TECHNIQUES FOR PRODUCTION OF ORTHOSILICATE SCINTILLATORS

本课题的目标是开发高产、低成本生产高性能掺铈氧化硅酸镥（LSO）闪烁晶体的新方法。LSO是近五十年来发现的最有前途的新闪烁体之一，具有x和伽马射线光谱学的重要特性的独特组合，即：高密度，快速衰变，相对于BGO的大光产率。LSO似乎是PET系统中替代BGO的主要候选材料。然而，由于所采用的高温，晶体生长（Czochralski法）方面的困难阻碍了LSO的实际利用。在第一阶段的努力中，我们成功地完成了一项可行性研究，验证了使用新的低温晶体生长技术生产闪烁LSO晶体的创新方法。制备了体积为几mm3的透明多晶LSO样品，并对其材料性质、闪烁性质和对伽马射线的响应进行了研究。新晶体的性能与用Czochralski法生长的高质量晶体相比较良好。在第二阶段，我们将优化生长技术并简化工艺，以获得专门适合PET探测器环的大体积，高性能和低成本的LSO闪烁晶体。为了实现这一目标，我们还将开发和实施新的铸造技术，直接为当前的PET仪器生产具有正确尺寸的矩形晶体和晶体块。最后，我们将建立一条预生产线，并使用第一阶段建立的评估技术评估生长晶体的产量和质量。拟议的商业应用：迄今为止，LSO仍未商业化。当可用时，它将在应用程序主机中广泛使用，从而立即获得性能提升，或者在需要快速计时或高计数率的情况下启用全新的用途。这些包括：PET；高能物理;工业过程控制；环境监测;地球物理学;以及APD等固态光电探测器和新型漂移光电探测器的全新用途。

The goal of this proposal is to develop novel methods for high-yield, low- cost production of high performance cerium-doped lutetium oxyorthosilicate (LSO) scintillating crystals. The motivation is that LSO is amongst the most promising new scintillators discovered in almost five decades, with a unique combination of important properties for x and gamma-ray spectroscopy, namely: high density, fast decay, and large light yield relative to BGO. LSO seems to be a prime candidate to replace BGO in PET systems. However, the practical utilization of LSO is hindered by difficulties related to crystal growth (Czochralski method) due to the high temperatures employed. During the Phase I effort we successfully concluded a feasibility study which validated the innovative approach using a new low-temperature crystal growth technology to produce scintillating LSO crystals. Light transparent polycrystalline LSO samples of a few mm3 in volume were grown and investigated for their material properties, scintillation properties and response to gamma-rays. The properties of the new crystals compared well with high-quality crystals grown by the Czochralski method. In Phase II we will optimize the growth technique and streamline the process to obtain large volume, high performance and low cost LSO scintillating crystals specifically suited for PET detector rings. Towards this goal we will also develop and implement novel casting techniques to directly produce rectangular crystals and blocks of crystals with the correct dimensions for current PET instruments. Finally we will set-up a preproduction line and evaluate yields and quality of the grown crystals using evaluation techniques established in Phase I. PROPOSED COMMERCIAL APPLICATIONS: To date LSO is still not commercially available. When available its use will be widespread in hosts of applications leading to immediate performance gains, or enabling completely new uses where fast-timing or high counting-rate is needed. These include: PET; high-energy physics; industrial process control; environmental monitoring; geophysics; and space instrumentation etc., as well as brand new uses with solid-state photodetectors such as APD's and new drift photodetectors.