Basics of Radioactivity

Basics of Radioactivity

This article deals with ‘Basics of Radioactivity .’ This is part of our series on ‘Science and Technology’ which is an important pillar of the GS-3 syllabus. For more articles, you can click here.

Constituents of Atom

Atom has the following three constituents

Particle Mass (Kg) Charge (Coulomb)
Proton 1.672 X 10^-27 + 1.6 X 10^ -19
Neutron 1.675 X 10^-27 Neutral
Electron 9.108 X 10^-31 1.6 X 10^-19

Mass of Proton almost = Mass of Neutron = 1830 X Mass of Electron.

Atomic Structure

  • In an atom, Central Nucleus is surrounded by electrons at various energy levels. 
  • The most successful model is Wave Mechanical Model, but that is a mathematical rather than a visual model.
  • For our purpose, Bohr Atomic Model is enough. 

Bohr Atomic Model

  • Atom consists of 
    • Central Nucleus: Containing all Protons & Neutrons with almost the whole mass concentrated here. 
    • Electrons: Revolves around the nucleus in a circular pattern (like planets around the sun) 
  • Electrons can revolve only in certain specified orbits, with the electron in the innermost orbit having the smallest energy and the electron in the outermost orbit having the largest energy. 
  • When an atom is provided energy either by strong heating or by bombardment with some fast-moving particle, Electrons in a natural state can jump to higher energy levels. But the atom doesn’t remain in that state for more than 10^-8 s & comes back to a normal lower energy level, emitting surplus energy in the form of Photons.
  • Emitted energy can be Visible, UV or X-Ray, depending on the energy difference. 
Basics of Radioactivity


  • The property under which a heavy nucleus of an element disintegrates itself into smaller nuclei along with alpha, beta & gamma rays without being forced by any external agent to do so is termed radioactivity. 
  • The phenomenon of radioactivity is natural and can’t be stopped. 
  • It is found that all atoms with more than 83 protons; and a neutron-to-proton ratio of more than 1 as they are unstable. To achieve stability, unstable nuclei disintegrate spontaneously with the Alpha, Beta & Gamma Rays emission. 
  • Henry Becquerel discovered the phenomenon of radioactivity.

Reason of Radioactivity

  • Inside the nucleus, positively charged Protons & Neutral are present. Hence, if only Electrostatic Force is there, all nuclei must have split apart due to repulsive forces. But this is not the case & the nucleus is stable.
  • But another force called Nuclear Force is working here. IT IS ATTRACTIVE FORCE EXISTING BETWEEN PROTON & PROTON and PROTON & NEUTRON. BUT THIS FORCE ACTS AT A VERY SMALL DISTANCE. Generally, Nuclear Forces overpower Electrostatic Forces inside the nucleus.
  • But in the case of larger nuclei, nuclear forces cannot overpower electrostatic forces, and they exhibit radioactivity.

Alpha, Beta & Gamma Radiations

 The most common types are

  Alpha  Beta Gamma
  Similar to Helium Nuclei (He (2,4)) and generally emitted by a large nucleus These are fast energy electrons   Gamma Radiations are electromagnetic radiations of high frequency
Generally emitted by unstable atoms to become stable by releasing energy
Penetration  It can penetrate  5 cm of air only. It can penetrate air and paper. It can penetrate most things except a thick sheet of lead or a very thick concrete wall.  
Mass Heaviest (4 amu) Lighter (9.1 X 10^-31 kg) Massless    
Speed Around 1/100 of the speed of light 33% to 99% of the speed of light Equal to the speed of light
Ionising power Maximum due to maximum charge (+2) and maximum mass Intermediate between beta & gamma Minimum due to zero charge
Effect on Photographic plate Produce smaller effect More effect Maximum effect
Effect of Electric and magnetic field Show deflection Show deflection Don’t show any deflection
Effect on the human body It causes a burning effect It can cause a shock on longer exposure It can cause cancer


  • Transmutation is the process of altering one element to another. 
  • Reason = Natural Radioactivity, Artificial Transmutation etc.
  • Artificial Transmutation is used to obtain elements with Atomic numbers greater than 92.

Half Age

It measures the time it takes for a given amount of the radioactive substance to become reduced to half due to decay and, therefore, the emission of radiation.

Half Age of Radioactivity

Carbon Dating

  • The technique of estimating the age of the remains of a once-living organism, such as a plant or animal
  • It involves measuring the radioactivity of its C-14 Content (the half-life of C-14 is 5570 years).
  • The ratio of C-14 / C-12 in nature is 1/106. 

Uranium Dating

  • Uranium Dating is used for dating older but non-living things like rocks. 
  • The age of rocks from the moon has been estimated to be 4.6 X 10^9 years, nearly the time of Earth’s origin.

Isotope, Isobars & Isoneutrons

  • Atomic Number (Z) = Number of Protons
  • Mass Number (A) = Number of Neutrons & Protons


  • Isotopes are nuclides with same Atomic Numbers but different Mass Numbers.
  • E.g., U (92,235) & U (92,238 ) + C-12 & C-14
  • Generally, isotopes don’t have different names except for isotopes of Hydrogen named Protium (H(1,1), Deuterium (H (1,2)) & Tritium (H(1,3)).


  • Isobars are nuclides having same Mass Number but different Atomic Numbers.
  • E.g., K (19,40) & Ca (20,40) + C (6,14) & N (7,14) 
  • They have different names. 


  • Isoneutrons are nuclides having the same number of neutrons.
  • Examples include 
    1. C (6,14) & O(8,16): Both have 8 neutrons
    2. H (1,3) & He (2,4): Both have 2 neutrons