Total evaporation for uranium particles generating much uranium hydride formation and isotopic ratio change

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

Secondary ion mass spectrometry (SIMS) analysis of uranium particles for safeguards purpose consists of Automated Particle Measurement (APM) and Microprobe analysis. APM for safeguards sample includes 2400 measurements, each field is analyzed for short time. So, if a sample have particles which generate too much uranium hydride formation on their surface, the APM result, especially U abundance, is affected by uranium hydride formation. It causes inaccurate APM result. To investigate what percentage of the entire particle the particle surface causing ratio change account for, total evaporation measurement was implemented for standard uranium particle generating much uranium hydride formation on their surface and uranium isotopic ratio change during the total evaporation measurement was observed. Total evaporation experiment indicated that the number of secondary ions originated from particle surface accounted for 3.1% of all of number of ions sputtered from the entire particle. Based on the total evaporation result, APM conditions, primary beam intensity, measurement time and raster size, combined with the method manipulating particles under scanning electron microscope were optimized to reduce the hydride effect for APM result.