Types of Radioactivity

Radioactivity happens when an unstable nucleus gives out energy or particles to become more stable. These emissions are spontaneous (they happen on their own) and random (you cannot predict exactly when or in which direction).

The Three Types

Alpha (α)

Nature: a helium nucleus (2 protons + 2 neutrons), charge +2, relatively heavy.
Ionising: high (knocks many electrons off atoms).
Penetration: low (stopped by paper or skin; a few cm in air).
Deflection: small bend in electric/magnetic fields, towards the negative plate.

Beta (β−)

Nature: a fast electron from the nucleus when a neutron changes into a proton, charge −1.
Ionising: medium.
Penetration: medium (stopped by thin aluminium).
Deflection: strong bend, opposite direction to α, towards the positive plate.

Gamma (γ)

Nature: electromagnetic wave (photon), no mass, no charge.
Ionising: low (indirect ionisation).
Penetration: high (needs thick lead or concrete).
Deflection: none in electric or magnetic fields.

How the Nucleus Changes

• Alpha decay: mass number decreases by 4; atomic number decreases by 2 (new element).
• Beta (β−) decay: a neutron turns into a proton + electron; atomic number increases by 1; mass number unchanged: $\text{neutron} \to \text{proton} + e^-$.
• Gamma emission: no change in mass or atomic numbers; only energy is lost.

Decay Equations (Nuclide Notation)

Alpha example:

$$\,^{238}_{92}\text{U} \;\to\; ^{234}_{90}\text{Th} \;+\; ^{4}_{2}\text{He}\,$$

Beta (β−) example:

$$\,^{14}_{6}\text{C} \;\to\; ^{14}_{7}\text{N} \;+\; ^{0}_{-1}\beta\,$$

Key Ideas and Misconceptions

• Emissions are random and spontaneous; you cannot speed them up by heat or pressure.
• Beta particles come from the nucleus (not the electron cloud).
• Gamma is radiation (a wave), not a particle with charge or mass.