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Report No.
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The Method to reduce particle mixing under automated particle measurement (APM) condition of LG-SIMS

Tomita, Ryohei ; Esaka, Fumitaka ; Yomogida, Takumi  ; Miyamoto, Yutaka  

Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS) is one of the strongest tools for analyzing isotope ratios of micron sized uranium particle. LG-SIMS has high spatial resolution of less than 1 $$mu$$m with microprobe mode. However, this capability is bit less under automated particle measurement (APM) condition. If two or more particles are located in a quite narrow area, APM may detect the cluster as one particle. This particle mixing effect shows analytical results including false isotope ratios. In order to investigate how often particle mixing happens and how to solve this problem, we implemented APM to mixed uranium particle standard (U010, U100, U350 and U850) and try to apply particle manipulation with APM. In our experiment, each area (350$$times$$350 $$mu$$m$$^{2}$$) was scanned with an O$$^{2+}$$ primary beam with a current of 1.5 nA for 9 sec. Then, secondary ion images were recorded for circular area with a radius of 8500 $$mu$$m on the center of a sample planchet. The APM detected 5976 particles, and 1943 particles (32%) in them showed false isotope ratios. In addition to particle mixing, U850 cluster was shifted down to around 75% enrichment. The sample showed too high hydride rate, so that $$^{235}$$UH interfered $$^{236}$$U. This interference caused false $$^{236}$$U abundance and lead to false $$^{235}$$U abundance. To solve these problems, 50$$sim$$80 particles were manipulated randomly from another mixed standards planchet and analyzed them by APM.

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