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 (Bq/m2)※1	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.

Related articles

• Where were radioactive materials deposited and in what quantities?
• What kinds of radioactive materials were released into the atmosphere and the sea and how much?
• How has the distribution of radioactive material been investigated?
• How is the concentration of radioactive Cs measured?
• In what ways does exposure to radiation occur the environment? What kinds of radiation exposures are important in Fukushima?

Reference

1. 文部科学省　原子力災害対策支援本部、農林水産省　農林水産技術会議事務局「『東京電力株式会社福島第一原子力発電所の事故に伴い放出された放射性物質の分布状況等に関する調査研究結果』の簡略版について」,2012年3月13日