Atoms, Nuclei and Radiation
What is Radiation?
Think of a nucleus as a bustling city. When it gets too crowded or unstable, it releases energy in the form of particles or waves. These releases are called radiation and come in three main flavours: alpha (α), beta (β) and gamma (γ).
1. Composition
- α‑radiation: a helium nucleus – 2 protons + 2 neutrons.
- β⁻‑radiation: an electron (e⁻) emitted from a neutron‑rich nucleus.
- β⁺‑radiation: a positron (e⁺) emitted from a proton‑rich nucleus.
- γ‑radiation: a high‑energy photon (γ‑ray), no mass, just energy.
2. Mass
Mass is measured in atomic mass units (u). The heavier the particle, the more it slows down when it passes through matter.
| Radiation | Mass (u) |
|---|
| α | 4.002602 |
| β⁻ / β⁺ | 0.00054858 |
| γ | 0 (photon) |
3. Charge
Charge determines how the particle interacts with electric and magnetic fields.
- α‑particle: +2 e (two positive charges).
- β⁻‑particle: –1 e (one negative charge).
- β⁺‑particle: +1 e (one positive charge).
- γ‑ray: neutral (no charge).
4. Penetrating Power & Range
Think of each radiation type as a different type of “bullet”:
- α‑particles: heavy & charged – stop in a few centimetres of air or a sheet of paper.
- β‑particles: lighter & charged – travel a few metres in air, can be stopped by a few millimetres of aluminium.
- γ‑rays: massless & neutral – can pass through many centimetres of lead; only heavy shielding works.
5. Real‑World Analogy
Imagine a crowded stadium (the nucleus). If a group of four people (α) leaves, they’re heavy and slow, so they can’t go far. If a single person (β) leaves, they’re lighter and can move faster. If a flash of light (γ) is emitted, it’s like a laser beam that can go straight through walls unless you block it with a heavy shield.
6. Exam Tips
Remember:
- Use the mass–charge–penetration triangle to quickly identify radiation type.
- Write the half‑life formula: \$t_{1/2} = \frac{\ln 2}{\lambda}\$ when asked about decay.
- For β⁺ decay, remember the positron annihilates with an electron, producing two 511 keV γ‑photons.
- When comparing shielding, order from most to least effective: lead > steel > aluminium > paper.
Good luck, and keep exploring the tiny world inside atoms! 🚀