Among Alpha, Beta and Gamma radiations:
1. The Alpha Particles have highest ionising power but least penetrating power
2. The Gamma radiations have highest penetration power but lowest ionising power
Which among the above is / are correct statements?

Answer: [C] Both 1 & 2


  1. They are doubly ionised helium nuclei having a mass equal to 6.64 × 10–27 kg and charge equal to 3.2 × l0–19 C.
  2. They have the highest ionising power.
  3. They have the least penetrating power.
  4. They produce fluorescence in the zinc sulphide screen.



  1. They are negatively charged particles, having a charge equal to –1.6 × 10– 19 C and mass 9.1 × 10–31 kg.
  2. They have more penetration power than α-particles.
  3. They have less ionising power than α-particles.
  4. They affect photographic plate.



  1. They are electromagnetic waves, having wavelength less than 0.01 Å.
  2. They have a very high penetration power.
  3. They have a very low ionising power.
  4. They are not affected by electric or magnetic fields.

Notes on Ionising power

If one unit is ionising power of γ-radiations, then 100 units is ionising power of β-particles and 10000 units is the ionising power of α-particles.

Notes on Penetration power

γ-radiations can penetrate even 30 cm of iron. β-particles can penetrate 1mm of lead or 5 mm of aluminium. α-particles can penetrate 2.7 to 8.6 cm of air

This question is a part of GKToday's Integrated IAS General Studies Module