We are always surrounded by radiation. There is no place on the Earth where we can escape from it. We can’t see it or smell it; sometimes we can only feel its effect. Since its discovery in 1896, phenomenon of radioactivity and its impact on humans continues to be studied.

What is radiation?

Radiation is energy flow from the source. Nonionizing radiation doesn’t cause any changes in the structure of the atom it affects, but warms the material. It’s visible light, ultraviolet light, infrared light and microwave. Ionizing radiation disturbs the atoms of the substance; affects them enough to pull electrons out of their orbits.

Nonionizing radiation is hardly harmful and it only might cause issues to the people that work with source of it. However, the effects depend on the intensity, duration of exposure, environmental conditions and resistance of the organism and ability to adapt. Ionizing radiation can cause biological effect, that’s why it’s used in medicine, but also can be harmful as it provokes changes in composition of DNA.

What Are the Types of Ionizing Radiation?

Among ionizing radiation, we can distinguish alpha (α), beta (β), gamma (γ) and x-rays.

While alpha and beta are relatively heavy particles, gamma and x-rays are types of electromagnetic waves that can ionize biological material.

α-radiation is a stream of positively charged particles moving at a speed of about 20,000 km/sec. These particles don’t travel far, only 11 cm in the air and a few microns in human soft tissues. In terms of physics, they are heavy and big, that’s why they can hardly penetrate human skin and can be stopped even by a sheet of paper. However, they cause danger if they’re in the human body. They can be inhaled, swallowed or get to the blood through wounds.

β-radiation is a stream of negatively charged particles. Their speed is close to the speed of light; however, different particles have different energy. So, they cover different distances: from 1 cm to a couple of meters. In comparison to alpha, the intensity of the effect of beta particles on human tissues is hundreds times less. Although, beta can penetrate body tissues deeper: by 1-2 cm. The best and simplest protection from it is our clothes.

γ-radiation is a short-wave electromagnetic radiation. Like beta’s, its speed is close to the light’s. There is almost no obstacle for gamma rays: they can get to human organs and go through them. Gamma can be weakened, but not stopped completely, by houses’ walls and metal constructions.

X-rays are similar to γ-waves, but with less speed and energy. It’s penetrating electromagnetic irradiation formed due to acceleration of electrons to high speed and their abrupt stop in a collision with a solid body or movements in the inner orbits of some atoms.

What Are Harmful and Safe Radioactive Levels?

Radiation exposure can be short-term and long term.

Starting from 1 Sv/h, short-term exposure is already dangerous for people. When receiving a dose of 500 mSv, there is a noticeable change in somatics. Absorbing 1 Sv leads to the first stage of acute radiation disease.

However, this dose is not lethal. Dose of 2 Sv causes disorders of the digestive systems, headache and mild lesions of the mucous membrane. However, more than 4 Sv absorbed in a short time are lethal for a human being. This amount of radiation causes changes in blood structure, tissue destruction and deterioration of bones.

When it comes to long-term exposure and low levels, the line between dangerous levels and safe is very thin. In this case, it’s difficult to say equivocally, how many microsieverts or rads per hour is safe. When living with level of 0,6-1,2 μSv/h, people are at risk. Only radiation will not be fatal, but along with hereditary diseases, lifestyle and quality of the environment can lead to cancer. Levels higher than 1,2 μSv/h are dangerous for permanent living, because in this case annual dose for a person might be more than 10 mSv; that increases risks of cancer significantly.

All in all, less than 0.6 μSv/h or 60 microroentgens per hour are safe for people. Double of this level might be dangerous.

Are We Free From Danger Living With a Natural Background?

Natural background is made by space sources (sun, for example) and Earth-specific radionuclides. Human beings are always affected by radiation from space, radionuclides that are present in the ground and the ones we get from air, food and water. Level of natural background varies in different places of the Earth. For example, in the majority of European countries normal level fluctuates within 0,2-0,5 μSv/h (microsievert per hour) which is equal to 20 μR/h (microroentgen per hour). It also depends on the altitude. In the highland areas the level can reach 0,8 μSv/h (80 μR/h).

The radiation is everywhere. There is no place on the Earth where we can escape from it. According to the UN Scientific Committee on the Effects of Atomic Radiation, 2,4 mSv is an average annual dose from natural sources. Moreover, we add some annual 2,5 – 3 mSv more because of man-made background. First of all, it’s about medicine. Simple X-ray of our chest gives us 600 μSv/h. During one hour on a plane we receive around 3 μSv. Radioactive polonium-210 and lead-210 are found in tobacco. So, smokers receive additional 250 μSv/y (average).

How Can We Protect Ourselves?

The natural background is completely safe for the people. If the population lives on the area which wasn’t affected by any nuclear disasters, there is no need to worry about water and products we consume. For example, on the areas affected by Chernobyl accident people are not recommended gathering and consuming mushrooms: they absorb radioactive cesium-137. Also, medical X-ray should be done only when necessary. It’s not recommended having it more often than 2 times per year. When working with sources of radiation, people should consider time and distance: the less time they spend by the source and the more distance they keep the more secure they are.

Resources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2672370/
https://www.dhs.gov/sites/default/files/publications/Quick%20Reference%20Guide%20Final.pdf
https://www.stuk.fi/web/ru/radiacionnaya-opasnost/primery-doz-oblucenia
https://www.unscear.org/unscear/publications.html
http://ecotest.ua/press/blog/what-is-radiation/