Radiation Exposure at Locations Other Than the Afflicted Areas
Updated: July 20, 2011 17:00 (JST)Currently, as of July, the radioactive materials leakage from Fukushima Dai-chi
Nuclear Power Plant into the environment is yet to be brought to a definitive end.
However, the amount of the leakage has been drastically decreased.

The atmosphericconcentration in locations other than the afflicted area, (the cautionary zone of20-kilometer radius of the plant) is less than minimum detectable quantity.

Unlessvast amount of radioactive materials are released due to the deterioration of thereactors' conditions, we don't have to worry about the atmospheric concentration ofradioactive materials in such a distant locations.

Above-the-normal dose rate has been

observed in some areas not stricken by the disaster.

However, it mostly is due to thesurface-deposited radioactive cesium, and is not because of the radioactive materials
suspended in the air.
residence.

Therefore, opening windows does not affect the dose rate inside aAs searing summer nears, closing windows or wearing long-sleeved clothes,

which usually are preventative measures against atmospheric radioactive materials,
would not be the effective radiological protection.

In fact, it may work adversely, for it

could be the cause of heat disorder. For more details, please refer to the explanation
below.
The released radio-nuclides such as iodine (I) and cesium (Cs) have been generated by
nuclear fission during reactor operations.

The chain reaction of nuclear fission has

been stopped, and there has been no confirmation that a large amount of neutronradiation has been released.
Iodine is one of the halogens that may be easily turned into gaseous form at a hightemperature, which is why iodine is one of the elements easily released by a nuclear
accident. Moreover, cesium is one of the water-soluble alkali metals that may be easily
conveyed to the coolant water in which damaged fuel rods are immersed.

Also, it may

be easily released into the atmosphere in the form of mist.
The exposure to these radioisotopes, as widely reported by media, can be roughly
categorized into two types: external exposure and internal exposure. The former is theexposure to radiation from radioisotopes outside one’s body, and the latter is theFor inquiries, please contact: QandA@aesj.or.jp

exposure to radiation from radioisotopes that reside in internal organs and tissues
when ingested or inhaled.

As for the much-reported iodine and cesium, they arewater-soluble and thus may be easily removed by washing even when they come incontact with skin or clothes.

On the other hand, internal exposure means that one is atgreater risk of ionizing radiation for an extended period when the radioisotope remains
inside his/her body for a long period of time.
Meanwhile, the radioactive substance taken into a human body is tend to be distributed
tospecific organs and tissues depending on its physical and chemical properties, andis excreted by means of metabolism.

The iodine confirmed to have been flown from theafflicted areas has such characteristics that, while 70 % is not absorbed and excreted,
the remaining 30 % stays inside human body mainly in thyroid gland.

Effective halflife (the period of time in which the activity of a radioactive isotope decreases by half) isabout 7.5 days (Iodine-131).

The cesium, also confirmed to have been flown from thesite, may be absorbed into human body in the full amount and distributed throughout
the entire body muscles.
ICRP Pub.78).

Effective half-life is approximately 110 days (Cesium-137,

The amount of internal exposure to radioactive material lowers inaccordance with the effective half-life, and the effects of exposure may in turn lessen.
Even so, minimizing the intake of radioactive material is encouraged.

As preventative

measures, wearing a moist mask, washing hands, and avoiding direct exposure of skinwhenever leaving home, were all encouraged in the first few weeks after the outbreak ofaccident, where large amount of radioactive materials were released into theenvironment.
Radioisotope: a version of chemical element whose number of neutrons differs.

Theisotope may be either stable or unstable, and the unstable one emits radiation during its
decay to a stable form. The unstable isotope is called the radioisotope.
Effective Half Life: the period of time in which the activity of a radioactive isotope
decreases in a biological organism, resulting from a combination of radioactive decay
and biological excretion.

For inquiries, please contact: QandA@aesj.or.jp