Occupational Dose Evaluation in Support of the Development of
October, 2012
Rare Element Resources, Inc. Bear Lodge Project
3
1.2
Report Objective
The purpose of this report is to identify potential human exposure pathways to naturally
occurring radioactivity associated with mining and processing of the Bear Lodge ore and to
provide a conservative estimate of the magnitude of expected radiation doses to workers
resulting from the proposed actions at the BLP. It includes a perspective on the significance of
this estimate.
NORM --in ore and ore concentrates-- poses potential risks to workers because it emits and/or
contains ionizing radiation. The predominant pathways by which a worker can receive doses
from the ionizing radiation are inhalation and/or inadvertent ingestion of NORM in dust and
exposure to radon gas. Doses from gamma radiation from sources external to the body are also a
potential pathway. To help put these potential exposures in context, regulations applicable to
radioactive materials and potentially relevant to NORM are discussed. A regulatory basis for the
development of an occupational radiation protection program (RPP) is also provided.
1.3
Naturally Occurring Sources of Radiation and Radioactivity
A brief overview and description of important radiological terms is provided in this section to
assist readers who may be unfamiliar with the concepts of natural radiation and radioactivity.
1.3.1
Types of Ionizing Radiation
This report addresses occupational doses from ionizing radiation, which is radiation that has
sufficient energy to create ion pairs when interacting with matter. Ultraviolet, infrared, and
microwaves are non-ionizing forms of electromagnetic radiations and not addressed herein.
Henceforth, radiation is meant to include only ionizing forms of radiation.
There are three types of radiation that are important when considering radiation emitted from
naturally occurring radionuclides present in all environmental media, including soil and rocks.
These are alpha, beta and gamma radiation. Alpha radiation is a particle (in the form of a charged
helium atom) emitted from the nucleus of an atom. Alpha radiation interacts with matter quickly
and frequently; therefore, they do not travel far before depositing all their energy. Alpha
radiation is readily stopped by air or a sheet of paper. Beta radiation is a particle (electron)
emitted from the nucleus of an atom that is smaller than alpha radiation and can travel farther in
matter. Beta radiation can be stopped by a few inches of water or by the skin of the body.
Gamma radiation is electromagnetic and more penetrating than alpha or beta radiation. Gamma
radiation can be stopped by dense materials such as concrete, lead, or a sufficient thickness of
soil or rock. Typically, alpha and beta radiation is only a concern if radioactive material is taken
into the body by inhalation or ingestion. Generally, they are not an external (outside the body)
radiation hazard. Higher energy beta particles are an exception to this, because they can deliver a
radiation dose to the skin from an external source. Gamma radiation is a concern from ingestion
and inhalation of radioactive material and external sources.
