Measurement results of radiation levels in the city

In response to the Great East Japan Earthquake, the city has been conducting fixed-point measurements of air radiation levels at 5cm and 100cm above the ground at elementary and junior high schools, nursery schools, and kindergartens since June 2011, but currently. The measured value of the radiation monitoring post in Shinjuku Ward, which had been set up before the Great East Japan Earthquake in Tokyo, is lower than the standard value set by the Ministry of the Environment (0.23 microsieverts per hour). Due to reasons such as the fact that the radiation level has decreased to a low level, we will suspend measurement of air radiation levels in the city from 2021 onwards. However, if any concerns arise, measurements will be resumed immediately.

Please see the link below for more information.

Please check the link below for the results of Shinjuku Ward's monitoring post.

After changing the measurement frequency, we have measured the air radiation dose in the city, and we would like to publish the results.

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

Note: The annual equivalent of 0.23 microsieverts per hour is 0.99864 millisieverts, and according to the recommendations of the International Commission on Radiological Protection (ICRP), it is an indicator of the normal radiation dose received by the general public (less than 1 millisievert per year (natural radiation)). This value is used as the city's criterion value, but when the annualized value was calculated based on the measured value, it was less than 0.526 millisievert per year (including natural radiation dose, etc.). , the value was less than 1 millisievert per year (excluding natural radiation levels, etc.).

○Measurement locations Municipal elementary and junior high schools, municipal/private nursery schools, private kindergartens

○Measurement point Schoolyard or kindergarten ○Measurement height: 5 cm and 100 cm from the ground surface

○Measurement by city employee

○Measuring equipment・PA-1000 (elementary school/junior high school)

・TCS-172B (nursery school/kindergarten)
Note: The number of decimal places for the measured value varies depending on the measuring device used. (PA-1000 displays 3 decimal places, TCS-172B displays 2 decimal places.)
For your reference: The Tokyo Metropolitan Government's Public Health, Safety and Wellness Center is comparing measurements taken using multiple measuring devices.
For more information, please see "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 unit: microsievert per hour

○About future measurements

• The first measurement conducted on June 28, 2011 revealed that there were no significant changes in the values ​​due to height, so subsequent measurements were conducted at 5 cm and 100 cm above the ground.

Regarding the annualized estimate of the air radiation dose in the city, we made a trial calculation under the condition that the "air radiation dose measurement results in the city" continued for one year.

○Annualized value estimation method Annualized value (millisieverts each year) = (measured value - natural radiation dose) x (8/24 [time outdoors] + 16/24 [time indoors] x 0.4 [indoors Radiation reduction rate]) x 24 hours x 365 days ÷ 1000 [millimeter conversion]

<In the case of 0.090 microsieverts per hour>
⇒0.090 x (8/24 [time outdoors] + 16/24 [time indoors] x 0.4 [reduction rate of radiation indoors]) x 24 hours x 365 days ÷ 1000 ≒ 0.473 millisieverts per year Note: This conversion value does not subtract natural radiation amounts.
[Reference] The average natural radiation dose in Japan 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 on staying indoors in a wooden house (16 hours) (coefficient 0.4)

Note: Estimates are based on the assumption that the measured values ​​at the locations where measurements were taken this time continue for one year.

○ Terminology Sievert (Sv) Unit expressing the physical effects of radiation Millisievert (mSv) Unit 1/1,000 of a sievert Microsievert (μSv) 1/1,000,000 of a sievert (1,000 of a millisievert) 1) Unit of

○ICRP (International Commission on Radiological Protection) standards
During an emergency: 20 mSv to 100 mSv per year During recovery after an emergency accident: 1 mSv to 20 mSv per year Normal times: 1 mSv or less per year

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