# Kerma

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

$K = \frac{dE_{tr}}{dm}$

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)

The quotient of the sum of the kinetic energies, $dE_{tr}$, of all charged particles liberated by uncharged particles in a mass $dm$ of material, and the mass $dm$ of that material.
$K = \frac{dE_{tr}}{dm}$
Kerma is defined as a non-stochastic quantity and $dE_{tr}$ 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).