3.8.1.2
Alpha particles are helium nuclei: highly ionising, weakly penetrating
Nuclear Structure & Radiation — AQA A-Level Physics
Key Definition
Alpha particle — A helium nucleus containing 2 protons and 2 neutrons. Mass = 4 u, charge = +2e. Notation: ⁴₂α.
- Emitted by nuclei that are too large (too many nucleons).
- Most ionising radiation type — produces ~10,000 ion pairs per cm in air.
- Least penetrating — range of 3-7 cm in air. Stopped by a single sheet of paper.
- Deflected slightly in strong electric and magnetic fields. Deflects towards the negative plate in an electric field.
- High chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). (+2e) makes it strongly ionising, but high mass (4 u) means it loses energyThe capacity to do work. Measured in joules (J). quickly.