the knocked-out electron leaves the atom as a "free" electron and the atom becomes ionized. because ionization is an excited state, the atom will quickly return to its normal state after refilling the inner electron vacancy by an outer shell electron. in the meantime, the energy difference between an outer shell electron and an inner shell electron rill generate either an x-ray photon(characteristic x-ray) or another characteristic free electron that is emitted from the atom. the latter is called as the auger electron, which also can be used for elemental analysis; this is discussed in chapter7