Validation of LG-SIMS analysis of plutonium-bearing particles using Pu-impregnated silica particles and its application to the Daigo Fukuryu-Maru sample

Tomita, Ryohei ; Tomita, Jumpei  ; Yomogida, Takumi   ; Suzuki, Daisuke   ; Takamiya, Koichi*; Igarashi, Yasuhito*; Yamasaki, Shinya*; Sakaguchi, Aya*; Yasuda, Kenichiro   

Plutonium (Pu) isotopic ratio analysis of individual particles is essential for nuclear safeguards and environmental investigations. A large geometry secondary ion mass spectrometry (LG-SIMS) methodology was developed and validated using Pu-impregnated porous silica particles as surrogate reference materials. The validated method was applied to an iron rust sample collected from the Daigo Fukuryu-Maru (Lucky Dragon No. 5), contaminated by Castle Bravo fallout in 1954. Although SEM-EDX failed to identify U- or Pu-bearing particles, LG-SIMS screening detected six Pu-bearing particles for isotopic characterization. Five particles exhibited Pu/Pu ratios of 0.2810.0050.3100.002, whereas one showed a lower ratio of 0.1980.005. The results demonstrate the applicability of LG-SIMS to ultra-trace environmental Pu particles and reveal previously unresolved isotopic heterogeneity associated with Marshall Islands fallout.