Creating and Validating Models for the Detectors Housed in the Radiometric Assay and Detection Lab (RADLab)

Fusion energy will be transformative to the energy landscape. To reach a stage where a commercial fusion power plant is viable, materials research is key to establishing how different materials can survive in harsh fusion environments (high temperatures, intense magnetic fields, and high neutron fluences) and the implications for fusion waste. Gamma spectroscopy is a primary diagnostic technique that will provide critical insight into the effects of exposing materials to high neutron fluences. This is an industry standard non-destructive technique employed to measure gamma radiation from neutron-activated materials and can be used to infer neutron flux and material performance in a fusion environment. The Radiometric Assay and Detection Lab (RADLab) at UK Atomic Energy Authority (UKAEA) houses state-of-the-art HighPurity Germanium (HPGe) gamma spectrometers for both lab-based and in-situ measurements. Gamma spectroscopy relies on accurate modelling of detectors and the measurement geometry to apply an efficiency correction to measurements. This work focused on modelling RADLab HPGe detectors in MCNP (Monte Carlo N particle) with results validated against other techniques such as OpenMC, Ortec's ISOTOPIC and Mirion's In-Situ Object Counting System (ISOCS) software. The ability to model using codes like MCNP and OpenMC with confidence would allow detailed modelling of complex geometry and materials and integration with existing complex models that are not currently possible with proprietary software. A comparison between the modelling approaches will be presented, using mixed nuclide sources containing fusion-relevant radionuclides.