Development of analytical methods for trace radionuclides in environment
Interviewee
Makoto Matsueda
Research purpose and contents
Our group has researched the environmental dynamics of radionuclides that were released from the Fukushima Daiichi Nuclear Power Station (FDNPS). We used to develop analytical methods and research the behaviors for cesium-137 and strontium-90 with a half-life of about 30 years. We also focused on technetium-99 (99Tc) that exists for a long period in case of release to the environment, because of the long half-life of 210,000 years. In addition, while 99Tc has high mobility and distributed widely in the environment, accumulates to fishery products such as seaweed. Thus, it is required that the monitoring of 99Tc in wide areas surrounding the FDNPS. However, the development of an original technique is necessary for monitoring since there is no official method for 99Tc in Japan. Furthermore, 99Tc is an artificial radionuclide that had not existed in nature, and the background level is extremely low. Therefore, we are developing a sensitive and simple analytical method for 99Tc applied for long-term monitoring. Finally, we aim to build a modeling system based on the analytical results of environmental samples using the developed method.
Analytical Methods for radionuclides
Radionuclides are mainly determined by radioactivity analysis or mass spectrometry. In the case of 99Tc, radioactivity analysis measures the beta-ray emitted from 99Tc. However, it is required a large sample volume for measuring the practical level of 99Tc in the environment. Moreover, other beta-ray nuclides except for 99Tc prevent quantification by signal overlap, and the separating of interferences is required with a complex operation. On the other hand, mass spectrometry such as inductively coupled plasma mass spectrometry (ICP-MS) has the advantage of high sensitivity with a small volume. However, the isobaric interferences detecting as mass 99 (99Ru and 98Mo1H) must be separated.
inductively coupled plasma mass spectrometry (ICP-MS)
online solid-phase extraction ICP-MS system
Online solid-phase extraction ICP-MS system
We developed a fully-automated analytical system: the "online solid-phase extraction ICP-MS system." In this system, a specific resin with selectivity for 99Tc removes interfering nuclides such as 99Ru. Subsequently, 99Tc is eluted from the resin and introduced into ICP-MS. In addition, we developed a technique of a dynamic reaction cell (DRC) with oxygen gas to remove 98Mo1H formed in the ICP-MS. The technique enables the accurate detection of 99Tc. The analysis time was reduced to less than 15 minutes. The actual environmental samples such as river water and seawater spiked with 99Tc were measured using the system and the results are agreed with expectations.
online solid phase extraction ICP-MS system Flow chart
The "online solid-phase extraction ICP-MS system" is fast and fully automated, but its sensitivity is inadequate to measure background levels in the environment. Previously reported methods required a 200 L per seawater sample to analyze 99Tc in the environment. We will create a sensitive method to measure with only several liters and utilize it to study the environmental dynamics of 99Tc after the FDNPS accident. Moreover, we aim to develop a method to be employed as the official method for 99Tc in Japan.