In physics, the term radiation is generally used to indicate a set of phenomena characterized by the transport of energy in space. Typical examples of radiation are light and heat.

A feature common to almost all types of radiation (light, heat, etc..) Is the transfer of energy to matter. This "transfer" of energy can be explained simplistically, whereas the kinetic energy of the "particles" that make up its radiation (photons), the particle, once coming into contact with the material he can transfer the kinetic energy to subject, usually in the form of heat and light. A particular type of radiation consists of electromagnetic waves, characterized by a constant speed in a vacuum, finite, equal to about 299792 km / s (rounded value is often in the 3.0 x 108 m / s), denoted by c, by a particular frequency and its wavelength, indicated by the symbol λ (lambda). The frequency f is defined as the number of wavelengths that pass in a second for a given point in space, and it is possible to obtain numerically considering the following relationship:

This relationship is always valid because c is a constant. So the higher the value of the wave frequency the lower the wavelength of the same, then the speed of light is constant for any electromagnetic radiation that propagates in a vacuum. Light is electromagnetic radiation with wavelengths ranging from about 380 nm to about 760 nm violet red.

The absorption of energy by matter can cause a local increase in temperature, which is exploited in the case of solar heating by the light of the sun If the energy of the incident radiation on matter is sufficient to ionize the , is called ionizing radiation.

If the ionizing radiation involves a biological tissue can cause biological damage, acting on the DNA and prevents them from reproducing correctly. The supply of humans by ionizing radiation occurs through the external or internal. There is talk of external radiation exposure or when the source of radiation remains outside the human body, such as what happened to the liquidators of Chernobyl '. There is talk of internal exposure when the source of radiation is introduced into the human body, such as what happened to Alexander Litvinenko died that although chemical poisoning by Polonium has undergone a remarkable radiation of the same.

A source of atomic radiation resulting from the instability and / or nuclear elements. Elements in nature that this instability can be traced easily on the periodic table of elements, and in particular, are all elements that have atomic number (Z) equal to or more than 84 (Z> = 84), ie from polonium. There are also other isotopes of elements with atomic number less than that are radioactive and are produced by man, the most common case is produced by the 60Co 59Co nuclear reactor by the addition of a neutron. The 60Co, with a beta decay becomes 60Ni and emits two photons of energy 1.17 and 1.33 MeV, which are used in various fields such as medicine (cobalt bomb) or industrial (food processing, materials , sterilizations ...).

In general, the transformation of these elements into other elements is more stable by emitting α or β rays also accompanied by the emission of γ rays. The elements that have the characteristics that are called radioactive elements and the process of radiation is called radioactive decay.

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