Alpha Decay

Alpha Decay

Alpha decay or α-decay is a type of radioactive decay in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom.

Alpha decay  occurs in very heavy elements like uranium, thorium and radium. The nuclei of these atoms have a lot more neutrons in their nuclei than protons, which makes these elements neutron rich. This richness makes alpha decay possible.

Alpha decay can be described like this:

1) The nucleus of these nucleus rich atom splits into two parts.

2) The alpha particle goes zooming off into space.

3) The nucleus left behind has its atomic number reduced by 2 and its mass number reduced by 4.

Gamow Theory of Alpha Decay

The Geiger–Nuttall law or Geiger–Nuttall rule relates the decay constant of a radioactive isotope with the energy of the alpha particles emitted. This relation also states that half-lives are exponentially dependent on decay energy, so that very large changes in half-life make comparatively small differences in decay energy, and thus alpha particle energy.

As per this rule, short-lived isotopes emit more energetic alpha particles than long-lived ones. This law was stated by Hans Geiger and John Mitchell Nuttall in the year 1911, hence the name was dedicated to these physicists.

Alpha Decay

Radioactive Decay

The spontaneous decay or breakdown of an atomic nucleus is known as Radioactive Decay. This decay in a nucleus causes release of energy and matter from the nucleus.

The most common forms of Radioactive decay are –

  1. Alpha Decay (Helium nucleus is emitted)
  2. Beta Decay (Electrons are emitted)
  3. Gamma Decay (High energy photons are emitted)

This is also termed as Nuclear Decay or Radioactivity. The element or isotope which emits radiation and undergoes the process of radioactivity is called Radioactive Element.


Practise This Question

A nucleus with mass number 220 initially at rest emits an α -particle. If the Q value of the reaction is 5.5 MeV. Calculate the kinetic energy of the α -particle