The radiation detection market is one that does not shift quickly to the use of new materials, but there are signs of acceptance for new materials that can provide advantages in terms of cost, performance, and availability. Changes are happening in scintillators and semiconductors to detect X-ray and gamma radiation, as well as neutron detection materials.
Continuing Efforts to Replace Helium-3 for Neutron Detection
The crisis that motivated research into replacements for 3He has somewhat abated, as restrictions on the use of the material have been effective in extending the supply for applications that absolutely require it. The U.S. Department of Energy (DOE) is supplying about 6,000 liters/year of 3He for scientific research, domestic security, and medical applications. Also, development of alternative materials has led to a decrease in demand for 3He.
That said, the need for better neutron detectors that do not use 3He continues. Neutron detection is important in domestic security, military, oil and gas, and nuclear power applications, where the use of 3He remains restricted.
The best option for replacing 3He in large radiation detection portals has been 10B-lined tubes, which have the right combination of detection efficiency and gamma radiation sensitivity and can act as a drop-in replacement for 3He. The first generation of neutron detection materials based on 6Li are efficient in detecting neutrons, but do not work as well in the presence of strong gamma radiation.
Improvements in materials are on the way, including:
- Development of 10B-based solutions that can use less material while maintaining efficiency matching that of 3He
- Materials using 6LiF for improved performance, including notably 6LiF/ZnS solutions that are commercially available and gaining acceptance
- Materials based on compressed noble gases, which promise a low-cost, high-performance option
Improving Performance and Reducing Cost of Scintillation and Semiconductor Materials
As with nearly any engineered material, the goals for radiation detecting materials are improving performance and reducing cost, two things that can seem to be mutually exclusive but which both need to occur in order for customers to transition from an existing material to a newer one.
The drive to replace legacy materials has led suppliers to consider a vast number of candidates, from simple salts to semiconductors. The market for radiation detection materials can be divided into four categories:
Established, commercially successful materials such as NaI, CsI, LSO, and LYSO. This is a category where we expect to see continued demand, because the materials have demonstrated sufficient performance and the end applications are in growth industries. These materials should experience modest growth. HPGe may be considered part of this category, because there are applications that demand its high resolution despite its high cost, and improved cryogenic cooling methods are making it more attractive for mobile applications.
Newer materials such as LaBr3, CLYC, CZT, and SrI2. These materials promise improved performance over the established materials in certain areas, but still have obstacles to overcome in order to achieve commercial success. There is opportunity for tremendous growth if such materials overcome their challenges in performance and cost, but also the possibility for commercial failure if they do not.
Lanthanum bromide was the first scintillation material on the market with better resolution than NaI. It is seeing increased adoption, but its high cost is a concern. CYLC holds the promise of the ability to detect both gamma radiation and neutrons, but performance has fallen somewhat short of expectations and its future as a gamma detector is in no way guaranteed. CZT is very promising, but manufacturing yields still need to come up and costs need to come down, which will not be easy to achieve. Strontium iodide is a wild card that is trying to gain commercial acceptance but faces real challenges in producing large enough crystals that do not suffer from self-absorption and reduced resolution.
Older materials that are used in scientific research or in niche commercial applications. These are mostly fluoride- and oxide-based materials that will continue to be used to some extent but may eventually be replaced by higher performing options.
Experimental materials, including various salts, ceramics, and semiconductors. These materials are far away from commercialization and many appear quite esoteric. Some may see some commercial use by the end of our eight-year forecast period, some may continue to be used in research quantities, and others will likely be deemed unsuitable and die away. The most promising materials in this category are ceramics, which hold the promise of manufacturing sufficiently large polycrystalline ingots of materials that are promising scintillators but cannot easily be grown in single crystal form.
Benefits of and concerns about rare earth metals.
Many scintillation materials make use of rare earth elements. Rare earth metals are desirable in radiation detection because of their high Z values and therefore excellent stopping power for gamma rays. Europium and cerium are common activators in scintillation materials. There is also interest in scintillators based on rare earth metals, and a great variety of these have been synthesized in laboratories. LBNL is currently involved in an extensive research project to evaluate lutetium-based scintillators for medical applications.
There are potential supply issues with rare earth metals, however, that are causing some scintillation materials suppliers to look to alternatives that do not contain lutetium or lanthanum. The National Institutes of Health is currently funding a project titled, “Lu-free Scintillators for PET.” Many rare Earth metals have been either predominantly or entirely produced in China, and Chinese export quotas have given some cause for concern. Increased mining in countries outside of China since 2013 has eased supply issues, though, and China’s agreement to end quotas is encouraging.
In the end, raw material prices might not change much. Overall, n-tech Research expects that raw materials for scintillators will be available in sufficient quantities to meet even the greatest foreseeable demand, at least in the near term. Still, long-term efforts to diversify the range of potential scintillator materials and mitigate the effect of future materials shortages may be wise.