It was announced that the forest fire in Namie was reduced on May 6. Today, on May 7, we still do not have confirmation of the fire’s extinction. Meanwhile, surfing on the internet, we have noticed that many people were looking for radiation dose information, and relied on it for radioprotection.
Since we also received several questions and comments, we have decided to publish additional comments of M.Yoichi Ozawa of “Fukuichi (Fukushima Daiichi) Area Environmental Radiation Monitoring Project”, seen below.
In order to protect yourself from radiation, you must take into account both the radiation dose and the contamination. In the case of the radiation dose, you can imagine something like fixed paint. It requires radioprotection measures against external exposure. For example, in a high-dose place, you control the amount of exposure by staying a shorter period of time. The dose is expressed by units like Sv/h.
Contamination is like a floating powder, which can enter the body by breathing, eating and drinking, and cause internal irradiation. The radioprotection requires equipment such as clothes and masks. Contamination is taken into account in terms of the surface contamination density and the concentration of radioactive substances in the air.
The surface contamination density is the radioactivity per unit area, where radioactive materials are deposited or absorbed on the surface of the material. It is expressed by units such as Bq/cm2 and Bq/m2.
The concentration of radioactive material in the air is expressed by units such as Bq/cm3 or Bq/m3.
The following is a table in the radioprotection training textbook used in the crippled TEPCO Fukushima Daiichi nuclear power plant. The radioprotection is staged according to the classified areas. The lines in the table show the radiation dose, whereas the columns show contamination (in terms of the surface contamination density and the concentration of radioactive substances in the air). The combination gives 12 areas from 1A to 3D areas, and the radioprotection measures for workers are adapted accordingly.
For example, in the D areas workers are provided with a full mask and an oxygen cylinder.
Similarly, in the regions affected by the TEPCO Fukushima Daiichi nuclear power plant accident, we must consider the means of radioprotection by taking into account both the radiation dose and contamination.
In the case of environmental contamination, the air contamination density changes according to conditions such as fire, wind, and rain. Therefore, to protect ourselves, we need to monitor continuously not only during but also after the fire.
Furthermore, it has to be noted that monitoring post and air dust sampling show only gamma rays represented by cesium 137. Strontium 90 and plutonium 239 which emit beta and alpha rays that are most damaging in cases of internal irradiation are not measured. Aside from the question of the amount, these are certainly floating, and the risk of internal exposure cannot be ignored.
Please refer to the contamination map of the areas where the evacuation orders were lifted from last year to this year.
In light of this map and the TEPCO manual, you can see that there are many places in the area where you can return, and where you should wear heavy equipment with a full mask if you were a worker in a nuclear power plant.
In such an environment, ordinary people without a manual, nor professional radioprotection training are allowed to return, including babies and pregnant women.
In addition, whereas the workers are protected by the radiation protection standards shown in the table, in the context of minimization of the accident, residents are exposed to highly radio-contaminated environments without equipment.
If you think about it, it just does not make sense.