So, we know that exposing to enormously high radiation all at once or having accumulated over 100 millisieverts will increase the cancer risk. But what would happen if we were exposed to low radiation for a long period?
Nikkei newspaper of April 17 showed the above graph. The title is "The risk of cancer death based on an epidemiological research in the high radiation area in India."
I googled some erroneous spelling, but luckily, I found the following.
On the graph, the left vertical line shows risk, and in this case, the risk is set to 1. The bottom horizontal line shows the value in millisieverts. The longer they are exposed with low level of radiation, the risk is going down. Isn't that interesting? I heard some part of Brazil and Iran has high background radiation, so I guess the situation must be similar. In the above web article, I found the words, terrestrial gamma radiation. Terrestrial sounds mysterious. It reminds of Ashok's blog on Paspermia and Pansmeria. What we have under our lands are scary like faults, plates, and radioactive mineral but also fascinating.
According to Nikkei, in Karunagappally, Kerala, India, radioactive minerals are scattered in the area, and the average radiation there is 5 to 10 times more than the world average. The residents are exposed to the natural radiation of 10 to 20 millisieverts a year. In 2009, a study on 70,000 residents was conducted. The result was even the people who had accumulated over 600 millisieverts showed no evidence in the difference on risk when compared with a control group. For the same amount of radiation, if our exposure took a long period, then the effect on living thing would be smaller.