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Environmental Radiation

An array of thermoluminescent dosimeters (TLDs) is distributed throughout the Eastern Snake River Plain to monitor for environmental radiation. Beginning in November 2011, the ESER Program also maintains optically stimulated luminescent dosimeters (OSLDs) in the same locations (Figure 13) as the TLDs to run a side-by-side comparison of the two dosimeter technologies. Two OSLDs are in place at each location. TLDs and OSLDs are changed out at the beginning of May and again at the beginning of November after six months in the field. Both sets of dosimeters are currently analyzed by the ISU Environmental Assessment Laboratory.

Thermoluminescent dosimeters were read by the ICP contractor through 2015. In 2016 ISU assumed responsibility for the TLD analysis effort with the transfer of the TLD readers to the ISU radiological sciences laboratory. When the device was operated by the ICP contractor, they employed a proprietary software package that was not transferred to ISU. Idaho State University personnel located commercially available software (WINREMS) and successfully installed it at the end of 2016. They spent most of 2017 developing a set of operational procedures applicable to the WINREMS software. At the time several side by side experimental measurements were made and evaluated to compare TLD results with OSLD results. To accomplish this effort, several TLDs and OSLDs were sent to the DOE Radiological and Environmental Sciences Laboratory (RESL) to be irradiated at predetermined exposures and calibration geometries. The results were evaluated by Dr. Craig Yoder1 and he made four main observations:

  1. The two systems do not measure the same radiological quantity. The TLD system is calibrated to measure the quantity exposure, measured in units of Roentgen. The OSLD system is calibrated to measure the quantity ambient dose equivalent (H*(1)), expressed in units of rem.
  2. The OSLD system measured its intended quantity (i.e., reference irradiation dose) to within 1%.
  3. The TLD system exhibited a negative bias (~11%) for the quantity for which it was calibrated. This calibration bias needs to be assessed further.
  4. The OSLD reader uses software which employs a control dose of 6.4 mrem, which is subtracted from the final semiannual doses. The control dose should only be about 1 or 2 mrem. It is recommended that a control dose of 1.4 mrem be used so that the results reported to ESER will need to be increased by 5 mrem.

Based on these observations, the TLD system will be studied further in 2019 to verify that the negative bias exists and possible sources of this bias. The TLD results will not be reported until this study is completed.

OSLD results from the fourth quarter are reported in Appendix C, Table C-10). OSLDs are presented in dose units of millirem (mrem). Boundary OSLD values ranged from 56.01 mrem at Blue Dome to 68.46 mrem at Mud Lake, with an overall average of 60.99 mrem. Distant results varied from 51.37 mrem at Dubois to 78.25 mrem at Sugar City. The Distant average was 60.81 mrem. The results are about 5 mrem higher than the 2017 results due to the fact the OSLD reader output was adjusted by 5 mrem, to account for a change in the control dose (see bullet #4 above). The second quarter results were also adjusted and the report was revised. 

Radiation in Our World

Radiation has always been a part of the natural environment in the form of cosmic radiation, cosmogenic radionuclides [carbon-14 (14C), Beryllium-7 (7Be), and tritium (3H)], and naturally occurring radionuclides, such as potassium-40 (40K), and the thorium, uranium, and actinium series radionuclides which have very long half lives. Additionally, human-made radionuclides were distributed throughout the world beginning in the early 1940s. Atmospheric testing of nuclear weapons from 1945 through 1980 and nuclear power plant accidents, such as the Chernobyl accident in the former Soviet Union during 1986, have resulted in fallout of detectable radionuclides around the world. This natural and manmade global fallout radioactivity is referred to as background radiation. MORE

Radiation Exposure and Dose

The primary concern regarding radioactivity is the amount of energy deposited by particles or gamma radiation to the surrounding environment. It is possible that the energy from radiation may damage living tissue. When radiation interacts with the atoms of a given substance, it can alter the number of electrons associated with those atoms (usually removing orbital electrons). This is called ionization. MORE