Portland State University. Department of Geology.
Scott F. Burns
Term of Graduation
Date of Publication
Master of Science (M.S.) in Geology
Radioactive substances in soils, Radon -- Environmental aspects, Soils -- Oregon
1 online resource (x, 220 pages)
Radon, a naturally occurring radioactive gas produced as one of the decay products of soil/rock uranium and thorium, is considered to be a leading cause of pulmonary disease. Gamma spectrometry of 146 samples of soil were used to quantify radon source potential relative to lithology by measuring Bi214 activity of the U238 decay series. Additional soil radio nuclide data (Th232, Ac228, K40 and C137 ) were used to help identify regional source provenance geochemistry and soil development. Ac228, Bi214 and Th232 activities in northwest Oregon soils range from five to 55 Bq/kg, while K40 activities range from 53 to 750 Bq/kg.
In northwest Oregon, three radon potential zones are defined by soil Bi214 activity: 62% falls within Low 1 zones (less than 25 Bq/kg), 35% falls within Low 2 zones (25 to 45 Bq/kg) and 3% falls within Moderate zones (greater than 45 Bq/kg). Low 1 zones are significantly influenced by proximal volcanic source provenances, while Low 2 zones and Moderate zones are considered to reflect distal plutonic and/or metamorphic source provenances.
Soil radionuclide activity has been shown to vary with soil development. Th232 :K40 soil activity ratios and Bi214 soil activity are found to increase with soil development. Th232 :K40 soil activity ratios of soils developed on, or from previously unweathered rock and sediment range between 0.03 and 0.08. Th232 :K40 activity ratios of soils developed on, or from previously weathered rock and sediment are often greater than 0.12. Soil radionuclide activity data of this study do not identify areas with known elevated indoor radon. Soil permeability data provided by the Soil Conservation Service (SCS) do identify the Alameda Ridge area of north and northeast Portland, an area with known elevated indoor radon. In Salem, Soil Conservation Service soil permeability data do not identify areas with elevated indoor radon. However, some areas of Salem with elevated indoor radon have landslides capable of affecting subsurface permeabilities. There is a possibility that subsurface soil permeabilities, favorable for convective soil gas transport and elevated indoor radon, exist at depths greater than those measured by the Soil Conservation Service.
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Ashbaugh, Stuart Graham, "The Distribution of Naturally Occurring Soil Radionuclides and Radon Potential of Northwest Oregon" (1995). Dissertations and Theses. Paper 5015.
Plate 1. Radon Potential Zones of Northwest Oregon
Ashbaugh_Plate2.pdf (11070 kB)
Plate 2. Site Locations of Samples
Ashbaugh_Plate3.pdf (18454 kB)
Plate 3. Radon Potential Zones of Portland, Oregon
Ashbaugh_Plate4.pdf (15815 kB)
Plate 4. Radon Potential Zones of Salem, Oregon