・ 100,000cpm (from the shoe of an evacuee at FUTABA evacuation center)
Assuming that this was measured by the GM survey meter commonly used for radiation measurement, the contamination level at the surface is 400 Bq/cm2.
Thecalculated values, however, would vary depending on the types of measuring instruments because of differences in detectable surface areas and device efficiencies.
If the nuclide was assumed to be iodine 131 and attached to the skin, the absorbed dose rate at the skin is as follows:
Since the conversion factor is 1319 ( nGy/h)/(Bq/cm2) for the skin surface (70 micro meter in depth), the absorbed dose rate results in 0.53 (mGy/h).This rate would even be smaller if decontamination procedure is performed on the skin.
The half life of iodine 131 is 8 days. The contamination is thought to be eliminated by taking a bath or naturally metabolized by the body. Therefore, 0.53 (mGy/h) does not pose any health hazard.
・ 1015 micro Sv ( μ Sv)is the air dose rate as of the afternoon of March 12th measured at the main gate of the Fukushima Nuclear Plant. If you stay there for one hour, your radiation dose is 1015 micro Sv ( μ Sv) or 1.015 milli Sv (mSv).
The radiation dose limit per year for the general public including nuclear power plants is regulated at 1 milli Sv/year.Going over this amount, however, does not necessarily lead to the development of negative health effects.
We are exposed to radiation in the natural environment at 2.4 milli Sv (mSv) in a year.There are some areas in the world with a high dose level such as 10 milli Sv (mSv) in the natural environment (See the illustration)
Dose Scale
description of the image
(narrator will read from the items which minimum scale of the dose have smaller value and will not make difference between Artificial radiation and Natural Background Radiation.)
Gy: Absorbed dose at each region
Sv(Sievert): unit of effective dose for protection against cancer or hereditary effects
Dental x-ray
0.01mSv
Annual dose target in the vicinity of light water nuclear power plant (The actual value is far below this number.)
0.05mSv
Chest X ray
Over 0.05mSv
Tokyo-NY (round trip) (increase in space radiation due to high altitude
Over 0.1mSv
Stomach X ray with Barium
Over 0.1mSv
Ramsal/Iran Natural background radiation (annual)
Over 0.1mSv and less than 1Sv
Annual dose limit for general public
1mSv
Natural background radiation per person (1.5mSv) Average in Japan.
Guarapari/Brazil Natural background radiation (annual)
Over 1mSv and less than 100mSv
Kerala/India Natural background radiation (annual)
Over 1mSv and less than 100mSv
Natural background radiation per person (2.4mSv) Average in the world
(0.4mSv from space, 0.5mSv from earth, 1.2mSv from radon, 0.3mSv from food)
Over 1mSv and less than 10mSv
PET examination
Over 1mSv and less than 10mSv
CT
Over 1mSv and less than 10mSv
Annual dose limit for radiation workers
10mSv
Excess cancer incidence is not observed in this range.
Less than 100mSv (100mGy)
Functional decline of the hematopoietic system
Over 100mGy and less than 1Gy
Lens opacity
Over 100mGy and less than 10Gy
Cardiac catheter (Skin dose)
Over 100mGy and less than 10Gy
Infertility
Over 1Gy and less than 10Gy
Temporary hair loss
Over 1Gy and less than 10Gy
Cataract
Over 1Gy and less than 10Gy
Cancer radiotherapy (dose only at the treated region)
Over 10Gy and less than 100Gy
References: UNACEAR 2000 Report, ICRP 2007 Recommendations.
Guideline for Medical Exposure
from the Japan Association of Radiological Technologists.