[ RadSafe ] Matching Backgrounds for Gamma Count Rates

[Minnema, Douglas]

Phil and all,

I led a team that used this approach a few years ago in a study of a
beryllium (Be) contaminated building (fascinating study, but too long a
story to tell here).  We had cut 1-m^2 sections out of the carpets and beat
the dirt out in a plastic bag, then sent the dirt off for bulk analysis of
Be.  Knowing the bulk amount of Be, the mass of the dirt sample, and the
area of the carpet piece, we could convert the results into standard
contamination level units, which for Be are microgram per 100 cm^2.
Plotting the results in the manner described below allowed us to understand
very well what the background was and where the contamination was, since we
had no standard way of assessing background.  In the end we had sampled
about 180,000 ft^2 of buildings.

The process worked great, and seemed like old hand to the two of us on the
team that were HP's.  Interesting, though, the IH's on the team really
struggled with the concept.  (Not a critique of the individuals, only an
observation of fact since the method received much debate among the IH's who
looked at the results).  Good old RadCon math came to the rescue once more.

Doug Minnema, PhD, CHP
National Nuclear Security Administration, US DOE

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl]On
Behalf Of Philip Egidi
Sent: Thursday, August 18, 2005 11:11 AM
To: luke.mccormick at dhs.gov; radsafe at radlab.nl
Subject: Re:[ RadSafe ] Matching Backgrounds for Gamma Count Rates


I agree with Luke, and also offer another approach.

Make your measurements in the areas you think are not contaminated
based on the historical site assessment, process knowledge, and
experience.
Try to do them with data loggers such that you have data to dump into a
spreadsheet.  Do a cumulative probability plot and look for the knee, if
there is one.
That should give you a representation of ambient gamma exposure rates,
and what is atypical.  You can then determine what your upper acceptable
limit for background is graphically, which communicates well to
regulators and the public.
You also need to state that ambient and background are the same for the
purposes you are using them for.



Phil Egidi
EPS III
Radiation Management Unit
Compliance Program
Hazardous Materials and Waste Management Division
CDPHE
(303)692-3447
(303)759-5355 (fax)



If electricity comes from electrons, does morality come from morons?

>>> "Mccormick, Luke I" <luke.mccormick at dhs.gov> 08/18/05 07:42AM >>>




With clearance values as stupidly low as they are, most of the time
you
need to take a background measurement. Only at one spot have I found
the
entire building crapped up. There is usually at least 1 room you can
get a
reasonable bkgd from. Yes, true bkgd will vary room to room but as long
as
you are using the MARSSIM methodology you can get by. Remember for
clearance purposes, background is the upper 95% confidence limit value
of
what you measured, not the mean value. If you use the mean you have
just
assumed 50% of your measurements are above background.

____________________Reply Separator____________________
Subject:    [ RadSafe ] Matching Backgrounds for Gamma Count Rates
Author:     radsafe-bounces at radlab.nl 
Date:       8/18/2005 12:12 AM




       For building or lab closure surveys, I rarely have pre-op gamma
       count rate
       measurements for comparison.  To try and find a "matching"
       location to  obtain
       gamma backgrounds is next to impossible.  As previously
       discussed  here, gamma
       count rates vary widely.  I would be interested in hearing how
       others have
       handled this problem.

       Joel I. Cehn, CHP
       _joelc at alum.wpi.edu_ (mailto:joelc at alum.wpi.edu)

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