The Alpha Particle, a positively charged nuclear particle, consists of two protons bound to two neutrons. Alpha particles are emitted spontaneously in some types of radioactive decay. They are also produced when Helium-4 atoms are completely ionised. Alpha particles are also known as Helium nuclei because of its chemical properties.

Because Alpha particles consist of neutrons and protons they can only be emitted from the nucleus of an atom (the nucleus consists only of protons and neutrons). Loss of an Alpha particle by a nucleus results in the formation of a new nucleus, lighter than the original by four mass units (the masses of the neutron and of the proton are about one unit each). An atom of the uranium isotope of mass 238, upon emitting an Alpha particle, becomes an atom of another element of mass 234.

Each of the two protons that form part of the Alpha particle emitted from an atom of uranium-238 possesses a unit of positive electric charge. Because the charge on the uranium-238 nucleus decreases by two units as a result of Alpha emission, the atomic number of the newly formed atom is 2 fewer than that of the original, which was 92. The new atom has an atomic number of 90 and hence is an isotope of the element Thorium.

⁹²₂₃₈U => ⁹⁰₂₃₄Th ₊ ²₄He

Usually very large (and heavy) nuclei emit Alpha particles spontaneously.

 

Radionuclides

The Alpha particles emitted from radionuclides have distinct energies. These energies, which are in the range of 4 MeV to 8 MeV, are not sufficient to enable Alpha particles to penetrate even the dead outer layer of the skin. Because of this they do not present an external radiation hazard and will therefore not penetrate the   human skin.

did you know?


alpha n.

the first letter of the Greek alphabet
(A, a)

related links


read about the beta particle
read about the gamma particle

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