The term "radiation" describes the diffusion of energy within a space either in the form of particles (electrons for example) or in the form of waves (radio waves for example).
Radiation is part of our live, as we are surrounded by a vast volume of natural and artificial sources of radiation. Through our senses, we can understand a tiny area of the radiation spectrum: visible light though our eyes and ultraviolet radiation through heat. Their existence has become more perceivable during the last century, as a result of the development of technical means for their detection.
Natural radiation sources are the natural radioisotopes found in the soil, subsoil, air, water and they are there since the very first moment that the earth was created. The sun is also a natural source of radiation; so is the cosmic radiation emitted by celestial bodies.
Artificial sources of radiation are the devices which generate radiation, such as the equipment used in medical applications, lamps, radars, antennas, etc.
Radiation is characterized by its wave length or its frequency and the energy it bears. Depending on such energy and its impact to the matter, radiation is classified into two big categories: ionizing radiation and non-ionizing radiation.
Ionizing radiation is the one whose energy renders it able to penetrate to the matter and causes the ionization of its atoms. X rays, gamma rays, electrons, protons and neutrons are forms of ionizing radiation.
Non-ionizing radiation is the one which bears rather low energy that cannot cause ionization of the matter. However, the energy carried by non-ionizing radiation is capable of causing electric, chemical and thermal impact to the matter. Non-ionizing radiation covers the spectrum from low-frequency electric and magnetic fields to ultraviolent radiation.
The impact of radiation to human organization is complicated, sometimes favorable sometimes adverse, depending on the kind, the volume and the energy it carries.