Gamma radiation is an electromagnetic wave: weakly ionising, highly penetrating

Nuclear Structure & Radiation — AQA A-Level Physics

Key Definition

Gamma radiation — High-energy electromagnetic radiation emitted from the nucleus. No mass, no charge. Notation: ⁰₀γ.

Emitted when a nucleus needs to lose energyThe capacity to do work. Measured in joules (J)., often after alpha or beta decay.
Least ionising — ~1 ion pair per cm in air.
Most penetrating — infinite range, follows an inverse square law. Reduced by thick lead or several metres of concrete.
Not deflected in electric or magnetic fields (no chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C).).
Widely used in cancer radiotherapy and sterilising medical equipment.

I = \frac{k}{x^2}

$I$: 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. of gamma radiation (W m⁻²)
$k$: constant of proportionality
$x$: distance from the source (m)

Examiner Tips and Tricks

The inverse square law applies ONLY to gamma radiation, not alpha or beta.
Alpha and beta are absorbed too quickly to spread out as a sphere.
When asked about the inverse square law in an exam, always specify it is for gamma.