Analytical Sciences

Assessing the Effect of Laboratory Environment on Sample Contamination for I-129 Accelerator Mass Spectrometry

Masumi MATSUMURA,* Kimikazu SASA,* Tetsuya MATSUNAKA,** Keisuke SUEKI,* Tsutomu TAKAHASHI,* and Hiroyuki MATSUZAKI***

*Tandem Accelerator Complex, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
**Institute of Nature and Environmental Technology, Kanazawa University, 24 O, Wake, Nomi, Ishikawa 923-1224, Japan
***The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo, Tokyo 113-0032, Japan

Environmental contaminations of ¹²⁹I were continuously monitored in various sample preparation rooms for accelerator mass spectrometry at the University of Tsukuba. Monitoring of ¹²⁹I was performed in the rooms used for the treatment of samples in the past, in order to compare with the results obtained in the sample preparation rooms. Ambient levels of atmospheric ¹²⁹I in each room were estimated from the measured concentrations in the alkali trap solutions. This article reports the results of one year of monitoring the temporal changes of stable iodine (¹²⁷I) and ¹²⁹I contamination rates in the alkali trap solutions. It was found that ¹²⁹I contamination rates were lower than approximately 10⁴ atoms cm⁻² day⁻¹ in the rooms where ether no samples or only samples with environmental background levels of ¹²⁹I were handled. Values from 10⁴ to 10⁵ atoms cm⁻² day⁻¹ were recorded in another room where environmental samples, such as the samples derived from nuclear power plant accidents, were treated. Higher levels of ¹²⁹I, ranging from 10⁶ to 10⁷ atoms cm⁻² day⁻¹, were recorded in rooms used for treating neutron-activated iodine. The experimental results show that the ¹²⁹I level depended on the ¹²⁹I sample-preparation histories for the respective rooms. It is possible to estimate the ¹²⁹I contamination risk from the atmosphere to the samples by knowing the ¹²⁹I level in the preparation room.

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