Analytical Sciences

Isotope-selective Microscale Imaging of Radioactive Cs without Isobaric Interferences Using Sputtered Neutral Mass Spectrometry with Two-step Resonant Ionization Employing Newly-developed Ti:Sapphire Lasers

Tetsuo SAKAMOTO,*1 Masato MORITA,*1 Keita KANENARI,*1 Hideki TOMITA,*2 Volker SONNENSCHEIN,*2 Kosuke SAITO,*2 Masaya OHASHI,*2 Kotaro KATO,*2 Tetsuo IGUCHI,*2 Toshihide KAWAI,*3 Takeo OKUMURA,*3 Yukihiko SATOU,*4 and Ikuo WAKAIDA*4

*1 Department of Applied Physics, Kogakuin University, 2665-1 Nakano-machi, Hachioji, Tokyo 192-0015, Japan
*2 Department of Energy Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603, Japan
*3 Japan Neutron Optics Inc., 20-5 Takeshima-cho, Gamagori, Aichi 443-0031, Japan
*4 Collaborative Laboratories for Advanced Decommissioning Sciences, Japan Atomic Energy Agency, 790-1 Otsuka, Motooka, Tomioka, Fukushima 979-1151, Japan

The characterization of radionuclides in Fukushima is important to determine their origins and current state in the environment. Radionuclides exist as fine particles and are mixed with other constituents. A measurement method with both micro-imaging capability and highly selective element detection is necessary to analyze these particles. We developed such an imaging technique using a time-of-flight secondary ion mass spectrometry and wavelength-tunable Ti:Sapphire lasers for the resonance ionization of target elements without mass interference. This is called resonant laser ionization sputtered neutral mass spectrometry. The instrument has a high lateral resolution and a higher ionization selectivity using two-step resonance excitation of Cs with two lasers at different wavelengths. Optimization of the wavelength for resonance ionization using a Cs compound was performed, and a real environmental particle containing radioactive Cs was analyzed. Isotope images of three kinds of Cs were successfully obtained without interfere from Ba isotopes for the first time.

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