4 upwards, energy loss of particles traversing a medium starts to increase logarithmically because of relativistic effects (up to 
, the loss of energy decreases with 
as expected even from a classical point of view where energy loss is related to the number of collisions of the traversing particle with the atoms of the medium). At high values of 
100),
the rate of ionization energy loss saturates due to density effects (
Fermi plateau ). In noble gases with high Z, the Fermi plateau is about 1.5 to 1.7 times the minimum ionization.
With knowledge of the particle momentum, the relativistic rise can be used for hadron identification over a wide range of momenta;
taking 
and K mesons and protons as an example: 
separation using the relativistic rise is possible from 2 to 50
GeV/c, K/p from 5 to 40 GeV/c. In argon (at 
temperature and 760 mm pressure Hg) the relative ionization for particles of 10 GeV/c is
For details, see [Allison91]. For an example of measuring the relativistic rise, see [Breuker87].