Activity determination in boxes containing DU

["William F Miller/MILLERWF/CC01/INEEL/US" <MILLERWF@INEL.GOV>]

I need advice/suggestions on how to determine activity in large packages

containing materials contaminated with DU.

The contaminated material is general construction waste from a

contamination area, stuff  like conduit, breaker boxes, metal supports,

insulation, wood, Lexan, etc.

Right now I calculate activity by utilizing the MicroShield program and the

averaging the direct rad readings from the accessible sides.  These direct

rad readings are typically in the 20 microR range.

Using MicroShield I build a container of the same size and shape.  I then

calculate a source material density by dividing the net weight by the net

volume of the package.  The source is the U-238 and the Pa-234, Th-234

daughters and their concentration (uCi/cc) is a standard value I picked out

of the air - 0.04.  I include the photons below 0.015

After the run MicroSheild provides an exposure rate with buildup.

I determine the ratio between the actual readings and the MicroShield

value, then multiply the concentration (0.04) by that ratio to arrive at an

activity in the actual package.

I'm concerned about the error that this method probably has.  The density

of the source is effected by the air gaps in the package and by the mixture

of the contaminated materials (wood vs. metal).  I also have to guess at a

material 'type' to assign as the source material (wood vs. iron vs. water

vs. cellulose).

There is also the issue of the low photon incidence associated with DU.

There is a 1.1 MeV gamma from Pa-234 but it only occurs 0.6% of the time.

Does anyone else have to deal with this type problem?  How would someone

determine activity in packages containing Pu-239 contaminated material?

I would prefer an open discussion on the list but my personal email is

millerwf@inel.gov

Thanks

Bill Miller

INEEL

208-526-2185



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