Vertical soil characterization and migration of radionuclides were investigated at four radioactively contaminated sites on Kirtland Air Force Base (KAFB), New Mexico to determine the vertical downward migration of radionuclides in a semi-arid environment. The surface soils (0–15cm) were intentionally contaminated with Brazilian sludge (containing 232Thorium and other radionuclides) approximately 40 years ago, in order to simulate the conditions resulting from a nuclear weapons accident. Site grading consisted of manually raking or machine disking the sludge. The majority of the radioactivity was found in the top 15cm of soil, with retention ranging from 69 to 88%. Two models, a compartment diffusion model and leach rate model, were evaluated to determine their capabilities and limitations in predicting radionuclide behavior. The migration rates of actinium were calculated with the diffusion compartment and the leach rate models for all sites, and ranged from 0.009 to 0.1cm/yr increasing with depth. The migration rates calculated with the leach rate models were similar to those using the diffusion compartment model and did not increase with depth (0.045–0.076, 0.0cm/yr). The research found that the physical and chemical properties governing transport processes of water and solutes in soil provide a valid radionuclide transport model. The evaluation also showed that the physical model has fewer limitations and may be more applicable to this environment.

The release rates and transformation processes that influence the mobility, biological uptake, and transfer of radionuclides are essential to the assessment of the health effects in the food chain and ecosystem. This study examined concentrations of 222Th in both soil and vegetation at a closed military training site, Kirtland Air Force Base (KAFB), New Mexico. Brazilian sludge was intentionally introduced into the topsoil in the early 1960s to simulate nuclear weapon accidents. Soil (60) and vegetation (120) samples were collected from 1996 to 2000 and analyzed for radionuclides and progeny. High-resolution gamma-ray spectroscopy was used to determine radionuclide activities. The results indicate that the thorium progeny were the predominant contaminant in soil and vegetation. Concentration ratios (CRs) were calculated based on actinium levels.

It has been reported that the mobility of thorium is restricted in plants because of adsorption on cell wall The release rates and transformation processes that influence the material, and that thorium plant concentrations were mobility, biological uptake, and transfer of radionuclides are essential typically several orders of magnitude lower than soil to the assessment of the health effects in the food chain and ecosystem. This study examined concentrations of 232 Th in both soil and vegetation concentrations (CR values in annual grass species range at a closed military training site, Kirtland Air Force Base (KAFB), from 0.001-0.05) (Zararsiz et al., 1997). Risk assessment, New Mexico. Brazilian sludge was intentionally introduced into the remediation, and dose reconstruction models are based topsoil in the early 1960s to simulate nuclear weapon accidents. Soil on concentration ratios that in the case of thorium may (60) and vegetation (120) samples were collected from 1996 to 2000 be significantly underestimated. The objective of this and analyzed for radionuclides and progeny. High-resolution -ray study was to measure thorium progeny in soil and vege- spectroscopy was used to determine radionuclide activities. The results tation and the corresponding CRs derived from these indicate that the thorium progeny were the predominant contaminant measurements. The relative thorium uptake from soil in soil and vegetation. Concentration ratios (CRs) were calculated by plants was calculated as a CR, defined as the ratio based on actinium levels. (unitless) of the plant concentration to the soil concen- tration.