Interim Baseline Radiological Investigation Report in
Support of the Upton Rare Earth Processing Plant
November 15, 2012
7
3.0
GPS-BASED GAMMA (DIRECT RADIATION) SURVEY
This section documents the results of the baseline gamma radiation survey of the Upton Project
conducted in June 2012. The findings discussed in this section are reflected largely in the
supporting figures; the text is limited to a discussion of trends and salient findings.
3.1 GPS Survey Methods
A GPS-based gamma survey was conducted at the Upton Project on three days, between June 11
and 13, 2012. The detection systems were unshielded 2-in. by 2-in. sodium iodide detectors
(Ludlum Model 44-10), each of which was coupled to a ratemeter/scaler (Ludlum Model 2221,
set in ratemeter mode) and, in turn, a Trimble Pro XRS GPS Receiver with Trimble TSCe
Datalogger. Scanning was performed on north-south transects spaced at 100 m, at a speed less
than 1.5 m s
-1
with differentially corrected x- and y-coordinates and gamma count rates recorded
every second. The survey was conducted on foot while carrying the requisite equipment in
backpacks. The detectors were held at approximately 0.5 m above ground surface in the walking
survey.
The survey instruments were in calibration and function checked daily, before and after use.
Calibration and function forms are provided in Appendix A.
3.2 Results of GPS-Based Gamma Survey
Data presented in the following sections indicate that the distribution of the Upton Project
gamma count rates is non-parametric. The data also indicate two statistically distinct populations.
The data are first summarized collectively.
The gamma count rates were converted into exposure rates, using the method and linear
correlations described in Section 3.3. The gamma count rates are displayed as exposure rates in
Figure 3.3. All of the statistical analyses and summaries presented henceforth, including the
illustrations, were developed using Minitab 15: a statistical software.
