You can calculate it to a certain degree, though it is slightly complex.
First, you can find an amount of radiation received from radioactive substances in the air by adding all the figures announced by the MEXT for a period from the day of the accident to the present.The following is the calculation of the radiation dose in Tokyo mentioned in Question 3.
Example: Calculation of radiation exposure in reference to the announced air doses
The air dose was 0.0927 micro Sv/h on average according to the MEXT’s data (for 29 days from March 14 - April 11)
0.0927 x 24 hours x 29 days = 64.5 micro Sv ----- (1)
The average air dose in Tokyo in normal times is 0.028-0.079 micro Sv/h, so the median value 0.0535 is used as follows.
0.0535 x 24 hours x 29 days = 37.2 micro Sv ------ (2)
(1) - (2) = 27.3 ----- (3)
If you go out for 8 hours and stay indoors for 16 hours, the reduction coefficient is:
1 x 8/24+0.4 x 16/24 = 0.6---- (4)
The dose of radiation received is:
(3) x (4) = 27.3 x 0.6 = 16.38 ≒ 16 micro Sv.
Example: Calculation of exposure dose from radioactive substances occurring in food and water
The exposure dose from radioactive substances in water or food (including potential exposure from radioactive substances ingested into the body) can be estimated by the following formula.
Dose of radiation received (micro Sv) = Effective dose coefficient (the values given in the chart below) x radioactive concentration (Bq/kg) x food intake (kg)
Effective dose coefficients(micro Sv/Bq)
|
Iodine-131 |
Cesium-137 |
Cesium-134 |
New-born baby (3 months) |
0.18 |
0.020 |
0.026 |
Infant(Age 1) |
0.18 |
0.012 |
0.016 |
Child(Age 2-7) |
0.10 |
0.0096 |
0.013 |
Adult |
0.022 |
0.013 |
0.019 |
※ (Oral ingestion; NIRS compiled the data based on “ICRP Database of Dose Coefficients: Workers and Members of the public, CD-ROM, 1998”)
Suppose 1kg of water contains 8.59Bq iodine-131, 0.45Bq Cesium-137 and 0.28Bq Cesium-134.If an adult drinks 1.65 liter of water a day for 29 days, the radiation exposure doses will be:
Iodine-131: 0.022 x 8.59 x 1.65 x 29 = 9.0 micro Sv.---(1)
Cesium-137: 0.013 x 0.45 x 1.65 x 29 = 0.28 micro Sv----(2)
Cesium-134: 0.019 x 0.28 x 1.65 x 29 = 0.25 micro Sv----(3)
Exposure dose = (1) + (2) + (3) = 9.53=about 10 micro Sv.
※ The average of the data announced by the Tokyo Metropolitan Government from March 18 to April 11.
The estimate given above in (3) uses values close to the average of the results of radiation tests on distributed foods (11 samples of milk, 241 samples of vegetables and 5 samples of fish) presented by the Ministry of Health from March 19 to April 11.When a total of Cesium isotopes 134 and 137 combined is given, the ratio of the two substances is assumed to be 1 to 1.