Measuring conditions for second order X-ray Bragg-spectrometry

The KL_2,3 (α)_1,2-lines of ¹⁹K, the L₃M_4,5 (α)_1,2-lines of ⁴⁸Cd, and the M₅N_6,7 (α)_1,2-lines of ⁹²U are lines of comparable energy in the region of approximately 3 keV. In none of these cases were we able to resolve the three doublets when recording the spectra in first order Bragg spectrometry using a PET crystal as the dispersing element. For the purpose of enhancing the resolving power of the spectrometer, the three α spectra were recorded in second order reflection, thereby transferring the lines into another spectral region dominated by X-ray quanta of half the energy. In order to achieve high net peak intensities as well as a high peak-to-background ratio and, consequently, a high level of detection capability, the discriminator settings should be optimized quite carefully. In this manner, we were able to resolve the three α doublets and estimate α₂/α₁ intensity ratios. Inexplicably, current monographs, e.g., by Goldstein et al, do not contain any indications about the rational use of high order spectrometry. Only a few rather old monographs contain some hints in this regard