On this page:
- Multi-Mode and High Resolution Imaging Plates
- New Ceramic Scintillators
- 1D and 2D Dosimetry
- Related Links
Andy Edgar | Grant Williams
There has been a revolution in X-ray imaging in the last twenty years, with traditional photographic film/phosphor methods being replaced by digital techniques, including storage phosphor, CCD/phosphor, CMOS/phosphor and photoconductor array methods.
Storage phosphors based on the photo-stimulated luminescence effect offer many advantages over film, but suffer from inferior spatial resolution. The problem lies in the light scattering from the powder grains of the storage phosphor (usually BaFBr:Eu). This problem rules out storage phosphors for mass radiography applications such as mammography.
Our research into nano-structured materials such as glass ceramics and polymer-nanocrystal composites seeks to combine good storage phosphor properties with high transparency.
Our objective for dual-energy plates is to make screens which can record not only the shadow image of an object for polyenergetic X-rays, but also the division of the image into separate energy bands. In practice, the image will be recorded for just two different X-ray energies, but this will yield invaluable information on the chemical content of the object being imaged, since elements with small atomic numbers are much more transparent to X-rays than those with high atomic numbers.
We are also working on stratified imaging screens which can distinguish neutron from gamma and x-ray radiation, and single mode plates for high resolution. The materials we work with include transparent glass ceramics and crystal-resin composites.
Research and development of fast and cost effective ceramic scintillator materials.
Murray Bartle | Andy Edgar
Scintillators are used for dynamic radiation imaging, therefore scintillator imaging requires a material with a fast response and short decay times.
We aim to produce a fast but cost effective ceramic scintillating material with low afterglow, for applications such as PET (Positron Emission Tomography - a high-tech medical imaging technique).
We are also developing new efficient red-emitting scintillators which are better matched to semiconducting detectors than the traditional photomultipliers. The emphasis is on novel materials which combine nano or microstructures with high transparency and therefore optimal scintillation efficiency.
We are primarily researching rare-earth doped inorganic materials such as heavy-metal oxides and halides, but organic scintillators are also under investigation. Lithium and boron containing compounds for applications to neutron detection are also being researched.
Grant Williams | Sebastiampillai Raymond
Current radiation dosimeters are based on ionization gauges, solid state or thermo-luminescent devices.
The first two methods provide an immediate electronic reading but are expensive. The third provides a record of the cumulative dose, but read-out is destructive, since it requires the material to be heated to thermally excite trapped carriers with measurement of the resultant thermo-stimulated-luminescence.
There is clearly a need for an all-optical radiation dosimeter that can retain a record of the radiation dose for an extended period of time, then have the dose information optically erased. Such a dosimeter would have the advantage of requiring only one readout device with many different reusable detectors.
We focus on human-tissue-equivalent dosimeters, high dose range dosimeters, fibre-optic dosimeters, 2D dosimeters and semi-permanent storage phosphor imaging plates. We have begun polymer/crystallite research using existing polymers and resins where the refractive index is closely matched to the micron-sized crystallites. The crystalline materials of interest are primarily single crystal and polycrystalline perovskites doped with manganese or rare earth metals, and composites based on resin-crystal mixtures.
Radiation Instrumentation and Consulting:
X-ray imaging resources:
- A Practical Course in Reference Dosimetry
- Dosimetry for X-Ray Users
- NIST Radiation Interactions and Dosimetry Group