Isotope ratio analysis of micron sized uranium particle by Large Geometry Secondary Ion Mass Spectrometry instrument

Tomita, Ryohei ; Esaka, Fumitaka  ; Yasuda, Kenichiro   ; Suzuki, Daisuke   ; Miyamoto, Yutaka   

The research group for safeguards analytical chemistry which belong to Japan Atomic Energy Agency (JAEA) introduced new Large Geometry Secondary Ion Mass Spectrometry (LG-SIMS) instrument (1300-HR, CAMECA) to update our capability. LG-SIMS instrument has higher mass resolving power (MRP) than small geometry SIMS (SG-SIMS) instrument we had used. We hope molecular interferences (e.g. Pb, Al, Fe) are removed by LG-SIMS instrument when we analyze uranium bearing particles in environmental sample. In order to obtain the bes LG-SIMS condition for uranium particle analysis, we investigated a relationship between MRP, secondary ion's intensity and peak shape of uranium. One of the most famous molecular interferences of uranium SIMS analysis is PbAl (mass number: 234, 235). If we attempt to remove molecular interferences of the PbAl from uranium mass regions, MRP value of 2741 is required. The MRP of LG-SIMS instrument is defined by entrance and exit slit. We need to keep balance between MRP, secondary ion's intensity and flat-top peak rate. We compared some combination of entrance and exit slit to get better balance. We found the best combination of entrance and exit slit is sized 200 m and 500 m, respectively. LG-SIMS can almost remove PbAl from uranium secondary ions in this condition. This research is part of investigation into safeguards analysis techniques commissioned by nuclear regulatory agency.