Cs-137 in soil -Reply

[FRAMEP@ORAU.GOV]

Let me add my 2 cents here. As a first approximation, Dale is on target,
typical numbers will be from 0.1 to 1 pCi/g.  

A small point: The stuff is decaying with a 30 year half life, so all other
things being equal, we expect to see today one half of what we saw in
1965.

As a first approximation, we might expect an exponential decrease with
depth for a given soil stratum. As such, you can get very different
results from sampling soil to a depth of 5 cm vs 10 cm at a given location.
The rate of decrease with depth depends on the soil permeabilty among
other things, so what we see in sand can be very different from what
we see in clay even though the same amount of cesium was deposited
on both. Needless to say, the decrease in concentration with depth might
not be exponential because of mixing of the soil ie construction, plowing,
earthworm activity, etc. You can also expect a break in concentrations
going from the A horizon to the B horizon. Here in Oak Ridge, a good
sneeze will blow away the topsoil leaving impermeable clay. This
situation can help keep concentrations in the topsoil high. Another issue
that has already been mentioned is runoff.

Other issues: How well the soil is dried (air drying vs oven) might lead to
a difference of say 10%. Soil density, which can vary, is a factor
because we report activity per gram, not volume. Perhaps even more
important is what we do with the rocks we find in the soil. Keep em and
the Cs-137 concentration goes down, remove em and it goes up. The
point is that the deposition of Cs-137 on a rocky soil results in higher
concentrations than the same deposition on nonrocky soil if the rocks are
discarded (as is usually the case in soil analysis).

Let me give some Oak Ridge numbers (pCi/g) for
0-5 cm/5-10cm/10-15cm /15-20 cm at randomly selected locations (1993)

2/0.16/0.15/0.08
0.9/0.7/0.2/0.09
1.4/0.37/0.07/0.02
5.58/1.06/0.96/0.57
3.6/2.7/1.4/0.5
0.48/0.17/0.16/0.03
1.07/0.137/0.026/0.018
0.6/0.21/0.13/0.03

Some Cs-137 pCi/g numbers from randomly selected  environmental
reports (not Oak Ridge): 0.59,   0.25, 0.88, 0.42, 0.09, 0.54, 

Best of luck Les

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov