Cs-137 and Pu-239+240 -Reply

[Duane Schmidt <DWS2@nrc.gov>]

A few years ago, I was involved in work on the historical dose reconstruction project
for residents around the Rocky Flats site, which had released Pu to the environment.
One of the methods that has been used is to look at the ratios of the individual Pu
isotopes (I don't recall off hand the ratios examined). Because the ratios are
expected to be different for material originating at the Rocky Flats site and for
weapons fallout (fissioned), it is possible to determine the origin of the material in
many cases. If you need more details about this approach, let me know.

I also note that Eisenbud (3rd edition) discusses use of a constant ratio of Sr-90 to
Pu in weapons fallout.

Duane.

Duane W. Schmidt, CHP
U.S. Nuclear Regulatory Commission
NMSS/DWM/URB
mailto: dws2@nrc.gov

>>> "Charp, Paul" <pac4@cdc.gov> 09/23/98 03:46pm >>>
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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