Interim Baseline Radiological Investigation Report in
Support of the Upton Rare Earth Processing Plant
November 15, 2012
22
The relationship between the entire data set (n=16) of radium-226 concentrations and gamma
count rates yields a poor correlation coefficient (R
2
= 0.35) with poor residuals (i.e., predicted
minus observed radium-226 concentrations). An iteration in which one of the observations (2.3
pCi g
-1
/15,652 cpm [SS-16-SS-061412]) was omitted from the regression yielded an improved
correlation coefficient (R
2
=0.45) with poor residuals. Average residuals did not exhibit a bias
(indicating a tendency to over- or under-estimate soil radium-226 concentrations).
Table 4.5. Radium-226 Concentrations and Integrated Gamma Count Rates
Sample Location
Radium-226
(pCi g
-1
)
Th-Nat
(pCi g
-1
)
Gamma Count Rate
(cpm)
SS-01-SS-061412
1.4
1.5
13740
SS-02-SS-061412
1.6
2.6
16634
SS-03-SS-061412
1.5
2.0
13336
SS-04-SS-061412
1.5
1.8
14519
SS-05-SS-061412
1.6
2.6
16443
SS-06-SS-061412
1.6
2.9
17727
SS-07-SS-061412
a
1.8
3.0
16553
SS-08-SS-061412
2.3
3.1
17833
SS-09-SS-061412
1.5
1.8
12819
SS-10-SS-061412
a
1.7
3.2
17388
SS-11-SS-061412
1.9
2.2
16259
SS-12-SS-061412
a
1.4
2.4
16056
SS-13-SS-061412
a
1.3
1.4
12147
SS-14-SS-061412
2.2
2.9
17463
SS-15-SS-061412
1.6
2.9
15955
SS-16-SS-061412
2.3
2.2
15652
Notes:
a
Duplicate sample collected at this location. Ra-226 and Th-nat concentrations average for the calculation.
cpm = counts per minute
pCi g
-1
= picocuries per gram
The linear regression model for this iteration, which has the higher correlation coefficient of the
two and was used to estimate radium-226 concentrations from the gamma survey data for the
Upton Project is:
Concentration
Ra-226
= 1*10
-4
x cpm + 0.0221
A stepwise approach was not taken because it was clear, on cursory evaluation of the correlation
plot of all observations, that the data were too few and variable from which to draw salient
trends.
It is important to acknowledge that discrepancies between measured soil radium-226
concentrations reported by the laboratory and corresponding radium-226 concentrations
estimated by gamma surveys are inevitable in a characterization survey of this nature and
