Energy non-linearity effects in the response of ionic crystal scintillators to X-rays with energy in the region of the K-absorptions edges: experimental results

The response of a YAP, NaI(Tl) and BaF2 scintillators to X-rays with energies around the Y, I, and Ba K-absorption edges, respectively, was investigated. For all the scintillators, the amplitude response follows different linear trends for X-ray energies below and above the respective K-edges, presenting a discontinuity at these energies. An abrupt decrease of about 3%, 5% and 2% were observed in the detector amplitude at the K-edges, for the YAP, the NaI(Tl) and the BaF2 scintillator, respectively, corresponding to a decrease of 0.5±0.1, 1.7±0.3 and 0.8±0.2 keV in the energy calibration line. These discontinuities result in a region within 0.5±0.1, 1.6±0.3 and 0.9±0.2 keV where the X-ray energy cannot be obtained unambiguously. The scintillation yields for X-rays present abrupt decreases of about 3%, 4% and 2%, respectively, at the K-edges. The measured non-linearity effects are significantly larger than those obtained for gaseous and semiconductor detectors. The higher amplitude non–linearity observed in NaI(Tl) is attributed to the larger light yield non-linearity in the electron response of this crystal.