3.8.1.2
Comparing alpha, beta and gamma: a summary table
Nuclear Structure & Radiation — AQA A-Level Physics
- Alpha: range 3-7 cm in air, highly ionising, weakly penetrating, stopped by paper.
- Beta: range 20 cm - 3 m in air, moderately ionising, moderately penetrating, stopped by ~3 mm aluminium.
- Gamma: infinite range (inverse square law), weakly ionising, highly penetrating, reduced by thick lead or concrete.
- In electric fields: alpha deflects towards the negative plate, beta-minus towards the positive plate, gamma passes straight through.
- In magnetic fields: alpha and beta follow curved paths (opposite directions). Beta curves more due to lower mass. Gamma is unaffected.
Common Mistake
MEDIUM
Students often: Avoid saying gamma radiation is 'stopped' by lead.
Instead: Gamma intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. is reduced by lead, but never fully stopped. The correct phrase is 'the intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. is significantly reduced'. Only alpha and beta are absorbed completely.
Instead: Gamma intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. is reduced by lead, but never fully stopped. The correct phrase is 'the intensityThe powerThe rate of energy transfer. Measured in watts (W). transmitted per unit area perpendicular to the wave direction. Measured in W m⁻². Proportional to amplitude squared. is significantly reduced'. Only alpha and beta are absorbed completely.