depth profiling with detectors

["Minnema, Douglas" <Douglas.Minnema@nnsa.doe.gov>]

Phil and all,



Many years ago in a former life, I was looking at these techniques during

the establishment of the UMTRA program (circa 1980).  I spent a lot of time

on the Grand Junctions mill tailings pile and others playing with

instrumentation, and also worked with the calibration models you mentioned.

I had two basic problems at the time, but have been long removed from the

program, so I don't know if either was addressed.



First, at the time they were using a deconvolution technique to correct the

raw logging data to improve the estimate of the spatial distribution of the

results.  This technique had been developed for hard rock well-logging

during the days when the US was evaluating the available uranium resources.

My studies indicated that these deconvolution algorithms were very sensitive

to the statistical fluctuations of the data, which were especially

problemmatic when dealing with small signal-to-noise ratios.



Second, I had a great deal of difficulty finding a method of establishing a

borehole in loose soil.  We tried multiple techniques for casing a hole, and

then after sampling we trenched around the casing and took soil samples for

comparison.  No matter which way we used, we always cross-contaminated the

hole to the point where the results were not really characteristic of the

situation.



As these things often go, the project was taken over by another group before

I could come to resolution on these issues, although I had conveyed to them

my observations.  I am curious as to how these concerns are dealt with

today.



Thanks,



Doug Minnema, PhD, CHP

National Nuclear Security Administration, US DOE

<Douglas.Minnema@nnsa.doe.gov>



-----Original Message-----

From: Philip Egidi [mailto:phil.egidi@state.co.us]

Sent: Monday, June 03, 2002 12:35 PM



There was a protocol developed using downhole 2 x2 NaI detectors for

estimating depth of contamination on UMTRA sites.  Total counts using a

scaler were converted to equivalent radium in soil.  It was used on

thousands of properties in Grand Junction, and on uranium mill cleanups.

 Results varied, most data was fairly representative, but sometimes

underestimated by as much as a factor of 3 (volume of material needed to

be excavated).  The now-defunct Technical Measurements Center at the DOE

facility in Grand Junction published protocols for calibrating the

instruments using the borehole models they had there on-site that

accounted for moisture, self attenuation, etc.  The methodology has a

practical application in the field, recognizing that heterogeneity is a

big factor (the data is only representative of a discrete area of

course).



Phil Egidi

phil.egidi@state.co.us 





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