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Avogadro’s Number



The actors of the play are as small as they are numerous

Méditerranée et nombre d'Avogadro
Le soleil se couche sur le cap Sounion, en Grèce. Le nombre de gouttes d'eau dans la baie est déjà grand, mais il faudrait passer à l'échelle de la Méditerranée pour qu'il puisse être comparé au nombre d'Avogadro. En regard de ce chiffre, un 6 suivi de 23 zéros, même la descendance aussi nombreuse que les grains de sables de la plage promise à Abraham, reste toute petite.
G.Edelheit

The microscopic size of atoms is made up for by their extreme abundance. In one cubic centimetre of water there are as many atoms of oxygen and hydrogen as there are molecules of water in the Mediterranean. Examining the atom is like going from the scale of the Mediterranean to that of a drop of water.

The large quantity of atoms is indicated by the value of Avogadro’s number. This number, which represents the number of water molecules in 18g of water, or the number of iron atoms in 56g of iron, has a value of N=6.022 x 10^23 – 602 thousand billion billion. The number of atoms in the human body is about 10,000 times higher than this. These immensely high numbers must be borne in mind when thinking about the atomic world. They help explain why, in a radioactive body, the number of nuclei decaying per second is high while in the same time the ratio of nuclei decaying is infinitesimally small.

Avogadro's number
Avogadro's number is the number of atoms (donc de noyaux) within an atom-gram (A) of a given atomic kind. Because of its extremely high value, the number of atoms (n) within a sample of mass (m) remains always very high. In the formula abose the atomic number A is also the number of protons and neutrobs of the considered atomn. Amédéo Avogadro (1776-1856) was an italian physicist and chemist.
IN2P3
Modern detectors of radioactivity are able to detect the radiations emitted during the decay of an individual atom. This allows ultra-sensitive dectectors to count the decays of atomic nuclei ! As any sample of matter contains innumerable multidudes of atoms, physicists, scientists or doctors can observe fairly large numbers of radiations -emitted even by trace amounts of radioactive species.

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