Fine structure of the deep-band probeKβ2,5in copper

The x-ray line $K{\beta }_{2,5}$, formally corresponding to the transitions $4p\to 1s \mathrm{and} 4s$, $3d\to 1s$, respectively, was studied using electron excitation of polycrystalline copper. The kinetic energy of the electrons ranged from 20 to 40 keV. The spectrum was decomposed by means of successive reflections in two highly perfect Si crystals which were bent elastically in such a manner that optimal intensity and resolving power were achieved. A numerical calculation of the latter quantity yielded an experimental window which was extremely narrow, compared with the theoretical lifetime width of the $1s$ core state (0.03 vs 1.5 eV). The energy position of the Fermi edge was located by means of the observed absorption curve. The profile and apparent strength of the high-energy satellite $K{\beta }^{\prime \prime \prime }$ were found to depend on the high voltage and the take-off angle. The influence of self-absorption is discussed and it is concluded that the main features of the structure earlier known as $K{\beta }^{\prime \prime \prime }$ may be explained as selective absorption of a featureless Fermi-edge tail, which has a substantial intensity and which originates in incomplete relaxation or multiple ionization. The emission band below the edge is shown to exhibit a new feature just at the low-energy side of the main peak, causing a slight local asymmetry. There seems, however, to be no incompatibility between this structure, or the rest of the intensity variations, and density-of-states calculations.