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RE: Cs-137 and Pu-239+240
Paul:
You are correct about being careful about assigning ratios for Cs-137 to
Pu-239. It is possible to identify sources of local contamination based on
ratios but it takes a lot of care. At the INEL we did exhaustive studies
of background and sources. Near two sources we clearly established
differences in ratios based on the source. One source was dominated by
Sr-90 and the other by Cs-137. Near the sources the ratios to Pu were
greatly different from the background ratios. The ratios approached
background ratios with distance. In these cases, the ratios did not add
information. The concentration with distance was the best indicator of
source (we had lots of samples). The variation between samples when using
ratios should also give one pause to consider this technique to identify a
source.
Another problem is sample depth. The concentration profile of the
different radionuclides in the soil are dependent upon their chemical
characteristics in the soil. The ratios will be different between the 0-5
cm depth and the 5-10 cm depth. The ratios also change with time.
Soil type and precipitation are also major problems. The concentration
profiles are highly dependent upon these two factors. The Cs-137 to Sr-90
profile in Florida (sandy soil, little humus) is markedly different from
the rest of the USA. The Cs-137 to Sr-90 to Pu concentration profiles at
one location in Alaska where the precipitation was less than 10 in/y was
very different from a location that had 60 in/y with similar soil types.
If you need references for all this, none was published in the open
literature, but exist in DOE reports in a box somewhere.
DOE EML publishes measurements made world-wide and should be of use for
showing the problems and if need be establishing an AVERAGE ratio.
The real answer is: Take a lot of measurements.
Joe Alvarez
Auxier & Associates, Inc.
10317 Technology Dr., Suite 1
Knoxville, TN 37932
jalvarez@auxier.com
Tel: 423-675-3669
FAX: 423-675-3677
Joe Alvarez
Auxier & Associates, Inc.
10317 Technology Dr., Suite 1
Knoxville, TN 37932
jalvarez@auxier.com
Tel: 423-675-3669
FAX: 423-675-3677
-----Original Message-----
From: Charp, Paul [SMTP:pac4@cdc.gov]
Sent: Wednesday, September 23, 1998 3:43 PM
To: Multiple recipients of list
Subject: Cs-137 and Pu-239+240
Radsafers:
I am having some interesting conversations (arguments?) over the importance
or relevance of Cs-137/Pu-239+240 ratios in soils. At this point in time,
I
am not too comfortable in naming the site or the state. However, we are
collecting samples for Pu analyses but Cs was not included in the sampling
plan. The state health department believes that the Cs ratio is important
in determining the source of Pu. In my reviews of environmental data from
different locations, there does not appear to be any uniform value for the
Cs/Pu ratio. The questions I have are: 1) is there a benefit for
calculating these ratios, especially since the data for the site in
question
does not yet exist; 2) how important is the soil type given the fact that
Cs
and Pu have different chemical characteristics and; 3) is there an accepted
Cs/Pu ratio for environmental samples, especially those samples near
background values?
thanks --
Paul Charp (pac4@cdc.gov)
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