To date, guidance for environmental assessment using experimental radiation detection techniques – specifically relating photon detector responses to dose or cancer risk-based radionuclides concentrations in environmental media – exist under the Environmental Protection Agency (EPA) Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). To address this technical challenge, a modeling research effort was undertaken to estimate thousands of sodium iodide thallium-doped (NaI(Tl)) detector total efficiency responses in the development of a detector response function (DRF) methodology to calculate detector responses from simulated contamination in various geometries in environmental media. Ultimately, currently expensive and time-consuming sample collection and laboratory analyses efforts required for demonstrating regulatory compliance in future radiological site remediation applications may be reduced when referencing the data calculated in this study in the field.
This work results from a comprehensive study that consists of multiple auxiliary efforts following the development of the DRF methodology, which we refer to as “Shift with CADIS.” A study was conducted to analyze the effectiveness of Shift with CADIS compared to various radiation transport variance reduction (VR) methods for improved modeling in future wide-area contamination assay applications. Additionally, a method was developed for estimating the total detector efficiency response contribution from secondary photons arising from electron source emissions (called bremsstrahlung) in soil with Monte Carlo (MC) simulation, which employed the electron transport condensed history method in a computationally feasible manner. Lastly, investigatory measurements were performed with laboratory-scale setups of low-level activity environmental soil contamination with field surrogate photon source terms to validate simulated detector efficiency responses.