Positron Emission Tomography (PET) has been developed into a new and potent diagnostic and research tool for modern medicine. The performance of this tool depends critically on the effectiveness of the scintillator material that converts the ionizing radiation into measurable light at optical wavelengths. Such materials must satisfy a number of stringent criteria in order to be useful for such applications, including high stopping power for ionizing radiation, high light output per absorbed particle, ultrafast (nanosecond) decay times, and the ability to be fabricated economically into transparent chemically stable components. While a limited number of materials now exist that function acceptably as scintillators, none of them are able to satisfy all the desired criteria. Many are not bright enough; some are hampered by a persistent long-lifetime component that clouds the measurement; others are chemically unstable or hygroscopic; and almost all are difficult to fabricate, requiring painstaking and difficult crystal growth techniques. We have identified a new class of materials, activated optical ceramics, as candidates to fill this urgent and growing need. These appear to have all the desirable characteristic: higher density than any material currently used as scintillators; and activator (Ce3+) with one of the shortest decay items; high efficiency under high-energy (CRT) excitation; and a simple and inexpensive means for fabrication by powder processing techniques. All these properties have already been demonstrated in analogous forms, and should be equally appropriate for scintillator applications. A research program is proposed to explore the potential of activated optical ceramic for scintillator applications. This program will involved a comprehensive investigation of the mechanisms that govern the scintillation process and the manner in which the are affected by the material properties of these ceramics. Initial measurements will be made on unconsolidated powders, to quantify the brightness and speed of their emission and the efficiency of the all-important energy transfer step that enables the individual high energy particles to be transformed into a detectable shower of optical photons. Spectroscopic measurements will be done under both optical and ionizing excitation, and over a wide temperature range, to enable a definitive characterization of the individual steps in the total scintillation process. These measurements will also identify the most promising material candidates, which will then be developed more intensively, including a ceramics effort to demonstrate the feasibility of component fabrication. This new technology of activated optical ceramics offers unique opportunities for scintillator development. Building on our substantial background in the scintillator field, we have every reason to believe in the ultimate success of this effort.
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