10 th International Conference on Particle Induced X-ray Emission and its Analytical Applications PIXE 2004, Portorož, Slovenia, June 4-8, 2004 http://pixe2004.ijs.si/ 810.1 Comparative Study of W-K and L Shells Relative Yield Ion Energy Dependence P. C. Chaves; M.A. Reis ITN, EN10 Sacavém, Apartado 21, 2686-953 SACAVÉM, PORTUGAL ABSTRACT In a previous work, it was shown that the yield of L shell x-rays relative to the L α transition was depending on the irradiation ion beam energy. Diagrams of change trends, were established and shown to vary for different chemical species of W. In this work, the extension of the method to the K shell x-rays of W is explored. K x-ray spectra were measured using a CdTe detector since Si(Li) detectors are useless at the 58-67 keV energy range covered by W K x-rays. To be able to compare results the L shell x-rays studied were limited to the L 1 shell and the yields were normalized to the L β3 line. It is shown that, although the ionisation step is excluded in this way, changing trends are still observed. Keywords: PIXE, chemical speciation, ion energy scan, relative yield ion energy dependence, K x-ray spectra. 1. INTRODUCTION Although PIXE analysis using K α or L α transitions is presently a common task, the use of other lines of the x-rays spectra still remains significantly unexplored. In this work, it is discussed that differences in yields ratios not only are dependent on the chemical state of the element, as pointed out by many authors [1,2], but do also show dependencies on the incident ion beam energy, as shown elsewhere for the whole L spectra of W [3]. In the present work, these dependencies are seen in ratios within both 1S and 2S shells, excluding both ionization step and therefore fluorescence coefficients effects. The observed effects must reside on the decay stage of the process, although its origin is not yet understood. 2. EXPERIMENTAL In the present study three W compounds (pure W, Lithium Tungstaste (Li 2 WO 4 ) and phosphotungstic acid (P 2 O 5 ·24WO 3 ·xH 2 O)) were irradiated using various conditions of H + ion beam at ITN 2.5 MeV Van de Graaff PIXE setup. A Si(Li) detector placed at 110º and a CdTe detector placed at 70º, both relative to the beam direction were used. A detail disprection is presented elsewhere [4,5]. A movable 1.5 μm Al- foil is usually located in front of the beam before it enteres in the irradiation chamber. In two of the experimental settings this foil was removed to eliminate an eventual influence of the 10 keV beam energy scattering introduce by this diffuser. The beam quality when no Al-foil was used, was checked on a quartz disc that exists in the chamber back end. In each experiment various ion beam energies were used to irradiate the three W compounds. For each ion beam energy value spectra with good statistics (close to 1000000 counts on the W-L α , or 8000 counts on the W-K α ) were collected. The details for each of experiments are presented in table 1. Table 1: Description of the five experimental conditions used. a.p.e. means that all previous energies were studied within the energy range defined except 2.155 (3rd) and 2.245 (3rd), 2.13 (4th) and 2.22 (4th). 1st 2nd 3rd 4th 5th Incident angle (º) 15 22.5 22.5 22.5 45 Al-foil No Yes Yes No No Energy range (MeV) 1.75-2.50 1.50-2.40 1.50-2.25 1.50-2.25 1.86-2.40 Steps (keV) 125 90 a. p. e. a. p. e. 180 Si(Li) detector Yes Yes Yes Yes Yes CdTe detector No No No No Yes