Dr. Tsubokura's Radiation Lecture Vol.6

Author: Masaharu Tsubokura

Editors: Mariko Irie, Izumi Yoshida, Yuki Senoo

11.An examination of “additional” radiation exposure

External radiation exposure is the type of the exposure which occurs when you are exposed to radiation originating outside of the human body. On the other hand, internal exposure is caused by the radioactive substances taken into our body.

In our daily life, internal exposure occurs when we inhale radioactive radon in the air and intake radioactive potassium through our diet. By contrast, external exposure is caused by radiation which is released from the universe and the soil. As I previously explained, their amount is not constrained, but distribution can be diverse, depending on the geographical location.

It should be noted that neither cumulative dosimeters (glass dosimeters), which are designed to detect external exposure, nor Whole-Body Counters, which are designed to identify internal exposure, aim to inspect whether we had experienced radiation exposure “for the first time in our lives" following the 2011 nuclear power plant accident. Instead, these devices aim to investigate how much "extra" radiation exposure caused by the radioactive agents newly disseminated by the disaster as well as those which had originally existed.

12)An examination to recognize the current amount of radiation exposure

External and internal radiation exposure can be assessed with the devices specialized in such measurements. It should be noted that those devices are not capable of measuring the level of the entire exposure which we have experienced "in our whole lives." Instead, they can be used to evaluate the level of radiation exposure we "currently" experience.

Glass dosimeters can determine the level of external radiation exposure during the previous two to three months, while Whole-Body Counters can detect the amount of radioactive cesium in our bodies at the time of the measurement.

This information is quite valuable to us. For example, we can estimate the annual level of external radiation exposure from the value detected by measurement by grass dosimeters. Moreover, the negative results in the Whole-Body Counters suggest that the daily intake of radioactive agents in our daily life may be negligible.

Then, how can we know the level of the potential radiation exposure experienced immediately following the 2011 nuclear power plant accident? Here, two measures could be applied to attain this.

One is to refer to the examinations undertaken at the very early stage after the disaster, and the other is to perform a computer simulation to estimate the dynamics of radioactive substances in the immediate aftermath of the accident, using the historical trend of the air dose rate and radioactive substances after the disaster.

----------------------------------------------------------------------------------------------------------------------The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on March 22nd and 29th 2015,and was reproduced for MRIC Global under the author's permission.