Lineal energy

The quotient of $ε_i$ by $\bar{l}$ , where $ε_i$ is the energy imparted to the matter in a given volume by a single energy-deposition event $i$ , and $\bar{l}$ is the mean chord length of that volume, thus:

$y=\frac{ε_i}{\bar{l}}$

The SI unit of lineal energy is joule per metre (J m^-1), often given in KeV μm,^-1 (ICRP Publication 123, 2013)