Radioactivity

The cell is the basic unit of living systems, it is the elementary particle of life.
Each cell is in a fabric which itself is an organ that performs a function. The cell obeys a manufacturing plan contained in the molecule of deoxyribonucleic acid, or DNA, present in all living cells.
At the microscopic level, cells are composed of atoms in electromagnetic balance, it is what makes the matter remains coherent.
Radioactivity is a phenomenon that occurs in the nucleus of atoms deep.
Ionizing radiation Ionization is the act of removing or adding electrical loads to an atom. The atom that loses or wins loads, is more in balance electric it is called ion.  Ionizing radiation or radioactive, can tear off electrons from the biological material, if the energy of radioactive particles is greater than the binding energy of electrons. Dividing cells are most vulnerable to high radiation, for example, hematopoietic stem cells contained in the bone marrow that give rise to all blood cells.
To extract nuclear energy, engineers used a special radio-isotope, the nucleus of uranium 235, to break easily in its nucleus. Indeed its nucleus is unstable, it decays naturally, i.e. the cohesive force is not sufficient to hold the protons and neutrons.
Naturally it ejects particles and produces radioactive neutron radiation and energy. When a neutron is sent on a core of uranium 235, it makes it even more unstable it becomes fissile and breaks into two parts. This fission releases particles of ionizing radiation and high energy.

The "disintegration" (transformation of matter into energy), a radioactive nucleus such as uranium, causes the emission of high energy radiation.
These decays are accompanied by emission of gamma rays, whose wavelengths are shorter than those of X-rays, on the order of 10-9 meters, which makes it dangerous because it crosses the field.
Gamma rays produce damage similar to those produced by X-ray or ultraviolet (burns, cancer and genetic mutations).
Radioisotopes natural are, americium-241, antimony 125, carbon 14, cesium 134, 135 and 137, chlorine 36, cobalt 60, 242 and curium 244, iodine 129, 131 133, 85 and krypton-89, phosphorus 32, 239 and plutonium-241, polonium-210, potassium 40, radium 226 and 242, ruthenium 106, selenium 75, Sulphur 35, strontium-90, thorium 234, 3 tritium, uranium 235 and 238.

NB: The DNA, genetic information and heredity, produces occasional errors, most mistakes are bad, but sometimes these genetic mutations, produce beneficial effects, which allow the system to continue its evolution in an environment that is favorable...

If radioactivity is finely measure we will find everywhere, in a piece of wood, in minerals, in a block of granite and of course a piece of uranium. The main source of radioactivity is natural. It comes mainly from radon, a radioactive gas produced by the decay of uranium present in certain rocks such as granite.
We are exposed to radon, very variable, from 1 to 100 milli Sievert per year, it represents the largest share of human exposure, 42% of total exposure. In addition to building materials, plaster, brick, concrete, 0.1 to 1000 mSv / year. Cosmic rays are also a source of natural radiation, particularly at altitude. The dose is around 0.3 mSv / year, but it increases with air travel.
About 10% of the radiation received by a person from his own body, mainly due to the decay of carbon 14 and potassium 40. However, the main medical irradiation, received at radiographs. It represents about 50% of the average exposure to natural radiation.
During a medical scanner, the patient receives an average dose of 0.05 mSv for a local review, 25 mSv for a CT scan of the skull and 150 mSv for a whole body scanner. It is recommended not to exceed three per year exams body. Coal contains potassium, uranium and thorium, concentrated by a factor of 10 in the ashes, some of the radioactivity is found in the smoke and slightly increases the exposure of the order of micro-sievert year. In the early 20th century scientists did not understand radioactivity, but they already knew four radioactive elements uranium, thorium, radium and polonium. Radium has amazing natural properties, it produces heat spontaneously, it also produces a gas that was called at the time, the radium emanation, it makes the atmosphere electric and conductive discharge to remote condensers.

This is also the same principle of operation of the Geiger counter or Geiger-Müller. The Geiger counter, developed in 1928, used to measure a large number of radiation whose alpha, beta, gamma and X-ray Human activities, such as the impact of nuclear weapons testing, the impact of nuclear accidents, increase the annual dose to the world population. Earth, despite its magnetic shield, is continuously irradiated by a stream of particles, cosmic rays, high energy from outer space and the Sun. This cosmic radiation remains very low at sea level The radioactive dose rate is measured in Gy / h (gray per hour), formerly the rad / h (rad per hour). The equivalent dose is measured in Sv / h (sievert per hour).
The French nuclear sites are organized into zones corresponding to the doses. The Blue Zone (2.5 to 7.5 mSv / h), the green zone (7.5 to 25 mSv / h), the yellow zone (25 mSv / h 2 mSv / h, the orange zone (2 to 100 mSv / h), the red zone (> 100 mSv / h). The natural environment emits radiation ranging from 0.2 mSv / h to 1 mSv / h.
The dose rate that produces hazardous biological effects is from 1 mSv / h, that is to say "yellow zone".

NB: the isotope 14 of carbon content in the air and living organisms, remains roughly constant over time. Only after the death of the organism, the concentration of C14, decreases in its tissues.
This property is used for dating the time of death if it does not exceed 50 000 years.

The radioactivity relates to the nuclei of the matter it is characterized by the spontaneous disintegration of atomic nuclei emitting one or several radiation alpha, beta-, beta+, gamma, and even neutrons emission. Ionizing radiation can remove electrons from the atoms of the matter through which they pass, it is this characteristic that they are dangerous to humans. But these rays are more or less piercing. The emission of alpha radiation can be easily stopped by a single sheet of paper. The emission of beta radiation can be stopped by a sheet of aluminum or glass plate. The emission of gamma and neutron emission is largely attenuated by a thick layer of concrete.
However, we can not speak of radioactivity without mentioning the works on radiation the German physicist Wilhelm Conrad Roentgen (1835-1923). Wilhelm Röntgen, as many physicists of the time, is passionate the cathode rays discovered by Hittorf in 1869. But the name Wilhelm Röntgen, is associated with his discovery of a new type of radiation it called the "X-ray". In 1895, he performed an experiment where he placed various objects between a photographic plate and the radiation source and finds that transparency is variable depending on the type of object.
The radiation through matter, all the more easily that it is sparse and thin. December 22, 1895, he "photograph" the hand of his wife Anna Bertha Ludwig where the bones of the hand and its alliance are visible. The darkness around the bone, is the flesh of the hand x-rays through the skin much more easily than bone. This is the principle of radiography.
Wilhelm Röntgen was awarded the Nobel Prize in Physics in 1901.

Image: Photograph of the hand of Anna Bertha Ludwig Roentgen taken December 22, 1895 after a break of 20 minutes. The "Röntgen rays" through the matter all the more easily than it is sparse and thin. December 28, 1895, Röntgen published his discovery in an article entitled "Über eine neue Art von Strahlen" ("About a new kind of rays") in the bulletin of physicochemical Society Würzburg.