Studies on treatment methods of the safeguards swipe samples for uranium isotope ratio measurement

Takahashi, Masato; Magara, Masaaki  ; Sakurai, Satoshi ; Kurosawa, Setsumi; Sakakibara, Takaaki; Hanzawa, Yukiko  ; Esaka, Fumitaka  ; Watanabe, Kazuo; Usuda, Shigekazu; Adachi, Takeo

In the environmental sampling and analyses for safeguards, precise isotope ratio determination of uranium at trace levels is required for detection of undeclared nuclear activities. Currently, swipe samples are being taken by IAEA from the nuclear facilities. The amount of uranium collected on the cotton swipe is expected to be in the wide range including the order of nano-gram or less. In order to measure the isotope ratios by ICP-MS, we have studied sample preparation procedures. Four pretreatments of swipe samples were examined: 1) nitric acid leaching, 2) dry ashing, 3) low-temperature plasma ashing, and 4) acid digestion. Preliminary results showed that the combination of 3) and 4) was favorable from the points of uranium blank, cross-contamination, chemical yield and manipulation conditions in a clean laboratory. It was found that the cotton swipe contained nano-gram levels of uranium as impurity. Since this value may seriously interfere with the isotopic analysis of uranium, selective recovery of the deposited uranium by means of mechanical method is also studied.