-3-
(5)
Other factclrs that might account for low or variable IMP readings
are attenuation
conditions
at time of IMP readings were, apparently,
Both wet and dry weights
conditions
not recorded.
of soil samples are taken, but moisture
on the islands change from day to day, and soil samples
are not taken in conjunction
expressed
Soil moisture
due to soil moisture or soil density.
with most IMP readings.
John Tipton
the opinion that IMP errors due to soil moisture and
density would be on the order of 10 to 15%.
(6)
The IMP is calibrated
Am source
in the field three times a day using a known
(100 mCi*3%)
through a 180° arc.
suspended under the IMP detector and moved
The detector has a lead and cadmium shield
at an angle of 50° from the verticle.
The iMP calibration assumes
a soil density of 1.5 g/cm3.
(7)
The IMP has never been calibrated
in the soil.
done.
against a known
no pads available with 241Am NBS
standard sources for field calibration.
(8)
Am concentration
Everyone present seemed to agree that this should be
There are, apparently,
extensive
241
Experiments
involving
soil sampling would be necessary.
Depth control on surface soil samples appears to be rather “sloppy”
(my term).
A cookie cutter designed to control depth has not been
used since sometime
in the period October-December.
is to scoc)p from soil surface.
Present procedure
Only the top “3 cm” surface soil
samples are used for cleanup calculations.
Samples at 10 and 20 cm
depths have been taken at each surface sample location, but only
to indicate whether
profiles to greater depths are required.
(On
May 3, 1978, M. Barnes informed me these 10 and 20 cm samples are
no longer being taken, on orders from Bruce Church.
the collection
at those depths. )
analyzed by wet chemistry,
He also initiated
The 10 and 20 cm samples are
but utility of data is decreased by the
fact that soil from upper layers has sometimes fallen to lower cut
levels during sampling operation.
Apparently,
these 10 and 20 cm
cuts are the only profile data that may in some sense be labeled as
representative.
The profile data supplied to the Advisory Group for
the April 26 and 27, 1978, meeting in Denver, CO, were taken in areas