Dr. Tsubokura's Radiation Lecture Vol.17

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

33. Radiation exposure in Eastern Japan is little different from that in Western Japan

It has been almost four and a half years since the Fukushima Daiichi nuclear accident (the publication date of the original article was August 23, 2015).

The air radiation dose rate has been gradually decreasing year by year; the air radiation dose rate in Soma City in 2015 fell by 70% compared to that of June 2011. However, the air dose rate will never reach zero due to the naturally occurring radiation emitted from radioactive agents in the universe or rocks and concrete in our living environment.

The level of naturally occurring radiation varies between regions in and outside of Japan. Initially, the region to the west of Fossa Magna—the north-south spot that geologically divides Japan in two—had a higher air radiation dose rate than the region to the east of Fossa Magna. One reason for this is that the distribution of granite (Kakougan) differs between the regions.Many places in Japan were contaminated with radioactive agents in the 2011 Fukushima nuclear disaster, and the air radiation dose rate increased after the nuclear accident in Fukushima.

A mountain of problems related to the contamination remain to be solved; however, fortunately, the amount of naturally occurring radiation varies between regions, and the level of contamination has been also gradually decreasing. Because of this, the difference in the levels of air radiation dose rates of the habitable areas of Fukushima and the Western region of Japan have been shrinking.

34. TDS (Time, Distance, Shielding) rule? The three principles of radiation protection

There are three ways to reduce external exposure received from radiation sources.

The first way is to shorten the time of exposure. When the duration of the exposure is halved, the dose of radiation exposure would be halved as well.

The second way is to increase the distance from a radiation source. The exposure dose is inversely proportional to the square of the distance from the source; this means that when the distance from the radiation source is doubled, the dose of radiation exposure will decrease by 1/4, and when the distance is tripled, the dose will be 1/9.

The third way is by placing shields between you and the radiation source. This also depends on the shape of the shields, but being inside a wooden house cuts the level of radiation exposure to 40% compared to the dose received outside.

Furthermore, the level of radiation is reduced to approximately 20% in a building block or a brick building.This principle is called the “Three Principles of Radiation Protection,” and these are effective ways to reduce levels of radiation exposure.

However, extreme protection interferes with daily life and may even harm your health more. Therefore, careful consideration is necessary for applying these principals to your life. ---------------------------------------------------------------------------------------------------------------------------------------

The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on August 23rd,30th 2015, and was reproduced for MRIC Global under the author's permission.