DETERMINATION OF THE PLUTONIUM TO AMERICIUM RATIO IN SOIL SAMPLES
FROM ISLAND PEARL
DOE/ERSP TECH NOTENO,2.0
DATED: 12 November 1977
AUTHOR: B.Friesen, DRI
Soil surface samples were collected on Island Pearl in accordance with documented guidelines, The
Samples were analyzed by wet chemistry methods as well as alpha and gamma spectroscopy
techniques in the Eberline Instrument Corp. laboratory and the the results forwarded to DRI. The
objective was to incorporate the Pu/Am ratio into computations required to make estimates of the
Pu distribution on the island based on the 2414m measurements madeby the in situ van (IMP).
Use of the ratio is necessary because direct field measurements cannot be made of plutonium by the
IMP but they can be made of 241 Am which bears a functional relationship to plutonium.
Analysis of the soil sample data involves two steps. First is the determination of a ratio, or if
necessary, a set of ratios that can be used to characterize the Pu to Am relationship. The second is
the determination of the error term(s) associated with the computed ratio(s), The remainder of this
Technical Note will deal with these steps separately.
Determination of one mean ratio for Lujor was made first excluding the 238pu component, then
later
including
238py
along
with
239,240py,
Using
239,240pu
and
241A4m_
laboratory
results, the ratio was determined for each of 10 samples taken from 5 locations on the island, The
arithmetic mean of these 10 numbers was 3.77 with a coefficient of variation of 35.93%.
Some concern was expressed over the magnitude of the spread between lowest and highest ratios;
the range was from 1.78 to 6.00. Simple and weighted mean ratios of 239,240py to
computed for each of 6 arrangements of the data as shown below.
"A" Samples
Ratio No,
1
3
5
7
)
Simple Mean
Weighted Mean
Set or
Subset
Nos. 1-10
1-8
3-8
3-10
241Am were
"B" Samples
Ratio
Ratio No.
1.78
3.10
3.99
3.73
6.00
Ratio
2
4
6
8
10
1.78
4.64
3.80
3.59
5.30
3.72
3.96
3.82
4.00
Weighted
3.98
3.43
3.83
4.36
Mean
Simple
3017
3.30
3.80
4.26
Attention was then directed toward a comparison of surface soil ratios and subsurface ratios taken
at 10 cm and 20 em depths. All tests performed indicated that in the statistical sense all of the
ratios came from the same population, i.e., there was no reason to discard or suspect any of the
numbers, taking them at face value. It was recognized that some outside information not evident in
the data could lead to later changes; however, the decision was made to proceed with available data
for a first approximation. The ratio actually used in preparing the first estimates of 239,240py
for Pearl was 3.825 + .495.
B~2-1