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α, β & γ rays are called nuclear radiations

Interaction of nuclear radiations with matter depends on three characteristics of nuclear radiations.

1. Mass of particles
2. Charge
3. Energy

Interaction of α-Rays

• α-particle can do ionization in the following two ways

1. Mechanical collision ( α-particle directly hits electron)
2. Coulomb’s interaction ( electrostatic interaction )]

• Mode of ionization by Coulomb’s interaction for α-rays dominates over that by direct collision.
• The path of ionization followed by α-rays is straight and continuous because of its high ionization power and large mass.
• During ionization, α-particle continuously looses its energy as a result of which its velocity decreases.
• In each collision, α-particle loses an average of 35eV energy.
• 7.7 MeV α-particle produces 2 x 10⁵ ion pairs before stopping.
• When α-particle has spent all its energy on ionization, it absorbs two electrons from its surroundings gas and becomes a neutral (He atom)
• Range of α-particle in air is small due to intense ionization.
• 7.7 Mev α-particle has 7cm range in air at S.T.P, which reduces further in denser medium.
• Range of 7.7 MeV α-particle in aluminum is only 0.04 mm
• α-particle produces disintegration in nuclei of some atoms if they have high energy.

Interaction of β-Rays

• β-particles are fast electrons or positrons coming from nucleus.
• Range of β-particle is larger than that of α-particle by a factor of 100.
• Ionization of β-particle is smaller than that of α.
• Mass of β-particle is equal to that of an electron.
• Charge of β-particle is equal to 1.6 x 10¹⁹ C that may be positive for positron [β⁺] and negative for electron [β^-].
• β-particle does ionization due to electrostatic repulsion ( in case of β^-) and attraction ( in case of β⁺).
• Ionization path of β is broken and zigzag due to its smaller mass.
• Ionization by head-on-collision is very rare.
• Β-particle looses almost all its energy in a single encounter.
• Because of lesser ionization encounters, penetration of β is 100 times larger than that of α-particle of same energy.
• 3 MeV β-particles can pass through 6.5 mm aluminum foil.
• β-particle can produce fluorescence.

Interaction of γ-Rays

• γ-rays being photons can’t be stopped by matter ( lead can be used as a shield because of its high electron density)
• γ-rays have shorter wavelength than X-rays.
• γ-rays loose their energy by following three ways

1. Photoelectric effect
2. Compton effect
3. pair production

• The type of interaction depends upon energy range of photon available according to following scheme:

Interaction of Neutrons

• Neutrons are more effective radiation than both α and β rays because they bear no charge as regard to penetration.
• When neutron is captured by a nucleus, it results in the formation of a radioisotope.
• Neutron causes fission in heavy nuclei.
• Neutron can knock down electrons out of body cells causing instantaneous death.