Interim Baseline Radiological Investigation Report
November 14, 2012
Bear Lodge Project, for Rare Element Resources, Ltd.
Rev.1
42
The values determined above are similar to U.S. background concentrations reported in the
United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) Report to
the General Assembly, Sources and Effects of Ionizing Radiation, Annex B (UNSCEAR, 2000).
The regional concentrations reported in this reference document are: uranium-238 (2.4x10
-17
to
1.4x10
-16
µCi/ml), natural thorium (1.9x10
-17
µCi/ml based on an average of thorium-228 and
thorium-232 regional concentrations), thorium-230 (1.6x10
-17
µCi/ml), and radium-226 (1.6x10
-
17
µCi/ml).
The ranges of airborne radioactive particulate concentrations were the following percentages of
their respective 10 CFR 20 Appendix B effluent concentrations:
•
Natural uranium: 0.000 to 0.006 percent.
•
Natural thorium: 0.001 to 0.084 percent.
•
Thorium-230: 0.000 to 0.008 percent.
•
Radium-226: 0.000 to 0.025 percent.
In no cases were the LLDs higher that their respective 10 CFR 20 effluent concentration limits.
8.1.2 Lanthanide Particulates
Table 8.4 presents the concentrations of lanthanides in sample filters and in air. Table 8.5 lists
summary statistics for the lanthanides.
Site-wide cerium and lanthanum particulate concentrations in air are 1.2x10
-3
and 6.5x10
-4
µg/m
3
, respectively. In the current set of data, lanthanum concentrations are an order of
magnitude lower than those of cerium. The range of cerium concentrations is 1.2x10
-4
to 2.0x10
-2
µg/m
3
. The range of lanthanum concentrations is 5.9x10
-5
to 1.2x10
-2
µg/m
3
.
