Unexpectedly small intrashellL1-L3vacancy transition rate in

Abstract

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...

Study of vacancy decays in the L-shell photoionization of barium in the excitation energy range of 5.6–30 keV: from L2edge to energy high above the thresholds of double L-vacancy production

“…With the advent of modern synchrotron radiation (SR) sources, photoionization methods offer substantial advantages in studying the intrashell vacancy transfer processes due to the precise energy tunability of the exciting photon beam, which enables us to selectively ionize a particular subshell of the target element. With the aid of this method, Jitshin and his coworkers [41][42][43][44][45] have studied the intrashell vacancy transfer processes and performed accurate measurements for the CK yields. It is well known that different L subshell photoionization cross sections show different excitationenergy dependences.…”

Quality Assurance Challenges in X-ray Emission Based Analyses, the Advantage of Digital Signal Processing

“…This widely used parameter was calculated in the relativistic Hartree-Slater (RHS) model. Extensive measurements made by Jitschin and coworkers [9][10][11] found significant deviations from the RHS predictions. This was not entirely unexpected as the theoretical model, that includes the perturbation from the external field, could successfully account for the experimental data.…”