The atomic nuclei consisting of protons and neutrons are exposed to various transformations in nuclear reactions. The key difference of such reactions from chemical, mentioning only electrons consists in it. During disintegration the charge of a kernel and its mass number can change.
Chemical elements and their isotopes
According to modern chemical representations, the element is a type of atoms with the same charge of a kernel which is reflected in serial number of an element in D.I. Mendeleyev's table. Isotopes can differ in quantity of neutrons and, respectively, atomic mass, but as number of positively charged particles — protons — it is identical, important to understand that it is about the same element.
The proton has weight 1.0073 and. e. m (atomic units of mass) and charge +1. The electron charge is taken for unit of electric charge. The mass of an electroneutral neutron – 1.0087 and. e. m. To designate isotope, it is necessary to specify its atomic mass which consists of all protons and neutrons, and a kernel charge (number of protons or that the same, serial number). The atomic mass called also nucleon number or a nucleon is written down usually at the left from above from an element symbol, and serial number – at the left from below.
The similar form of record is used also for elementary particles. So, attribute to the β-beams which are representing electrons and having scornfully small weight a charge-1 (from below) and mass number 0 (from above). α-particles are positive two-charging ions of helium therefore they are designated by a He symbol with a charge of a kernel 2 and mass number 4. The relative mass of a proton of p and neutron of n is taken for 1, and their charges, respectively, are equal to 1 and 0. Isotopes of elements usually have no separate names. The exception makes only hydrogen: its isotope with mass number 1 is a protium, 2 – a deuterium, 3 – tritium. Introduction of special names is caused by the fact that hydrogen isotopes as much as possible differ from each other on weight.
Isotopes: stable and radioactive
Isotopes are stable and radioactive. The first are not exposed to disintegration therefore remain in the nature in original state. Examples of stable isotopes – oxygen with the atomic mass of 16, carbon with the atomic mass of 12, fluorine with the atomic mass of 19. The majority of natural elements are a mix of several stable isotopes.
Types of radioactive decay
The radioactive isotopes natural and artificial, spontaneously break up with emission α- or β-particles before formation of stable isotope. Speak about three types of spontaneous nuclear transformations: α-disintegration, β-disintegration and γ-disintegration. At α-disintegration the kernel lets out the α-particle consisting of two protons and two neutrons therefore the mass number of isotope decreases by 4, and a kernel charge – on 2. So, for example, radium breaks up to radon and an ion of helium: Ra(226, 88) →Rn(222, 86) +He(4, 2). In case of β-disintegration the neutron in an unstable kernel turns into a proton, and the kernel lets out a β-particle and an antineutrino. The mass number of isotope at the same time does not change, but the charge of a kernel increases on 1. At γ-disintegration the excited kernel lets out γ-radiation with small wavelength. Energy of a kernel at the same time decreases, but the charge of a kernel and mass number remain invariable.