A new life for the wavelength-dispersive X-ray spectrometer (WDS): incorporation of a silicon drift detector into the WDS for improved quantification and X-ray mapping

Abstract

Abstract. The wavelength-dispersive X-ray spectrometer (WDS) has been around for a long time and the design has not changed much since its original development. The electron microprobe operator using WDS has to be meticulous in monitoring items such as gas flow, gas purity, gas pressure, noise levels of baseline and window, gas flow proportional counter (GFPC) voltage levels, count rate suppression, anode wire contamination and other detector parameters. Recent development and improvements of silicon drift detectors (SDD's) has allowed the incorporation of a SDD as the X-ray detector in place of the proportional counter (PC) and/or gas flow proportional counter (GFPC). This allows minimal mechanical alteration and no loss of movement range. The superiority of a WDS with a SDD, referred to as SD-WDS, is easily seen once in operation. The SD-WDS removes many artefacts including the worse of all high order diffraction, thus allowing more accurate analysis. The incorporation of the SDD has been found to improve the light and mid element range and consequently improving the detection limit for these elements. It is also possible to obtain much more reliable results at high count rates with almost no change in resolution, gain and zero-peak characteristics of the energy spectrum. IntroductionThe electron probe microanalyser (EPMA) instrument has been around for a long time, which utilises the X-ray microanalysis techniques of wavelength-dispersive and energy-dispersive X-ray spectrometry (WDS and EDS). The WDS design has not changed much since its original development. WDS exhibits far better spectral resolution than the conventional EDS. The combination of EDS and WDS produces a very powerful analytical technique allowing for excellent quantitative X-ray mapping (QXRM). However, the electron microprobe operator using WDS has to be meticulous in monitoring items such as gas flow, gas purity, gas pressure, noise levels of baseline and window, gas flow proportional counter (GFPC) voltage levels, count rate suppression, anode wire contamination and other detector parameters.Over the last couple of years we have been developing and testing alternative configuration WD spectrometers, using Amptek PIN (p-intrinsic-n type diode) and silicon drift detectors (SDD's) in place of the sealed proportional counter (SPC) and gas flow proportional counters (GFPC's) respectively.

TEXS: in-vacuum tender X-ray emission spectrometer with 11 Johansson crystal analyzers

“…Historically, flow proportional counters were mounted in wavelength-dispersive spectrometers for micro-analysis at electron microscopy stations (e.g. 42 for a recent overview).…”