Scintillators are converters from ionizing radiation to visible photons. Below is a schematic drawing. Ionizing radiation has a ahigh penetarting power and we cannot observe it directly. However, once radiation is converted to visible photons, we can observe and analyze iteasily.
Generally, the term scintillator means a single crystal. However, recent technical progress enables us to utilize transparent ceramic scintillators.
Although it is difficult to obtain fully transparent ceramic materials, it has some advantages to single crystals, such as an uniform doping of emission centers, high mechanical strength, large size, and low cost. Below figures show emission and transmittance spectra of transparent Ce doped YAG with different Ce concentrations.
We (T. Yanagida and Konoshima Chemical Co. Ltd.) are developing transparent ceramic scintillators to apply them to industrial applications. Main targets are garnet and sesquioxide doped with some emission centers.
PL spectra of Ce:YAG (left) and transmittance spectra of Ce:YAG (right).
There is no scintillator to satisfy below erquirements perfectly. We must select adequate scintillator for each appliaction.
In addition to scintillators, I study about photodetectors. Conventionally, photomultiplier tube (PMT) is used to convert scintillation photons to electrons. Recently, Si-based semiconductor photodetectots are also candidates. Especially, Si avalanche photodiode (Si-APD) and Geiger mode APD have an internal gain so that they can be applicable for scintillation photono detection. Also I' m interested in using wide bandgap semiconductor for photodetector applications. Examples of wide gap semiconductor are GaN and diamond which have a high quantum efficiency to VUV-UV photons.
ELiCaAlF6 scintillator for neutron detection (Tokuyama corporation,left)
EGAGG scintillator (Furukawa Co. Ltd., center)
EPulse X-ray streak camera system (Hamamatsu Photonics, right)
Graduate school of materials science, Nara institute of science and technology
Takayuki Yanagida
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