Unlocking actinide pre-concentration potential and unique α-scintillation properties of an inorganic nanotube–polyethersulfone membrane composite: a viable sensing platform for environmental nuclear forensics

Abstract

Radiometric assay of environmental samples has become an indispensable tool for nuclear safeguard and security. In spite of the availability of different radiometric techniques, the current limiting factor is the lack of efficient separation materials to prepare samples for radiometric analysis directly from environmental samples. Herein, we demonstrated the potential of methyl-functionalized aluminosilicate nanotubes (commonly known as methyl imogolite or Imo-CH₃) for sequestering uranium and plutonium ions by arresting them from dilute aqueous solutions in the form of insoluble hydroxides under alkaline conditions, which subsequently formed an optically transparent thin film on a microporous PES membrane upon syringe filtration. Contrary to their individual counterparts, the PES-Imo-CH₃ composite was found to show a unique α-scintillation property in the presence of the arrested actinides, which was used for gross α-radioactivity estimation at sub-Becquerel levels with a limit of detection of 2.5 mBq mL⁻¹. The interaction and energy loss characteristics of α-particles in the PES-Imo-CH₃ composite were simulated using the Monte Carlo method, which suggested that the observed scintillation is a result of indirect excitation of the Imo-CH₃ nanotubes via a non-radiative energy transfer pathway. The PES-Imo-CH₃ composite, used for gross scintillation counting, was also demonstrated as a potential α-spectrometry platform, thus reducing the sample preparation steps and minimizing the nuclear forensic analysis timeline. The actinide sequestration efficiency of the nanotubes was found to be 97.2 ± 1.2% for U and 99.5 ± 8.2% for Pu within the studied range of radioactivity concentrations with negligible selectivity between actinide elements, making it particularly unique for nuclear forensic applications, where preserving the isotopic and elemental ratios are key requirements.