The active region of x-ray emission was studied. The x-ray emission rates for K and L x-rays were calculated as a function of the maximum radial distance in integration of matrix elements for radiative transitions and the radius of the active region of x-ray emission was determined. This radius depends on the multipolarity of the transition and also the sum of numbers of nodes of the wavefunctions concerned. The approximate expression for the radius of the active region is obtained in terms of the mean radius of the wavefunction for the initial vacancy state. Applications of the present results to multiple ionization and to chemical effects are discussed.
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