Predictive Radiological Background Distributions from Geochemical Data
Abstract
Gamma ray surveys are an important tool for both national security interests as well as industry in determininglocations of both anthropogenic radiological sources and natural occurrences of radiologic material. The purpose ofthis project is to predict the radiologic exposure rate of geologic materials by creating a model using publishedgeochemical data, geologic data, GIS software, and freely available remote sensing data sets. If K, U, and Thabundance values are known for a given geologic unit, the expected radiation exposure rate can be calculated. Oneof the primary challenges surrounding this project is that alluvial units are classified by age rather than rock type. Itis therefore important to determine sediment sources and estimate their relative contribution to alluvial units.ASTER data from the Terra satellite can differentiate between surface mineralogies and can aid us in calculating therelative percentage of sediment from each source and by extension the geochemical concentrations of challengingsurfaces such as alluvium. An additional problem is that U and Th do not directly contribute to the measuredradiation exposure rate. Instead, daughter isotopes of these radioelements emit detectable gamma rays and may nothave reached equilibrium in younger surfaces. U can take up to 1.5 Ma to come to equilibrium with its daughterisotopes while Th takes only about 40 years. Further modeling with software such as Monte Carlo N-ParticleTransport from Los Alamos National Laboratory, will help us correct for this disequilibrium in our models. Once the predicted exposure rate is calculated for a geologic unit, it can then be assigned to a geographic area basedon geologic and geomorphic trends. This prediction will be subtracted from data collected through aerial surveys,effectively ignoring geology, and allowing areas of interest to be narrowed down considerably. The study areasinclude the alluvium on the west shore of Lake Mohave and Government Wash north of Lake Mead. In both of theseareas, strategically located soil and rock samples have been collected and are awaiting geochemical analysis. This work was done by National Security Technologies, LLC, under Contract No. DE-AC52-06NA25946 with theU.S. Department of Energy. DOE/NV/25946--2117
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2014
- Bibcode:
- 2014AGUFMNH11B3711H
- Keywords:
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- 4331 Disaster relief;
- 4335 Disaster management;
- 4337 Remote sensing and disasters;
- 4339 Disaster mitigation