| Description |
Neutron activation analysis is a nondestructive method used to determine elemental composition of samples by exposing them to neutron radiation, which leads to the activation of stable nuclei into radioactive nuclei. During deactivation of irradiated samples, element-signature gamma rays are emitted that are detected using gamma spectroscopy. The main goal of this dissertation is to develop detailed modeling of neutron activation analysis in predicting gamma spectra of various samples using MCNP6 and GEANT4 (version 4.9.6) codes. High precision physics models for neutron transport and ENDF/B-VII evaluated cross-sectional data library are used in both MCNP6 and GEANT4 simulations. These newly developed models are validated based on the experimental data of a National Institute of Standard and Technology (NIST) certified flyash sample and six samples with varying compositional matrices. These models predict the gamma spectra of activated samples with good agreement to measured gamma spectra. Thus, both codes, MCNP6 and GEANT4, can be used to predict neutron induced gamma emissions in samples of various compositions prior to neutron activation analysis taking place in the laboratory settings. The relative computational error is within 5 - 8%, which falls within the Monte Carlo accepted computational limit of 10%. Another goal of this dissertation is to develop an explorative study of a large sample analysis based on neutron activation and to assess the feasibility of such experiments in research reactors, specifically the TRIGA Mark I type research reactors. The Utah Nuclear Engineering Program houses a 100 kW TRIGA Mark I research reactor with irradiation channels that were not studied for large sample neutron activation analysis. The newly developed MCNP6/GEANT4 models provide 3D point-wise spatial neutron flux distributions within irradiation channels. These models are adequate in simulating experiments prior to taking place in the laboratory. The neutron flux intensities are adequate for large sample analysis in one of the reactor irradiation channels. |
