Measurement results of radiation doses in the air at 100 locations in Tokyo (June 2011)

The entire Tokyo area was zoned and, in principle, radiation doses in the air were measured at one location in each zone.

Measurement period The period from June 15, 2011 (Wed) to June 22, 2011 (Wed)
Details of measurement A Tokyo official takes measurements at 5 centimeters and 1 meter above the ground (soil)
Measurement method
Measuring instrument A Hitachi-Aloka Medical TCS166 scintillation-survey meter
Time constant 30 seconds
Measurement method Measurement is carried out 5 times and the average is calculated
Measurement locations 100

As a general rule, measurement locations, are locations desired by the respective municipalities, and, except for islands, measurements are carried out at one or more locations in each municipality.

Measurement results Measurement locations and measured values of radiation doses in the air
Measurement results measurement results here

Summary

The measurement 1 meter above ground was 0.03–0.20 μGy (microgray)/h; the measurement 5 centimeters above ground was 0.02–0.19 μGy (microgray)/h. These values, including the measured values from the measurements which have been carried out on the premises of the Tokyo Metropolitan Institute of Public Health, do not differ significantly from the values (0.04–0.21 μGy (microgray)/h) from information being provided by street monitors, etc. collected by the Metropolitan government.

The average of the measured values of measurements taken 1 meter above ground at 100 locations was 0.061 μGy (microgray)/h, and 0.067 μGy (microgray)/h for measurements taken 5 centimeters above ground, and these values were close to those measured by the monitoring posts set up at the Tokyo Metropolitan Institute of Public Health.

Measurements taken at 1 meter above ground and at 5 centimeters above ground indicated a tendency for the measured values at 5 centimeters above ground to be slightly higher. (Ref. 1)

As a trend within the Metropolitan area as a whole, it was observed that measured values were higher for the Eastern district than for other districts.

The highest value among the measurement results was 0.2 μGy (microgray)/h, and an estimate of the radiation dose received in one year, excluding the naturally-occurring radiation dose, etc., produces a tentative calculation of 0.79 mSv (millisieverts). (Ref. 2)

In the future, in response to request from municipalities, measurements will continue to be supported.

* A radiation doses in the air of 1 Gy (gray) can be converted to 1 Sv (sievert).

(Ref. 1)

In 49 locations, the measured values at 5 centimeters above ground were higher than the values for 1 meter above ground.

In 46 locations, the measured values at 5 centimeters above ground and 1 meter above ground were the same.

In 5 locations, the measured values at 1 meter above ground were higher than the values for 5 centimeters above ground.

(Ref. 2)

Tentatively calculated by converting 1 Gy (gray) into 1 Sv (sievert), subtracting the national average for natural radiation dosage of 0.05μSv/h (microsieverts per hour), and assuming 8 hours spent outside and 16 hours in a wooden house (reduction coefficient for a wooden house, 0.4)

(Ref. 3)

Measured values from the Institute of Public Health during the measurement period at 100 locations

Measurement
location
Dose rate
μGy/h (microgray/hour) *
Measurement
date
1m above ground Ground surface
(5cm above ground)
Monitoring post
(1.8m from the rooftop,
18m above ground)
Institute of Public Health 0.07 0.09 0.0592 June 15
Institute of Public Health 0.07 0.09 0.0590 June 16
Institute of Public Health 0.07 0.09 0.0625 June 17
Institute of Public Health 0.06 0.08 0.0585 June 18
Institute of Public Health 0.07 0.09 0.0587 June 19
Institute of Public Health 0.07 0.08 0.0589 June 20
Institute of Public Health 0.07 0.08 0.0587 June 21
Institute of Public Health 0.07 0.09 0.0601 June 22

* The time of measurement is from 8:00 am to 8:59 am, a radiation dose in the air of 1 gray can be converted to 1 sievert.