Investigation of high-resolution superconducting tunnel junction detectors for low-energy X-ray fluorescence analysis

The energy resolution of conventional semiconductor detectors is insufficient for simultaneously separating the leading fluorescence lines of low Z and medium Z materials in the soft X-ray regime. It is therefore important to investigate alternative detection instruments offering higher energy resolution and evaluate their applicability to soft X-ray fluorescence (XRF) analysis. In this paper, various results of the characterization and evaluation of a cryogenic superconducting tunnel junction (STJ) detector, which was provided to the Physikalisch-Technische Bundesanstalt (PTB) by the Lawrence Livermore National Laboratory, are given with respect to both detector response functions and XRF. For this investigation, monochromatized undulator radiation of high spectral purity, available to the PTB X-ray radiometry laboratory at the electron storage ring BESSY II, was employed, by which it was possible to record the STJ response functions at various photon energies of interest ranging from 180 to 1600 eV. By scanning the effective detector area and the adjacent substrate and leads, relevant artefacts of the detector response were identified.