Measurement Results of Ambient Radiation Levels in the City

Regarding the Change in the Frequency of Measuring Ambient Radiation Levels in the City

Since the occurrence of the Great East Japan Earthquake, the city has been continuously conducting fixed-point measurements of ambient radiation levels at 5 cm and 100 cm above ground in the city's Elementary and Junior High Schools, Nursery Schools, and Kindergartens since June 2011. However, due to the current measurement values being below the standard value indicated by the Ministry of the Environment (0.23 microsieverts per hour), and the fact that the values from the radiation monitoring posts in Shinjuku, which were established before the Great East Japan Earthquake, have decreased to pre-earthquake levels, we will suspend the measurements of ambient radiation levels in the city from the fiscal year 2021 onwards. However, if any concerns arise, we will immediately resume measurements.

For more details, please see the link below.

• Regarding the change in the measurement frequency of indoor radiation levels(external link)

For the results of the monitoring posts in Shinjuku Ward, please check the link below.

• About the Shinjuku Ward Radiation Monitoring Post(External Link)

Measurement Results of Ambient Radiation Levels

After changing the measurement frequency, we conducted measurements of the ambient radiation levels in the city, and we will publish the results.

The measurement results were below the reference values recommended by the International Commission on Radiological Protection.

Measurement Location	Measurement Date	Weather	Measurement (Unit: μSv/h) Playground or Garden (Height above ground) 100cm	Measurement (Unit: μSv/h) Playground or Garden (Above Ground Level) 5cm
Daiichi Elementary School	January 6, 2021	Clear	0.053	0.045
Daini Elementary School	January 5, 2021	Cloudy	0.041	0.043
Third Elementary School	January 13, 2021	Clear	0.048	0.050
Daiyon Elementary School	January 18, 2021	Cloudy	0.050	0.048
Dairokusho Elementary School	January 4, 2021	Clear	0.056	0.054
Seventh Elementary School	January 5, 2021	Cloudy	0.038	0.040
Koyodai Elementary School	January 4, 2021	Clear	0.031	0.033
Shiroyama Elementary School	January 14, 2021	Clear	0.031	0.032
Nagamine Elementary School	January 7, 2021	Clear	0.032	0.035
Wakabadai Elementary School	January 6, 2021	Cloudy	0.037	0.037
Hirao Elementary School	January 7, 2021	Clear	0.043	0.039
Minamiyama Elementary School	January 18, 2021	Cloudy	0.056	0.060
Daiichi Junior High School	January 4, 2021	Clear	0.059	0.063
Daini Junior High School	January 6, 2021	Cloudy	0.043	0.047
Third Junior High School	January 7, 2021	Clear	0.053	0.056
Daiyon Junior High School	January 14, 2021	Clear	0.045	0.045
Fifth Junior High School	January 5, 2021	Cloudy	0.040	0.032
Dairokuchu School	January 6, 2021	Cloudy	0.055	0.056
Third Nursery School	January 8, 2021	Clear	0.033	0.035
Fifth Nursery School	January 6, 2021	Cloudy	0.039	0.035
Sixth Nursery School	January 13, 2021	Clear	0.06	0.07
Hirao Nursery School	January 13, 2021	Clear	0.04	0.04
Matsuba Nursery School	January 13, 2021	Clear	0.05	0.05
Koyodai Nursery School	January 14, 2021	Clear	0.05	0.05
Shiroyama Nursery School	January 13, 2021	Clear	0.05	0.05
Nagamine Nursery School	January 13, 2021	Clear	0.07	0.06
Wakabadai Baobab Nursery School	January 13, 2021	Clear	0.06	0.06
Mominoki Nursery School Wakabadai	January 13, 2021	Clear	0.05	0.06
Nakajima Yushi Nursery School	January 13, 2021	Clear	0.05	0.04
Nanyama Nursery School	January 14, 2021	Clear	0.05	0.04
Hongo Yushi Nursery School	January 13, 2021	Clear	0.08	0.1
Felice Inagi Nagunuma Garden	January 14, 2021	Clear	0.07	0.07
Aoba Kindergarten	January 14, 2021	Clear	0.07	0.07
Komakusa Kindergarten	January 14, 2021	Clear	0.06	0.06
Komazawa Women's Junior College Attached Komazawa Kindergarten	January 14, 2021	Clear	0.06	0.06
Hanabusa Kindergarten	January 14, 2021	Clear	0.05	0.05
Hirao Wakaba Kindergarten	January 14, 2021	Clear	0.05	0.05
Yano Kuchi Kindergarten	January 13, 2021	Clear	0.05	0.06
Rika Kindergarten	January 14, 2021	Clear	0.06	0.05

Note: When converting 0.23 microsieverts per hour to an annual equivalent, it amounts to 0.99864 millisieverts. According to the recommendations of the International Commission on Radiological Protection (ICRP), this value is below the indicator for the radiation dose that the general public is exposed to during normal times (less than 1 millisievert per year, excluding natural background radiation). Therefore, this value is used as the city's judgment criterion. However, based on the measured values, the annual equivalent was calculated to be less than 0.526 millisieverts (including natural background radiation, etc.), resulting in a value of less than 1 millisievert per year (excluding natural background radiation, etc.).

