FAQs: Japan nuclear concerns
1. What is the current risk of radiation-related health problems in Japan to those near the reactor at the time, and those in other parts of Japan?
The actions proposed by the Government of Japan are in line with the existing recommendations based on public health expertise. The government is asking people living within 20km of the Fukushima Daiichi nuclear power plant to evacuate and those between 20 km and 30 km away from the plant are asked to stay indoors in unventilated
rooms. People living farther away are at lower risk than those who live nearby.
can change if there are further incidents at these plants and WHO is following the situation closely. However, radiation-related health consequences will depend on exposure
. Exposure in turn is dependent on the amount of radiation released from the reactor, weather conditions such as wind and rain at the time of the explosion, the distance someone is from the plant, and the amount of time someone is in irradiated areas.
When certain atoms disintegrate, either naturally or in man made situations, they release a type of energy called Ionizing radiation (IR). This energy can travel as either electromagnetic
waves (gamma or X-rays) or as particles (neutrons, beta or alpha).
The time required for the energy released by a radionuclide to decrease by half (i.e., the "half-life") range from tiny fractions of a second to millions of years depending on the type of atoms.
3. Are people normally exposed to ionizing radiation?
Human beings are exposed to natural radiation on a daily basis. The radiation comes from space (cosmic rays) as well as natural radioactive
materials found in the soil, water and air. Radon gas is a naturally formed gas that is the main natural source of radiation.
People can also be exposed to radiation from human-made sources. Today, the most common man made source of ionizing radiation are certain medical devices such as X-ray machines.
The radiation dose can be expressed in units of Sievert (Sv). On average, a person is exposed to approximately 3.0 mSv/year of which, 80% (2.4 mSv) is due to naturally-occurring sources (i.e., background radiation), 19.6 % (almost 0.6 mSv) is due to the medical use of radiation and the remaining 0.4% (around 0.01 mSv) is due to other sources of human-made radiation.
In some parts of the world, levels of exposure to natural radiation differ due to differences in the local geology. People in some areas can be exposed to more than 200 times
the global average.
4. How are people exposed to ionizing radiation?
Ionizing radiation may result from sources outside or inside of the body (i.e. external irradiation
or internal contamination
Internal contamination may result from breathing in or swallowing radioactive material or through contamination of wounds.
External irradiation is produced when a person is exposed to external sources such as X-rays or when radioactive material (e.g. dust, liquid, aerosols) becomes attached to skin or clothes, resulting in external contamination.
External contamination can often be washed off the body.