5.Explain the meaning of the numerical values reported by the media 

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)

 Image DoseScale 

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.