PHYSICAL REVIEW A VOLUME 47, NUMBER 2 FEBRUARY 1993 L x-ray Auorescence cross sections and intensity ratios in some high-Z elements excited by 23. 62- and 24.68-kev photons D. V. Rao Dipartimento di Fisica, Uniuersita di Roma "La Sapienza, "piazza Aldo Moro 2, 00185 Roma, Italy R. Cesareo Centro Interdipartimentale di Ricerca per L'Analisi dei Modelli e dell'Informazione nei Sistemi Biomedici, Uniuersita di Roma "La Sapienza, "piazza A ldo Moro 2, 00185 Roma, Italy G. E. Gigante Dipartimento di Fisica, Uniuersita di Roma "La Sapienza, "piazza Aldo Moro 2, 00185 Roma, Italy and Centro Interdipartimentale di Ricerca per L Analisi deli Modelli e dell Informazione nei Sistemi Biomedici, Uniuersita di Roma "La Sapienza, "piazza Aldo Moro 2, 00185 Roma, Italy (Received 3 August 1992) Ll, La, LP, and L y x-ray Auorescence cross sections have been measured for the elements Pr, Ho, Yb, Au, and Pb using photon energies of 23.62 and 24.68 keV. Measurements have been performed using an x-ray tube with a secondary-exciter system as the excitation source. The secondary exciters of Cd and In were pure metals () 99.9%). The x-ray tube with a secondary-target arrangement was used to obtain high intensity with a high degree of monochromatization. By using an x-ray tube, it is possible to mea- sure x-ray Auorescence cross sections and ratios even for low-intensity x rays (Ll). Experimental results have been compared with the theoretically calculated values of L x-ray Auoresence cross sections. A fairly good correspondence is observed between experimental and calculated values. The intensity ratios for the intense transitions IL&/II are in good agreement with the calculated values. PACS number(s): 32. 80. Hd, 32.30. Rj INTRODUCTION Studies of the L x-ray fluorescence cross sections of many elements and their intensity ratios have been re- ported in the past [1 — 6]. Accurate determination of L x- ray fluorescence cross sections and their intensity ratios for different elements is important because of their wide use in the fields of atomic, molecular, and radiation phys- ics, and in nondestructive elemental analysis of materials using either traditional photon sources or synchrotron ra- diation [7]. L x-ray fluorescence cross sections and their intensities can be calculated by using photoelectric cross sections, fluorescence yields, and fractional emission rates. Uncer- tainties in these tabulated quantities largely reflect the er- ror in L x-ray fluorescence cross sections. For this reason most users prefer the experimental values of the cross sections whenever large discrepancies are observed be- tween theoretical and experimental values. For quantita- tive analytical applications it is necessary to know the different relative intensities of the photons that contrib- ute to the fluorescence. Since fluorescence cross sections increase as the energy decreases, the contributions to L x-ray fluorescence of low-energy, low-intensity transitions can be very important. Earlier experimental L x-ray fluorescence cross sec- tions and their intensity ratios were measured using ra- dioisotopes as excitation sources. They have the advan- tages of stable intensity and energy and of small size, which allows compact and efficient geometry, and they operate without any external power. The drawbacks are the small number of suitable radioisotopes available at different excitation energies and the decline of intensity with time if the half-life is of the order of a few years or shorter, and the relatively low flux. An alternative to radioisotopes is use of an x-ray tube with a secondary-target arrangement. In secondary- target arrangements, the primary radiation generated by the electrons is used to excite the secondary target. In this process, the major part of the bremsstrahlung radia- tion generated by the first target is eliminated and the ra- diation from the secondary target has a high degree of monochromatization with high intensity. The present measurements have been performed with an x-ray tube with a secondary-exciter system as the excitation source instead of radioisotopes. By using an x-ray tube it is pos- sible to measure I x-ray fluorescence cross sections even for low intensity x rays (L 1). In addition, these measurements serve to provide a check on the theoretical calculations of some of the fun- damental physical parameters, such as L-subshell ioniza- tion cross sections, fluorescence yields [8], Coster-Kronig transition probabilities [9], and radiative decay rates [10], the direct determination of which presents many difficulties. The K x rays of Cd and In provided incident photons with energies of 23.62 and 24. 68 keV, respectively. The choice of the incident energies was such that the K-shell electrons from the target element were not knocked out. The vacancies were therefore not transferred from the K to the L shell. 47 1087 1993 The American Physical Society