The hard X-ray response of Ce-doped lanthanum halide scintillators

We summarize the results of a number of hard X-ray measurements on cerium-doped LaCl3 and LaBr3 scintillators. The experiment was carried out at the HASYLAB synchrotron radiation facility using highly monochromatic pencil beams across the energy range 10.5–100 keV. Additional full-area measurements were carried out using radioactive sources. All measurements were carried out at room temperature. The measured FWHM energy resolutions (ΔE/E) under pencil beam illumination were 29% (LaBr3) and 32.4% (LaCl3) at 10.5 keV falling to 7.8% (LaBr3) and 9.2% (LaCl3) at 100 keV. At 662 keV, the energy resolutions were 3.9% and 3.0% FWHM. The proportionality of the energy responses shows marked deviations from linearity above and below the La edge at 39.8 keV. At the edge the energy response changes by 3%. Fine structure across the edge was also investigated using single photon count rate measurements taken in 1 eV steps across the edge. The data show considerable near-edge structure when compared to curves generated from standard atomic data tables. However, very little evidence was found for extended X-ray fine structure suggesting that the bulk of the structure arises from the local coordination environment.