The x ray spectra and the response of conduction electrons to a potential change: The phase-shift operator approach

If a scattering potential in a simple metal is changed the transient response of the conduction electrons as they adjust to the new ground state is nontrivial. It is this response which leads to the singular edge in the soft x ray spectra of a simple metal. A new method of treating such problems is presented. When this method is applied to the x ray problem the shape of the singular edge may be derived in an elementary manner.