(Impact from outer space and the earth is also covered) What is natural radiation? (Vol. 1)

Hello, everyone. My name is Daichi, an expert providing the information about the radiation issues in an easy-to-understand manner.

It is a bit touched upon in this article, natural radiation exists around us all the time to make impact on us.

In this article, the amount of dose from natural radiation in Japan and around the world is summarized, followed by explanation in detail especially regarding impact caused by radiation from outer space, and from the earth.

In other words, this article will respond to the following questions:

-　How much impact is made on people in Japan and around the world from natural radiation?
-　What is radiation coming from outer space?
-　What is radiation coming from the earth?

Table of contents of this article

I have been involved with the radiation-relevant issues, like the policy on the decontamination activities and the management of the Interim Storage Facility, after the accident of the Fukushima Daiichi Nuclear Power Plant in 2011.

I received a doctorate in the field of radiation, while working in Fukushima.

(Impact from outer space and the earth is also covered) What is natural radiation? (Vol. 1)

First of all, overall impact from natural radiation is covered, followed by detailed explanation on impact caused especially by radiation from outer space and the earth.

Impact from natural radiation

This is also touched upon in this article, but let’s start from situation of dose caused by radiation in Japan and whole world, based on up-to-date data.

Impact on Japanese people

(Source: Created based on the UNSCEAR 2008 Report and the Radiation in the Living Environment (Calculation of Public Dose) 3rd Edition, Expanded Edition (2024) (The Nuclear Safety Research Association)

– Impact caused by radiation from outer space: 0.31mSv/y　
– Impact caused by radiation from the earth: 0.33mSv/y
– Impact caused by radiation emitted from radon and thoron: 0.47mSv/y
– Impact caused by radiation emitted from foods: 0.99mSv/y
– Medical exposure: 2.6mSv/y
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– Total: 4.7msV/y

For the next, let’s take a look at dose around the world.

Impact on people in the world

(Source: Created based on the UNSCEAR 2008 Report and the Radiation in the Living Environment (Calculation of Public Dose) 3rd Edition, Expanded Edition (2024) (The Nuclear Safety Research Association)

– Impact caused by radiation from outer space: 0.39mSv/y　
– Impact caused by radiation from the earth: 0.48mSv/y
– Impact caused by radiation emitted from radon and thoron: 1.26mSv/y
– Impact caused by radiation emitted from foods: 0.29mSv/y
– Medical exposure: 0.59mSv/y
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– Total: 3.0mSv/y

When comparing dose on people in Japan with dose on people in whole world, the most big difference can be seen in the medical exposure, although it is outside the scope of this article.

One of the reasons for the difference could be that people have a lot of opportunities to take medical radiation, because the number of equipment for CT scan per capita in Japan ranks top level in the world, and there is a culture to find something wrong for body at early stage.

I think that there are facts that in Japan each company is obliged to let employees take medical examination once a year, according to the Act on Labor Safety, and medical expense is comparatively less than other countries, due to insurance policy for all people.

I believe that the reasons behind for this include the fact that the Industrial Safety and Health Act requires each company to let employees undergo annual health checkups, and that the national health insurance system keeps medical costs relatively low compared to other countries.

Impact caused by radiation from outer space

Now mechanism etc. will be explained in detail for each item, regarding impact caused by natural radiation, except for medical exposure.

First of all, impact caused by radiation from outer space.

As a bit touched upon in this article, radiation named cosmic rays come from outer space on the Earth all the time.

Cosmic rays are particle beams with high energy, which rain down from the outer space, consisting of charged particles like protons and electrons.

These cosmic rays are blocked by magnetic field and atmosphere around the Earth, and would hardly reach the surface of the Earth directly, but they collide with nitrogen molecules and oxygen molecules in the air to create secondary cosmic rays like muons, neutrons and gamma rays, which reach the surface.

Impact caused by radiation from the earth

For the next, radiation emitted from the earth is here elaborated.

This is because radioactive materials were included in the materials from the beginning, which constituted the Earth, when the Earth was created 4.6 billion years ago.

Specifically, radioisotopes of uranium, thorium and potassium are representative examples, which were generated during supernova explosions.

Uranium and thorium have half-lives of approximately 4.5 billion and 14 billion years, respectively, and they are major sources of geothermal energy.

This means that we are exposed to radiation emitted by radioactive substances such as uranium and thorium, as well as radiation emitted by radium generated during the decay of uranium and thorium.

Regions with high natural radiation level in the world

The amount of natural radiation coming from the earth varies regions to regions, and in the world, there are regions, where the natural radiation level is much higher than the world average value of 0.48mSv/y as follows:

– Yangjiang (China): around 2.3mSv/y
– Orvie (Italy): around 3.4mSv/y
– Ramsar (Iran): around 4.7mSv/y
– Kerara (India): around 9.2mSv/y
– Araxá (Brazil): around 19.6mSv/y
Source: The UNSCEAR 2008 Report

This is largely due to the geology and mineral composition of the land that makes up the region.

Therefore, for example, areas with a lot of granite have higher levels of radiation, because granite contains relatively high amounts of uranium and thorium.

However, to date, even in the regions with high natural radiation level, so much increases have not been observed for incidence and mortality rates for cancer, compared with the regions with not so much high natural radiation.

This is because that, first, the dose itself is not the amount which causes negative impact on people’s body immediately, and secondly, when comparing the case of large exposure to radiation at once, with the case of small and gradual exposures to radiation, the latter makes less impact on people, even if the total amounts of radiation are same.

Summary

This time overall dose on people in Japan and around the world, and among them, radiation from outer space, and from the earth were explained.

In the next article, remaining points, that is, impact from breathing and from foods will be elaborated.

By the way, above-mentioned contents are summarized in the following videos.

– Japanese version

– English version

You can read the same article in Japanese here.

Thank you very much for reading this article.

See you next time!