  The optical model is a fundamental tool to describe scattering processes in
nuclear physics. The basic input is an optical model potential, which describes
the refraction and absorption processes more or less schematically. Of special
interest is the form of the absorption potential. With increasing energy of the
incident projectile, a derivation of this potential must take into account the
observed energy dependent transition from surface to volume type. The classic
approach has weaknesses in this regard. We will discuss these deficiencies and
will propose an alternative method based on concepts developed within the
framework of fractional calculus, which allows to describe a smooth transition
from surface to volume absorption in an appropriate way.
