# Kerma

Quantity for ionising uncharged particles, defined by the quotient of [math]dE_{tr}[/math] by [math]dm[/math], where [math]dE_{tr}[/math] is the mean sum of the initial kinetic energies of all the charged particles liberated in a mass [math]dm[/math] of a material by the uncharged particles incident on [math]dm[/math], thus:

[math] K = \frac{dE_{tr}}{dm} [/math]

The SI unit of kerma is joule per kilogram (J kg^{-1}), and its special name is gray (Gy).

‘Kerma’ is an acronym for ‘kinetic energy released in a mass’.

(Adapted from ICRP Publication 116, 2010)

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## Previous glossary entries

### from ICRP Publication 103, 2007; ICRP Publication 119, 2012; ICRP Publication 120, 2012; ICRP Publication 135, 2017; and ICRP Publication 136, 2011

The quotient of the sum of the kinetic energies, [math]dE_{tr}[/math], of all charged particles liberated by uncharged particles in a mass [math]dm[/math] of material, and the mass [math]dm[/math] of that material.

[math] K = \frac{dE_{tr}}{dm} [/math]

Kerma is defined as a non-stochastic quantity and [math]dE_{tr}[/math] is the expectation value of the sum of the kinetic energies. The unit for kerma is joule per kilogram (J kg^{-1}) and its special name is gray (Gy).