Channels of Inner-Shell Vacancies

Radiative decay An inner-shell vacancy is filled by an electron from an intermediate or outer shell this process transfers the vacancy from an inner shell to a higher shell. The energy difference between the initial and the final state is carried away by a photon resulting in the emission of the 

Auger decay The interaction of two electrons in higher shells by the electrostatic repulsion forces one of the two electrons to fill the inner-shell vacancy while the other electron is emitted into the continuum, thereby carrying the excess energy as kinetic energy. 

Coster-Kronig decay Tliis decay process is a special Auger decay in which the original vacancy is transferred to a higher subshell of the same shell. Auger and Coster-Kronig transitions are (essentially) two-electron processes and cause the emission of electrons with characteristic energies. 

An accurate knowledge of the individual rates of vacancy decay is interesting in several fields. Firstly, transition rates present a sensitive tool to investigate details of atomic structure since they probe static properties (atomic wave functions) as well as dynamic properties (electron correlation and relaxation). Secondly, an accurate knowledge of relative decay rates is important in practical applications In experimental studies of ion-atom collisions either fluorescence or electron emission is detected and the ionization cross sections are derived. In the L-shell case uncertainties of fluorescence and Coster-Kronig yields are a limiting factor upon deriving ionization cross sections.  

Comprehensive theoretical calculations of radiative transition rates as well as Auger and Coster-Kronig transition rates are available. However, uncertainties are large for Coster-Kronig transitions with small excess energy due to the strong influence of several effects (i) many-body interactions in the initial and final atomic systems, (ii) relaxation in the final ionic state, and (iii) exchange interaction between the continuum electron and the final bound-state electrons. For an experimental determination of decay rates, various techniques have been employed, e.g., the use of radioactive sources or coincidence techniques. Most techniques 

---