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[Kinds of Nuclei]
There occur 94 kinds of chemical elements naturally. The number of kinds of occurring elements is about one handred including artifitially produced ones. Then, is the number of kinds of nuclei equal to the number of kinds of elements? No, they are not equal, because there are several isotopes for one kind of element. An element is specified by its atomic number (= the charge of the nucleus). Accordingly, an element is sometimes a mixture of some isotopes with different masses; their nuclei contain different number of neutrons. Each isotope (or nucleus) is called nuclide.
The number of nuclides whose existences have currently been confirmed is about 3000, each of which is specified by its proton number Z (= the atomic number) and the neutron number N. Since the mass of a nuclide is almost proportional to the number A = Z + N, we call A the mass number.
To identify each nuclide, the following symbol is sometimes used:
where represents the chemical symbol (= the symbol of element).
For example, the nucleus of hydrogen atom; i.e. proton, is represented by , the nucleus of helium atom; i.e. alpha particle, is by , the nucleus of the most popular nitrogen is , and the most popular lead is shown by .
The chemical symbols are listed in the following table:
2-1-A: Table of Chemical Symbols
Each nuclide can be identified only by the chemical symbol and the mass number A. For a given chemical symbol, we can know the proton number Z referring to the Table of Chemical Symbols, and then the neutron number N = A - Z. Therefore, people sometimes use the following abbreviated form
For example, lead 208 is represented as .
Currently the existences of about 3000 nuclides have been confirmed experimentally. These nuclides are plotted on a graph called the Nuclear Chart as shown below.
In this chart, the abscissa shows the neutron number N, and the ordinate the proton number Z. The special numbers, 2, 8, 20,... on the abscissa and ordinate are the magic numbers which will be discussed later.
The whole graph is covered with fine meshes, where each mesh point (N,Z ) indicates one nuclide. A mesh corresponding to an occurring nuclide is shadowed. The darkness of the shadow depends on the life-time of the nuclide; the deeper the shadow, the longer the life time is. A black colored mesh implies a stable nucleus. (The part of the faintest shadow means unconfirmed but theoretically possible nuclides.) Looking at this Nuclear Chart, we can understand the (N,Z)-distribution of nuclides.
The above Nuclear Chart is taken from
For detail, please make an access to the original URL (address).
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