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Using monochromatized synchrotron radiation a sample of thin samarium and titanium foils was excited, and the induced Sm L X-rays and Ti K X-rays were detected by a Si(Li) detector. When the primary photon energy is tuned across the Sm L2 and L1 edges, the intensities of the Sm L X-ray lines normalized to the Ti K alpha intensity exhibit abrupt changes. From these intensity changes the Coster-Kronig factors were determined: f23=0.14+or-0.03, f13=0.18+or-0.03 and f12=0.19+or-0.03. The value of f13 is substantially smaller than predicted by theory and extrapolated from heavier elements. Furthermore, from the total intensities of all lines originating from the same Sm L subshell the ratios of the fluorescence yields omega 1/ omega 3=0.48+or-0.07 and omega 2/3=1.05+or-0.05 were obtained.

The individual decay channels of samarium L-subshell vacancy states @&ere experimentally investigated by the synchrotron photoionization method. For the Coster-Kronig yield f~" i.e. , the relative contribution of the nonradiative Ll-L3 channel to the total decay of Ll-vacancy states, the value f» =0.1920.03 was obtained. This is a surprisingly small value regarding both prediction from theory (e.g. , f» =0.32 according to Chen, Craseman, and Mark [Phys. Rev. A 24, 177 {1981)])and extrapolation from neighboring elements (f "=0. 32 for the elements with Z =72-74 according to our previous work [U. Werner and W. Jitschin, Phys. Rev. A 38, 4009 (1988)]). PACS number{s): 32.80.Hd, 32.80.Fb, 31. 20.TzInner shells of atoms bear the fascination of conceptual simplicity due to the hydrogenic nature of inner-shell vacancies. Energy levels of K and L shells are predicted by ab initio relativistic calculations with uncertainties below 0.1% [1 -3] and radiative transition rates with uncertainties below 10%. However, the nonradiative decay deserves special attention: although this two-electron process was discovered already in 1922 [4] and has been the subject of considerable theoretical effort [5 -7], severe deviations between calculated transition rates and experimental results have been observed in a number of cases [8,9]. The situation becomes particularly bad when the excess energy of the nonradiative decay is small. In such a case the slowly outgoing electron interacts with the residual atomic electrons. As a consequence, the twoelectron model fails and the decay of a vacancy state becomes a multielectron process [10]. The L, subshell provides a particular interesting testing case for the nonradiative transitions since the radiative decay plays only a minor role (the radiative yield remains below 20% for all stable elements [11]) and since the various nonradiative decay channels (Auger, L, L3 Coster-Kro-nig, L, -L 2 Coster-Kronig) with substantially different excess energies compete with each other. For elements with Z~80 or Z~47 the L,-L3M~5 Coster-Kronig transition is the dominant decay channel; however, for elements with intermediate Z this channel is blocked for energy reasons [12]. Accordingly, the L, L3 Coster-Kronig -yield f&3 changes strongly in the regime of these Z numbers (Fig. 1).Experimental data on the various nonradiative yields (Auger, Coster-Kronig) are scarce and for lighter elements practically nonexisting [8,11,13,14]. The recently introduced method of photoionization of consecutive subshells by tunable synchrotron radiation is capable of providing reliable results for all L-subshell yields [15].By this method comprehensive f,3 data for elements Z =72-82 and also data for lighter elements have been obtained [16,17]. The experimental values for f&3 are in reasonable agreement with theoretical calculations. This result is remarkable in particular for Z =80 where the excess energy of the dominating L,-L3M Auger transition is rather small (about 100 eV [12] compared to the L, binding energy (about 15 ke...