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IAEA
The mean
excitation potential I
is a geometric mean value
of all ionization and excitation potentials of an atom of the
absorbing material.
I
values are usually derived from measurements of
stopping powers in heavy charged particle beams, for
which the effects of scattering in these measurements is
minimal.
•
For elemental materials
I
varies approximately linearly with
Z
,
with, on average,
I
= 11.5 x
Z
.
•
For compounds,
I
is calculated assuming additivity of the collision
stopping power, taking into account the fraction by weight of each
atom constituent in the compound.
2.5 INTERACTION COEFFICIENTS: ELECTRONS
2.5.4 Mass stopping power for electrons and positrons