The Auger emission has been detected by Pierre Auger more than eighty years ago;
short after the beginning of quantum mechanics. The observation of radiation free
transitions perfectly complemented the case of electron emission due to photon impact.
The emission of an electron after photoionization had been already understood
and explained by the work of Einstein (1905, Nobelprize 1921 for the photoelectric
effect). Wentzel (1927) was first by theoretically interpreting the Auger emission as
a process caused by a two-particle interaction. Since photoionization had been already
explained as a single-particle interaction effect, and due to the fact that first
experiments mainly concentrated on the detection of the valence shell electrons, the
investigation of radiation free transitions, i.e. the Auger effect, showed only little
development during the early decades of the last century. Only starting in the early
1980s, scientific interest came back. This has been caused due to the availability of
improved and more developed detection methods and, on the theoretical side, by the
application of advanced methods of density matrix theory which allowed for more
precise predictions, like angular distribution and spin polarization, of the observed
particles, i.e. the Auger electrons. It is worth pointing out that both, theoretical as
well as experimental progress, benefited from efforts which had been made in the
field of nuclear physics. In particular the work by Fano (1957) and co-workers need
to be mentioned who first adapted the nuclear physics methods and successfully
applied them to electron emission problems in atomic physics. Adopting the experimental
techniques of nuclear physics, like angle and spin resolved observation of
particles, there has always been, and still is, need for a theoretical interpretation and
prediction of angle and spin resolved data. This need is even more urgent due to
the fact that, after starting investigations of angle and spin resolved Auger emission
in the early 1980s, the scientific community is today, due to the availability of
third generation synchrotron radiation sources and more refined detection methods,
able to produce and obtain reliable data which can be compared with the theoretical
predictions. This book is intended to focus on these still important areas of Auger
emission theory. Our aim is to derive the theoretical framework and to provide a
number of data and useful relations necessary for the interpretation of present and
forthcoming experiments.