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Why Radioactive Cesium?

Why Radioactive Cesium?

By Fukushima-Daiichi Nuclear Power Plant Accident, radionuclides generated in the reactor were released into wide environment around Fukushima prefecture, and large amount of radionuclides are still remained.

To understand the relative importance of each radionuclide on exposure, exposure dose were estimated under the extreme condition that people stands 50 years on maximum deposition point, which method is suggested by International Atomic Energy Agency, IAEA.

As a result, 137Cs and 134Cs in several isotopes of cesium were estimated to contribute exposure dose more than other radionuclides, because they have relatively long half-life and high concentration.

And also it was suggested that targeting these radionuclides are suitable for assessment of exposure dose and countermeasures of decontamination.

Under these circumstances, the environmental dynamics research by JAEA targets 137Cs and 134Cs.

Radionuclides Half-life Maximum Concentration
Estimated cumulative effective dose in 50 years(mSv)
134Cs 2.065 y 1.4×107 710
137Cs 30.167 y 1.5×107 2,000
131I 8.02 d 5.5×104 0.015
89Sr 50.53 d 2.2×104 0.00061
90Sr 28.79 y 5.7×103 0.12
238Pu 87.7 y 4.0 0.027
239Pu + 240Pu 2.411×104 y 15.0 0.12
110mAg 249.95 d 8.3×104 3.2
129mTe 33.6 d 2.7×106 0.6

※1:Radioactivity is corrected for their decay as of June 14, 2011.

Some elements has several mass number because of the number of neutron. They are called "isotope" and distinguished by the appended number which shows their mass number, i.e., 137Cs and 134Cs.