Ionizing radiation is a common name for all subatomic particles (e.g. alpha, beta particles, gamma and X-rays, protons, neutrons, heavier nuclei,…) produced in nuclear reactions or by spontaneous nuclear decay, those energy is sufficient to strip away electrons from atoms in the process of direct or indirect ionization.

Biological effects

The biological effect of ionizing radiation and the response of human body depends on amount of absorbed radiation, on time during which the radiation has been absorbed, on type of radiation and on type and amount of tissue in which the radiation has been absorbed.

The human body is able to tolerate certain small amounts of radiation thanks to the natural repair process of cells in different tissues. With the increase of absorbed dose of ionizing radiation, the probability of harmful effects occurrence, which can lead to DNA damage and cells mutation, arises. Very high absorbed doses cause different diseases like skin erythema, infertility, blood forming deficiency, radiation sickness or even death.

Natural and man-made

The origin of ionizing radiation is natural or artificial (man-made). Even without human activities, we are exposed by ionizing radiation which value can vary widely.

One of sources of natural radiation are cosmic rays. The primary galactic and solar cosmic rays consist of high energetic protons (95%), alpha particles (4%) and heavier nuclei up to iron (1%). Due to interactions of primary cosmic rays with atomic nuclei of air in the atmosphere, cosmic showers arise.

Within these cascades different particles (protons, neutrons, electrons, positrons, muons, pions, kaons, gamma rays, neutrinos) are born in upper layers of atmosphere and some of them are able to reach the sea level or penetrate underground. In addition the cosmic rays produce cosmogenic radionuclides like 3H, 14C, 7Be, 10Be, 22Na which are spread by the atmospheric layers mixing.

The other source of natural radiation are radioactive nuclides naturally occurring in the environment, mainly in the earth crust. This are radionuclides which were born with other nuclides during the nucleosynthesis before our Earth was formed and those life-time is comparable to the age of the Earth, for example 238U, 232Th, 40K, 235U. Some of them are members of decay series and their progenies can penetrate from the earth crust to the atmosphere by means of different isotopes of radon.

The man-made sources of ionizing radiation are diverse from nuclear tests residues, nuclear accidents or nuclear power plant fuel cycle to medical diagnostics or nuclear medicine. The nuclear weapon testing in the atmosphere (most of them realized between 1945 and 1963 when a test ban treaty was signed) released great amounts of radioactive nuclides into the environment.

These artificial radionuclides were spread through the atmosphere worldwide and increased the level of background radiation for tens of years. Even during a standard operation of nuclear power reactor there is a great amount of different radioactive isotopes which are generated due to nuclear reactions between neutrons from the nuclear fuel and materials of the reactor active zone.

This is the fact which causes a potential danger from nuclear power plants and therefore their construction is designed so that the leakage of radioactive isotopes was minimized in case of an accident. In spite of the nuclear power plants design and its safety and security policy can’t prevent the consequences of unexpected natural disasters as we have seen for example in case of Fukushima Nuclear Power Plant.

Even if accidents like this occur very rarely, their consequences can be significant for general vicinity of the accident and identifiable all around the world.

All sources of ionizing radiation, whether naturals or man-made, should be monitored from the point of view of radiation safety, to minimize and prevent the unnecessary or accidental increase of the dose absorbed by population and individuals.