A von Hamos-Type Parallel Collection Wavelength Dispersive Spectrometer for Microbeam Analysis

Abstract

Wavelength dispersive spectrometers (WDS) of the Johann and Johannson types are used in microbeam analysis of samples in the (TEM).^(1,2) A proportional counter (PC) is usually used as a collector of x-ray quanta in WDS. Such spectrometers have a reasonably good geometrical aperture of the order of Ω/4π ≃ 10^-3, where Ω is the solid angle of effectively reflecting area of a crystal. They have good spectral resolution (Δλ/λ ≃ 10^-3), but they are not parallel detectors, i.e., they cannot simultaneously measure the intensities of different spectral lines. Taking into account scanning across the spectra, the real aperture of a Johann spectrometer is approximately 10²–10³ times less. A quantitative interpretation of spectra for thermally or radiation-changeable compounds (or alloys of low and high vapor pressure elements) is difficult for such spectrometers.