Zone Refining of Raw Materials for Metal Halide Scintillator Crystal Growth

In recent years, scintillators have been researched for homeland security applications where properties such as high light output and low energy resolution are required for efficient gamma ray spectroscopy. Several promising scintillators, including SrI₂ [Strontium Iodide], CsSrI₃ [Cesium Strontium Iodide]_, and KSr₂I₅ [Potassium Strontium Iodide] are activated with EuI₂ [Europium Iodide]. The quality of EuI₂ raw material is generally poor and inconsistent as-received from the manufacturer. Material purity is known to affect its scintillation performance, and so purification processes have been investigated to improve the performance of Eu-doped [Europium-doped] scintillators. In this work, zone refining is explored as a method to purify EuI₂ while ICP-MS [Inductively Coupled Plasma Mass Spectroscopy], DSC [Differential Scanning Calorimetry], and scintillation performance are used to determine the effectiveness of the treatment. It is seen that zone refining results in effective purification of the material at the center of the charge, as expected. Comparison of the light output and energy resolution of the as-received EuI₂ with that of EuI₂ from each of the refining batches indicates that refining EuI₂ greatly improves the performance of the material. Based on experience gained during this investigation, a miniature zone refining furnace was designed and constructed to enhance future refining efforts.