Electrodeposition of Highly Enriched Uranium Thin Films for Advanced Fission Detectors

Abstract Real-time, in-core neutron flux monitoring is essential for characterizing irradiation conditions in research reactors. Micro-Pocket Fission Detectors (MPFDs) operate as an ionization chamber in which a thin fissile coating electrodeposited onto a platinum substrate generates measurable electrical pulses upon neutron-induced fission, enabling continuous, real-time flux monitoring. Optimal sensor performance requires a deposited uranium mass of 0.3 to 1.0 µg, sufficient to produce a measurable fission rate while remaining thin enough to allow fission fragments to escape into the gas cavity. This article describes the electrodeposition of 93% Highly Enriched Uranium (HEU) onto platinum (Pt) substrates to achieve this target mass, along with a standardized protocol for quantifying the deposited mass using alpha-particle spectrometry. The efficiency of thin-film formation by cyclic voltammetry (CV) was compared to bulk electrolysis (BE) to identify the optimal deposition method. ICP-MS independently validated the radiometric mass calculations. Optimizing both the fabrication and quantification techniques facilitates the development of reliable, high-resolution sensors suitable for deployment in diverse research reactor environments.