscopy capability, even with NaI,

then a reasonable test is to check carefully whether spectra

in the two different geometries look different.  Any significant

contaminant (man-added) should at least show up as a lump on a

peak or a bump somewhere along the continuum.  The next strategy

would be to core or jack-hammer samples from the two places

and do Lab gamma-spectroscopy - - I suppose we could even do

that in a pinch.



I don't know of modelling studies that apply to this sort of

dilemma, although I suspect such do exist.  Personally, I go the

spectroscopy route in cases like this - - results against which

no argument stands a chance.





Al Smith



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