Nuclear radiation: alpha, beta, gamma and nuclear equations
Types of nuclear radiation
Unstable nuclei emit radiation to become more stable. There are four types of nuclear radiation you need to know:
| Type | Symbol | Nature | Charge | Mass | Penetration | Ionising power |
|---|---|---|---|---|---|---|
| Alpha | α | 2 protons + 2 neutrons (helium nucleus) | +2 | 4 | Stopped by paper / few cm air | High |
| Beta | β | Fast electron from nucleus | −1 | ~0 | Stopped by 3 mm aluminium | Medium |
| Gamma | γ | High-frequency EM wave | 0 | 0 | Reduced by thick lead / metres concrete | Low |
| Neutron | n | Neutron | 0 | 1 | Reduced by concrete / water | Low–medium |
Deflection in electric and magnetic fields
- Alpha (+2 charge): deflected towards negative plate; deflected in a magnetic field (relatively small deflection — large mass).
- Beta (−1 charge): deflected towards positive plate; deflected in opposite direction to alpha in magnetic field (larger deflection — much smaller mass).
- Gamma (0 charge): NOT deflected by electric or magnetic fields (no charge).
Nuclear equations
Nuclear equations show the change in atomic number (Z) and mass number A during decay.
Notation: ᴬ_Z X, where A = mass number (top), Z = atomic number (bottom).
Conservation rules:
- Mass numbers (top) must balance on both sides.
- Atomic numbers (bottom) must balance on both sides.
Alpha decay
Loses a helium nucleus (⁴₂He):
- Mass number decreases by 4
- Atomic number decreases by 2
Example: ²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
Beta decay
A neutron converts to a proton and emits an electron (⁰₋₁e):
- Mass number unchanged
- Atomic number increases by 1
Example: ¹⁴₆C → ¹⁴₇N + ⁰₋₁e
Gamma emission
No change in mass number or atomic number — the nucleus just loses energy. Often accompanies alpha or beta decay.
Contamination vs irradiation
| Contamination | Irradiation | |
|---|---|---|
| Definition | Radioactive material deposited ON or IN the body | Exposure to radiation from an external source |
| Risk | Ongoing — source stays with you | Stops when you move away |
| Most dangerous type | Alpha (inside body, short range → concentrated ionisation) | Gamma (penetrates body from outside) |
Applications and risks
| Use | Radiation type | Reason |
|---|---|---|
| Medical imaging (PET scans) | Gamma (positron → γ) | Penetrates body; detected outside |
| Cancer treatment | Gamma | Kills cancer cells |
| Smoke detectors | Alpha | Ionises air; stopped by smoke particles |
| Tracers in industry | Beta or gamma | Can be detected through pipes/containers |
| Sterilisation of equipment | Gamma | Kills bacteria; penetrating |
⚠Common mistakes
- Beta emission: a beta particle is an electron — from the NUCLEUS (a neutron splits into a proton + electron). It is NOT an orbital electron.
- Gamma has no charge and no mass — nuclear equations with gamma: A and Z do not change.
- Alpha is most ionising but least penetrating (stopped by skin or paper). Outside the body it's less dangerous; inside (inhaled/ingested) it's very dangerous.
- Balancing nuclear equations: check both top (mass) AND bottom (atomic number) sum to the same values on each side.
AI-generated · claude-opus-4-7 · v3-edexcel-combined-science