The ionizing radiations such as α, β, and γ except neutron are originated from unstable nuclei of an atom in an element undergoing radioactive decay.
Some naturally occurring heavy nuclei with atomic number 82 < Z < 92 and artificially produced transuranic element Z > 92 decay by alpha emission, in which the parent nucleus loses both mass and charge. The alpha particle is emitted in preference to other light particles such as deuteron (2H), tritium (3H), and helium (3He). Because energy must be released in order for decay to take place at all. The alpha particle has very stable and high binding energy, has tightly bound structure, and can be emitted spontaneously with positive energy in alpha decay, whereas 2H, 3H, and 3He decay would require an input energy. The parent nucleus (Z, A) is transformed XZA→XZ−2A−4+αXZA→XZ−2A−4+αE1
It has less penetrating and high ionizing power.
Beta particles are fast electron or positron; these are originated from weak interaction decay of a neutron or proton in nuclei, which contains an excess of the respective nucleon. In a neutron-rich nucleus, neutron can transform itself in to a proton by emission of beta particles and antineutrino. Similarly, in the nuclei with rich proton, it transforms into neutron by emission of neutrino and positron. These radiations are high penetrating and less ionizing power:
n → p + e− + ν− E2
Similarly in the nuclei with rich proton, the decay is
p → n + e+ + E3
The emission of gamma rays is usually the most common mode of nuclear excitation and also occurs through internal conversion.
X-rays arises from the electron cloud surrounding the nucleus. They were discovered by Roentgen in 1895. X-rays are produced in X-ray tube by fast moving electron which is suddenly stopped by target.
It is a neutral particle that produces ionization indirectly by emission of γ-rays and charged particles when interacting with matter. These charged particles produce the ionization. It has more penetrating than gamma ray and can be stopped by thin concrete or paraffin barrier. They are produced by nuclear reaction and spontaneous fission in nuclear reactors. The characteristic emission of α, β, γ, and neutron sources is given in Table.
7.4 × 103 years
2.4 × 104 years
3.08 × 105 years
|8 × 105 years|
2 k.6 years
|Source||Half-life||Energy MeV||Yield × 106|
Characteristics of some α, β, and γ emitters and neutron (sources).