Radiation Measurement by Tokyo Metropolitan Government

The Tokyo Metropolitan Government conducted measurements of ambient radiation levels in Inagi City. The measurement results announced by the Tokyo Metropolitan Government are as follows.

Measurement Results

Measurement Location

Central Park General Ground

Measurement Date

June 15, 2011

Height (cm)	Dose Rate μSv/h (Micro Sieverts per hour)	Dose Rate Annual Equivalent Value mSv/y (millisieverts/year)(Note)
5	0.05	0.26
100	0.05	0.26

• Note: Based on the measured values, the estimated annual equivalent value was found to be below 1mSv per year, which is the indicator of the radiation dose received by the general public during normal times (excluding natural radiation, etc.) according to the recommendations of the International Commission on Radiological Protection (ICRP).
• Note: The conversion values include natural radiation levels, etc.

Measurement Overview

Measurement Date

June 15, 2011 (Wednesday)

Locations

Central Park General Ground (Surface Soil)

Measurement Height

Height of 5 centimeters and 100 centimeters from the ground surface

Measurer

Tokyo Metropolitan Government Employee (Health and Safety Research Center)

Measuring Equipment

Scintillation Survey Meter Hitachi Aloka Medical TCS166

Measurement Items

Ambient radiation level "0.05μGy/h (microgray/hour)"
Note: 1 gray of radiation in the atmosphere can be converted to 1 sievert.

Tokyo Metropolitan Institute of Public Health Website

• Related Reports on the Great East Japan Earthquake (Published tests conducted at the Health and Safety Research Center)(External Link)

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 "measurement results of ambient radiation levels in the city by Tokyo Metropolitan Government (0.05μSv/h: June 15, 2011)" under the condition that it continued for one year.

Annual Conversion Value Estimation Method (This is a simple calculation)

Annual conversion value mSv/y = (Measured value - Natural radiation level) × (8/24 [Time spent outdoors] + 16/24 [Time spent indoors] × 0.4 [Indoor radiation reduction rate]) × 365 days ÷ 1000 [Millisievert conversion]

⇒0.05μSv/h×(8/24+16/24×0.4)×365 days÷1000=0.2628mSv/y

• Note: This conversion value includes natural radiation levels.
  [Reference] The average natural radiation level in the country is said to be 0.05μSv/h.
• Note: Conditions
  • Assuming 8 hours outdoors and 16 hours indoors in a wooden house
  • Reduction effect (0.4) during stay in wooden house (16 hours)
• Note: The estimates are calculated based on the assumption that the same values will continue for one year from June 15, when measurements were taken in the city.

Glossary

• Sv (Sievert) - A unit that represents the body's effects of radiation
• mSv (millisievert) is a unit of one-thousandth of a sievert
• μSv (micro sievert) is a unit of one millionth of a sievert (one thousandth of a millisievert)

ICRP (International Commission on Radiological Protection) Standards

• Emergency: 20 to 100 mSv per year
• Annual 1 to 20 mSv during recovery after an emergency incident
• Normal times: less than 1mSv per year

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