Characteristics of α-radiation, β-radiation and γ-radiation

September 23, 2020

A) α-radiation

The α-rays are not rays, but consist of a stream of positively charged particles, having 2 units of positive (+) charge, and 4 units of mass. Thus, α-particles are doubly ionized helium atoms i.e., He²⁺.
The α-particles emitted by any radioactive source are shot out with high velocity. The initial velocity depends on the nature of the radioactive element. Most of the α-particles are found to have velocities lying between 1.5 to 2 × 10⁷ m/s. This velocity is thus one-fifteenth to one-twentieth that of light.
The range of α-particles is the distance from its source which the particles travel before cease to have any appreciable power of causing ionization. The range of α-particles is small. Usually, the range of α-particles is 2-10cm.
The α-particles can penetrate thin sheets (<0.1mm thickness) of aluminium and mica, etc.
The α-particles ionize the gas through which they pass.
They cause luminescence on striking a zinc sulphide screen.

Image source: slideplayer

Β) β-radiation

Deflection under magnetic and electric fields showed that β-rays consist of negatively charged particles.
They have the same value of e/m as shown by the cathode rays. Thus, β-particles are electrons.
β -particles travel at a very high speed, the average velocity being ten times that of the alpha particles, i.e., of the order of about 1.5 to 2 ×10⁸m/s.
These particles cause ionization of the gases through which they pass. The ionizing power of β –particles is much less than that of alpha particles.
Because of their small size and light mass, the β-particles are more penetrating than alpha particles. In air, the β-particles can penetrate up-to a distance of few metres. These particles can however, be stopped by about 1 cm thick aluminium sheets.
Due to low kinetic energy, these particles have less effect on ZnS screen.
The photographic activity of these particles is greater than that of alpha particles. This is perhaps due to the production of X-rays on the interaction of β-particles with the matter.

C) γ-radiation

The emission of alpha and beta particle due to the disintegration of any nucleus is generally, accompanied by the emission of gamma (γ) radiation.
The γ-rays are produced when the excited nuclei, left after alpha or beta emission, return to the ground or any other lower energy state.
These radiations are similar to the X-rays, except that they have extremely short wavelength viz., 10^-10 to 10^–13
These are short wavelength electromagnetic radiation similar to the light. These ray have no mass, hence cannot be considered as particles. Since, these do not carry any charge, hence are not affected by the electric and magnetic fields.
These travel with the speed of light.
Due to their short wavelength, γ-rays have much higher penetrating power than alpha or beta radiations. These can penetrate through a 100cm thick aluminium sheet.
The ionization ability of γ-rays is very poor.