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information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

No radiation level is safe

March 6, 2012

Health effects of radiation doses under 100 millisieverts still unknown



As radioactive material from the Fukushima No. 1 nuclear plant continues to contaminate wide swathes of Japan, the health effects of radiation -- including from relatively low doses -- are a matter of concern for many, and unknowns remain.

All matter is made of atoms, and the majority of it is stable. Some unstable matter, however, releases energy, or radiation, as its atoms change into other types of atoms. There are different types of radiation, like alpha rays, beta rays, gamma rays and x-rays, and they have the ability to pass through matter. The degree to which they can do this varies: alpha rays can be blocked with a single sheet of paper, while x-rays can pass through the human body. Even in the course of our daily lives, humans are naturally exposed to radiation. Japanese are exposed to an average of 1.5 millisieverts of radiation per year.

Radiation harms the body because it damages the DNA in its cells. DNA is an important substance that holds genetic information. If it is broken by the impact of radioactive rays or particles, mistakes can occur when it is repaired or the cell divides, leading to cell death or mutations and chromosomal abnormalities.

Radiation exposure includes external exposure from outside of the body, and internal exposure from taking in radioactive materials through food or water. Such materials that are ingested are expelled from the body through the metabolic process. In the case of cesium, this takes around 100 days.

Experts are divided over the difference in health effects of external and internal radiation exposure, but the International Commission on Radiological Protection (ICRP), which advises governments around the world, holds that both types of exposure are equal.

Long-term studies on around 93,000 people exposed to the Hiroshima and Nagasaki atomic bombings have shown that cancer rates rise proportionally with doses of 100 millisieverts or more. According to the National Institute of Radiological Sciences, exposure to 100 millisieverts of radiation leads to a 0.5 percent increase in the chances of dying of cancer.

Regarding the Fukushima nuclear disaster, many worry about "low radiation doses" of under 100 millisieverts, but science has not yet shown what the health effects of these dosages may be.

However, Yasuhito Sasaki, director at the Japan Radioisotope Association and former member of the ICRP, says, "There is no safe amount of radiation exposure. The less radiation one is exposed to, the better."

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