Uranium Particle Identification with SEM-EDX for Isotopic Analysis by Secondary Ion Mass Spectrometry

Abstract

: Secondary ion mass spectrometry (SIMS) is a promising tool to measure isotope ratios of individual uranium particles in environmental samples for nuclear safeguards. However, the analysis requires prior identification of a small number of uranium particles that coexist with a large number of other particles without uranium. In the present study, this identification was performed by scanning electron microscopy -energy dispersive X-ray analysis with automated particle search mode. The analytical results for an environmental sample taken at a nuclear facility indicated that the observation of backscattered electron images with × 1000 magnification was appropriate to efficiently identify uranium particles. Lower magnification (less than × 500) made it difficult to detect smaller particles of approximately 1 µm diameter. After identification, each particle was manipulated and transferred for subsequent isotope ratio analysis by SIMS. Consequently, the isotope ratios of individual uranium particles were successfully determined without any molecular ion interference. It was demonstrated that the proposed technique provides a powerful tool to measure individual particles not only for nuclear safeguards but also for environmental sciences.

Analysis of particles containing alpha emitters in stagnant water in Fukushima Daiichi Nuclear Power Station’s Unit 3 reactor building

“…Detection and analysis of U-containing particles by SEM–EDX was performed, as described in our previous study 19 . The automatic particle finder 42 used in SEM–EDX identified U-containing particles larger than 1.0 µm in diameter from the same sample used for the alpha track analysis. The field of view was fixed by observing the BSE image of a part of the sample at a magnification of 1500×.…”

Analysis of particles containing alpha-emitters in stagnant water at torus room of Fukushima Dai-ichi Nuclear Power Station’s Unit 2 reactor

“…The same sample that had been used to complete alpha track analysis was used for U-containing particles larger than 0.5 µm in diameter using the automatic particle finder 17 of the SEM-EDX. First, the field of view was fixed by observing the back-scattered electron image of part of the sample for observation at a magnification of ×1500.…”

“…However, while these methods are effective for CsMPs with high radioactivity, it is difficult to selectively detect α-emitters that are present in small amounts and with low specific radioactivity. Therefore, we decided to use a combination of an automated particle measurement method using SEM-EDX 17 and a method for detecting particles containing α-emitters using solid-state track detectors 18 – 24 .…”

Identification of microscopic uranium particles using fission tracks in nuclear solid-state detectors

“…An important preliminary step before conducting isotopic analysis of individual particles is to determine their location and identification in a sample covered with a large quantity of nonspecific environmental dust. While particle screening can be performed using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDX), 6 SIMS is the only method that both localizes the particles and provides their isotopic composition. 7 There are several factors limiting the performance of those two particle-screening methods.…”