Scintillators coupled to optical detectors such as photomultiplier tubes are the most common detectors in medical imaging systems. Applications range from the ubiquitous X-ray diagnostic imaging to the more sophisticated X-ray CT scanning to the esoteric nuclear medicine systems such as PET and SPECT. Additionally, similar devices are being used by Homeland Security for the detection of radioactive materials to mitigate external threats. Important requirements for scintillator materials include high light output, high stopping efficiency for the incident radiation, and fast response. Minimal afterglow, stable performance, low cost, and good linearity are also important.
Ceramic scintillators are polycrystalline bodies composed of simple inorganic compounds such as metal oxides or halides, whose grains, typically a few microns or less in size, are bonded together by high temperature processes, usually greater than 1500°C. In addition to scintillators, these transparent optical ceramics (TOCs) have also found use as IR raydomes for missile guidance systems, laser hosts, and transparent armor (windows for military vehicles). In order to be useful for scintillators, transparency (or at least high translucency) is required so that the light generated by the incident ionizing radiation will be able to emerge and be detected photo electronically. An example of a TOC scintillator, activated with Ce, is shown to the left.
(Gd,Lu,Ce)3(Al,Ga)5O12 Garnet TOC ceramic scintillator produced by RMD
Ceramics offer the following prospective advantages compared to single crystal scintillators:
- Increased flexibility in scintillator composition, since precursor powders can be tailored to provide specific needed properties.
- Lower processing temperatures, since a melt, typically required for crystal growth, is avoided, potentially lowering costs by increasing yields
- Faster processing cycles, hours compared to days
- Near net shape fabrication, reducing machining costs and providing the ability to produce complex shapes if required.