Blue bottles7 December 2011
A Japanese company has developed new radiation-fluorescent plastic, which could cut the production costs of scintillators, the core material used in radiation detectors.
Scintillation-based radiation detectors currently represent more than 70% of the radiation detector market, and will remain the only cost-effective solution in may cases, according to an August 2011 report from market research company NanoMarkets. Sodium iodide has been the industry standard for scintillation detectors, but is very fragile and moisture-sensitive. Users are looking for systems to provide better light output and linearity as well as energy resolution. NanoMarkets therefore believes that there will be strong demand for detectors based on novel materials such as oxides, simple salts, silicates and plastics over the next eight years.?The new material may fulfil these requirements.
Scintirex is based on the resin used in plastic drinking bottles, polyethylene terephthalate (PET/PETE). Studies have found that PET bottles are well suited to radiation measurement and light propagation. The material is also easy to fabricate and mould, so radiation detectors can be made in many different shapes and sizes. In addition, the widespread use of PET means that Scintirex has a low production cost compared to other types of plastic scintillators.
Scintirex has been developed by Teijin Chemicals in cooperation with Kyoto University Nuclear Reactor Research Institute and the National Institute of Radiological Sciences in Japan. Teijin, which will begin supplying Scintirex from September 2011, claims that the material will slash the production cost of scintillators to one-tenth, or less, of current levels.
Organic scintillators were developed about 60 years ago to detect radiation. Scintillator performance is measured by the number of easy-to-measure deep-blue (visible frequency) photons emitted per incident radiation event. To obtain high scintillation performance, organic scintillators are manufactured by mixing plastic with chemical additives such as wavelength shifters. However, because the manufacturers keep the detailed information regarding the types and quantities of the wave shifters confidential, organic scintillators are extremely expensive. 
In addition, a special grinding process performed on the surface of plastic scintillators to efficiently detect the light they generate thwarts cost reductions through mass-production.
In May 2010 researchers lead by Dr. Hidehito Nakamura, Assistant Professor, Kyoto University, Nuclear Reactor Research Institute, demonstrated that a simple plastic bottle could be used as an organic scintillator. PET bottle resin, however, emits fewer photons than a conventional organic scintillator and the ultraviolet photons emitted are difficult to measure.
This prompted further research to develop a radiation-sensitive plastic without wave shifters. Researchers selected monomers to determine the molecular structure of the radiation-sensitive plastic and modified the various types of polymerization catalysts to surpass the performance of plastic scintillators with a molecular structure similar to that of the plastic resin of PET bottles: polyethylene naphthalate. As a result, the team overcame the fluorescence level weakness of PET bottle resin (by a factor of five).
A recent study has compared the qualities of Scintirex with plastic scintillators from Company S. The results indicated that the performance of Scintirex is equivalent or superior to plastic scintillators (see table).
The newly developed radiation-sensitive plastic can be used as a direct replacement of current plastic scintillators, according to Teijin Chemicals. Detectors equipped with Scintirex could be used for radiation management at nuclear power plants, nuclear fuel processing facilities and radiation stations, such as those in hospitals. The material also has a wide array of other applications, including radiation-inspection equipment at airports, harbours, rail stations and aerospace hardware.
If radiation-sensitive plastic could be used in larger quantities, it is likely that the production of devices never before available could become feasible through use of a high-speed, high-sensitivity method. These might include walk-through contamination monitors (which can measure the contamination of many local residents, or nuclear power plant workers in real time), drive-through truck monitors (which measure trucks and work vehicles in real time), as well as whole-body counters (until now a separate detector has been used).
This article was originally published in the November 2011 issue of Nuclear Engineering International magazineTablesTable 1