Measurement Overview

Measurement Location

Municipal Elementary and Junior High Schools, Municipal and Private Nursery Schools, Private Kindergartens

Measurement Location

Schoolyard or Garden

Measurement Height, etc.

Height of 5 centimeters and 100 centimeters from the ground surface

Measurer

City Employee

Measuring Equipment

• PA-1000 (Elementary and Junior High Schools)
• TCS-172B (Nursery School - Kindergarten)

Note: The number of digits in the measurement values varies depending on the measuring instrument used. (PA-1000 displays three decimal places, TCS-172B displays two decimal places.)
For your reference: Comparisons of measurement values using multiple measuring instruments are being conducted at the Tokyo Metropolitan Health Safety Health Center.
For more details, please see "We measured the grounds of the Health Safety Research Center with various types of radiation measuring instruments."

• We measured the grounds of the Health and Safety Research Center using various types of radiation measuring devices.(External link)

Measurement Method

• Average of 5 repeated measurements every 60 seconds (PA-1000)
• Average of 5 repeated measurements every 30 seconds (TCS-172B)

Measurement Values

Unit: MicroSieverts per hour

Future Measurements

Since there was no significant change in the values based on height from the first measurement conducted on June 28, 2011, subsequent measurements have been carried out at 5 centimeters and 100 centimeters above the ground surface.

Estimation of Annual Equivalent Dose of Ambient Radiation

Regarding the annual estimated value of ambient radiation levels in the city, we have calculated it based on the condition that the "ambient radiation measurement results in the city" continued for one year.

Annual Conversion Value Estimation Method

Annual conversion value (millisieverts per year) = (measured value - natural radiation level) × (8/24 [time spent outdoors] + 16/24 [time spent indoors] × 0.4 [indoor radiation reduction rate]) × 24 hours × 365 days ÷ 1000 [milligram conversion]

《In the case of 0.090 microsieverts per hour》
⇒0.090×(8/24【Time spent outdoors】+16/24【Time spent indoors】×0.4【Reduction rate of radiation indoors】)×24 hours×365 days÷1000≒0.473 millisieverts per year
Note: This conversion value does not account for natural radiation levels.
［Reference］The average natural radiation level in the country is said to be around 0.04 microsieverts per hour.

Conditions

• Assuming 8 hours outdoors and 16 hours indoors in a wooden house
• Reduction effect (coefficient 0.4) during stay in wooden house (16 hours)

Note: The estimates are based on the measured values from the locations where measurements were conducted this time, assuming they continue for one year.

Glossary

• Sievert (Sv) - A unit that represents the biological effects of radiation
• Millisievert (mSv) - a unit that is one-thousandth of a sievert
• Micro sievert (μSv) - a unit that is one millionth of a sievert (one thousandth of a milli sievert)

ICRP (International Commission on Radiological Protection) Standards

• Emergency: 20 millisieverts to 100 millisieverts per year
• Post-emergency recovery: 1 millisievert to 20 millisieverts per year
• Normal times: less than 1 millisievert per year

Note: The above ICRP standards do not include radiation doses from natural radiation or medical procedures.

Past Measurement Results

• Measurement Results [Fiscal Year 2 Implementation] (PDF 135.3KB)
• Measurement Results [Conducted in October of the 2nd Year of Reiwa] (Excel 13.7KB)
• Measurement Results [Conducted in July of the 2nd Year of Reiwa] (PDF 113.3KB)
• Measurement Results [Conducted in April of the 2nd Year of Reiwa] (PDF 114.3KB)
• Measurement Results [Fiscal Year 31 Implementation] (PDF 173.3KB)
• Measurement Results [Fiscal Year 2017-2018] (PDF 262.3KB)
• Measurement Results [Conducted in Heisei 27 and 28] (PDF 613.6KB)
• Measurement Results [Fiscal Year 2013-2014] (PDF 632.2KB)
• Measurement Results [Fiscal Year 2011-2012] (PDF 213.4KB)