Measurement of radiation dose by the Tokyo Metropolitan Government

　The Tokyo Metropolitan Government conducted air radiation dose measurements in Inagi City. The measurement results announced by the Tokyo Metropolitan Government are as follows.

Note: When the annualized value was estimated based on the measured values, it was 1 mSv per year, which is an indicator of the normal radiation dose received by the general public (excluding natural radiation dose, etc.) according to the recommendations of the International Commission on Radiological Protection (ICRP). The values ​​are as follows.
Note: Converted values ​​include natural radiation doses, etc.

○Measurement date: Wednesday, June 15, 2011

○Location: Central Park General Ground (Soil surface)

○Measurement height: 5 cm and 100 cm from the ground surface

○Measuring person: Tokyo Metropolitan Government employee (Health and Safety Research Center)

○Measuring equipment Scintillation type survey meter Hitachi Aloka Medical TCS166

○Measurement item Air radiation dose "0.05μGy/h (microgray/hour)"
Note: 1 Gy of radiation in the atmosphere can be converted to 1 Sievert.

○Tokyo Metropolitan Health and Safety Research Center homepage related to the Great East Japan Earthquake (related tests conducted by the Health and Safety Research Center are posted) (external link)

　Regarding the estimation of the annual equivalent value of the air radiation dose in the city, the trial calculation was made under the condition that the "measurement results of the air radiation dose in the city by the Tokyo Metropolitan Government (0.05μSv/h: June 15, 2011)" continued for one year. did.

○Annualized value estimation method (simple trial calculation)
Annualized value mSv/y = (measured value - natural radiation dose) x (8/24 [time outdoors] + 16/24 [time indoors] x 0.4 [indoor radiation reduction rate]) x 365 days ÷1000 [millimeter conversion]

⇒0.05μSv/h × (8/24 + 16/24 × 0.4) × 365 days ÷ 1000 = 0.2628mSv/y
Note: This converted value includes natural radiation dose.
[Reference] The average natural radiation dose in Japan is said to be 0.05μSv/h

Note: Condition

• Assuming 8 hours outdoors and 16 hours indoors
• Reduction effect (0.4) on staying indoors in a wooden house (16 hours)
  

Note: Estimates are based on the assumption that the same values ​​continue for one year from June 15th, when measurements were taken in the city.

○Term explanation
Sv (sievert) A unit that expresses the effects of radiation on the body
mSv (millisievert) A unit of 1/1,000 of a sievert μSv (microsievert) A unit of 1/1,000,000 of a sievert (1/1,000 of a millisievert)

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

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