Development of a micro separation and analysis system for uranyl ions composed of microplug extraction and liquid scintillation detection

Abstract

The efficient separation and analysis of alpha-emitting radionuclides, which will reduce environmental and radiation workers’ workloads, is of growing importance in the conducting of safe and long-term nuclear decommissioning and environmental assessments. This study developed a novel analytical system comprising micro-extraction and liquid scintillation counting (LSC), capable of rapidly and simply analyzing alpha nuclides in small amounts of samples. Bulk extractions and micro-extractions of UO₂²⁺ were performed using two types of extractive liquid scintillators containing bis(2-ethylhexyl) phosphate (HDEHP) and N,N,N′,N′-tetra-octyldiglycolamide (TODGA) ligands. The UO₂²⁺ extraction rates were evaluated through inductively coupled plasma-optical emission spectrometry (ICP-OES) and LSC measurements. When measuring LSC spectra of the bulk-extracted organic scintillator phases, peaks assigned those of ²³⁸U and ²³⁴U isotopes were clearly observed. The peak intensities and counting rates increased linearly with increasing UO₂²⁺ concentrations, confirming that the UO₂²⁺ extraction rates determined from LSC measurements agreed well with those from ICP-OES. From the LSC spectra and counting rates of micro-extracted samples, it was confirmed that the HDEHP-type extractive scintillator achieved 100% extraction of UO₂²⁺ within 20 s in the lower HNO₃ concentration ranges, which was more than 90 times faster than bulk extraction (30 min), and that quantitative analysis of uranium using LSC was feasible up to 3 M HNO₃. The results demonstrate that the microfluidic-LSC approach has significant potential as an advanced separation−analysis method. It enables direct measurements of alpha-emitting radionuclides in organic phases without additional operations such as pretreatment and back-extraction.

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