Development and Evaluation of Novel Structured Scintillation Detector.

摘要

In recent years, composite scintillators embedding small size inorganic crystals in an organic matrix have been actively developed. One of the major concerns in these type of detectors is optical transparency. Due to the refractive index mismatch between the host and the crystals, nanosize inorganic crystals have to be used. One way to produce nanosize inorganic crystals is by wet milling, which involves grinding the inorganic crystals in an organic solvent. Milling is relatively simple in terms of preparation and equipment, but it is also known to introduce defects in the ground materials. In this work, a novel light yield measurement technique and a lifetime measurement system are developed to evaluate how milling changes the performance of inorganic crystals. The light yield measurement technique is applied to milled BaFCI:Eu inorganic crystals. The crystals were milled in a tributyl-phosphate and cyclohexane mixture, where the tributylphosphate was the ligand and cyclohexane was the solvent. It was found that the light yield of the milled crystals decreases to 0.17% of the bulk light yield when the crystals are at a mean size of 1375 nm. For smaller particles at a mean size of 292 nm, the light yield increases to 1.8% of the bulk. To qualitatively investigate the cause of the change in light yield, a lifetime measurement system was constructed. However, the high voltage of the X-ray tube fluctuated due to an abnormally high leakage current, and thus lifetime measurements on the milled crystals were not performed.