Capabilities of miniature high resolution X-ray spectrometer on ion microprobe

Division of Experimental Physics,Ruđer Bošković Institute, Bijenička cesta 54, 10000-Zagreb, Croatia

Particle induced X-ray emission (PIXE) technique is widely used as a routine tool for elemental concentration determination in samples irradiated with MeV energy protons. Although small variations of X-ray intensity ratios or energies due to chemical effects can be observed with energy dispersive detectors like Si(Li), Ge and/or SDD [1], they are usually ignored. Using wavelength dispersive spectrometers fine structure of X-ray spectra is revealed, clearly showing chemical effects and setting ground for chemical speciation applications. Recently we employed simple high energy resolution crystal X-ray spectrometer to study chemical effects on broad beam PIXE induced Kβ X-ray spectra of 3d transition element compounds [2, 3, 4, 5]. Based on the experience gained with broad beams, we designed and constructed downsized wavelength dispersive X-ray (WDX) spectrometer for application on microscopic samples utilizing micrometer beam size available at our ion microprobe. Development of the spectrometer included several stages: optimization of spectrometer geometry with X-ray tracing program XTRACE [6, 7], design of dedicated vacuum chamber housing flat crystal, sample holder and charge coupled device (CCD) as X-ray detector and development of image processing procedure for transfer of X-ray images to energy dispersive spectra. In this work we will describe our system and each construction step followed by discussion about its advantages and limitations. Effect of chemical environment on high resolution Kα and Kβ spectra will be shown for several silicon compounds and silicates irradiated with 2 MeV protons. Same compounds are used to study variations of intensity distributions in Kα satellites induced with 20 MeV carbon ions. Spectrometer capability to distinguish sulphate from sulphide compounds based on chemical effects on Kβ sulphur spectra will be presented. We will also demonstrate ability of spectrometer to separate K and M X-ray lines which are usually irresolvable with energy dispersive detectors.

[1] S. Fazinić, I. Božičević Mihalić, L. Mandić, J. Anal. At. Spectrom. 28 (2013) 1725  
[2] S. Fazinić, M. Jakšić, L. Mandić, J. Dobrinić, Phys. Rev. A 74 (2006) 062501
[3] L. Mandić, S. Fazinić, M. Jakšić, Phys. Rev. A 80 (2009) 042519.
[4] S. Fazinić, L. Mandić, M. Kavčič, I. Božičević, J. Anal. At. Spectrom. 26 (2011) 2467
[5] S. Fazinić, L. Mandić, M. Kavčič, I. Božičević, Spectrochim. Acta, Part B 66 (2011) 461-469.
[6] T. Tadić, M. Jakšić, I. Božičević, X ray Spectrom. 38  (2009) 222
[7] T. Tadić, M. Jakšić, I. Božičević, X ray Spectrom. 40 (2011) 147