Minute quantities of radio isotopes are ceaselessly formed on the surface of our earth by the effect of cosmic rays, circulate within the environment and disappear according to their decay time. Therefore, it is possible to use radio isotopes as a clock to reveal the time scale of the circulation of the elements and substances in the environment and to determine the age of sediments. Also from the radioactive carbon density within the toxic chemicals, it is possible to clarify whether they originate from fossil fuels (containing no 14C) or not.
However, the natural abundance of radio isotopes produced by cosmic rays within our environment is extremely low, thus it is a difficult task to measure cosmic ray-produced radio isotopes by conventional radioactivity measurements. For example, there are over one-billion 14C atoms within one gram of a plant leaf, but the number of beta rays which are emitted from them are only two or three per minute. Thus to accurately obtain the quantity of 14C from beta ray measurements requires a large sample and a long period of time. On the other hand, if there were a means to count the number of atoms directly, the measurements would be much more efficient. A method developed for this task is accelerator mass spectrometry (AMS).
The tandem accelerator analysis facility at NIES (National Institute for Environmental Studies) is a facility that enables AMS analysis for environmental research. Taking the abbreviation for Tandem accelerator for Environmental Research and Radiocarbon Analysis, it is called NIES-TERRA. TERRA means "earth" in Latin. Aiming for the promotion of environmental research, thus literally making it a research base for "understanding the earth" and environment.
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