The Scintillation Materials Research Center at the University of Tennessee will carry out research that addresses a critical need in national security. Currently the ability to detect radioactive materials at border crossings and ports of entry is limited by the availability and cost of the materials that are used as radiation sensors. This research will address fundamental aspects of manufacturing technology that directly impact the affordability of the high performance detection materials that are needed for effective high speed scanning of cargo. Innovative synthesis techniques will be developed with the goal of improving the sensitivity and lowering the cost of materials that have the capability of uniquely identifying specific nuclear threats. If successful, this technology will yield improvements in both efficiency and sensitivity of nuclear threat detection as well as significant increases in availability and affordability. The same nuclear detection technology is likely to also find applications to other areas serving the public interest including nuclear medicine and sensors used in the exploration for energy reserves.
Specifically, the Scintillation Materials Research Center will address a grand challenge in radiation detection by developing crystal growth technology aimed at enabling the production of large size (> 1 cubic inch) gamma-ray scintillators with less than 1% energy resolution at 662 keV. The properties of currently available detection materials limit the performance of radiation detection systems. For most gamma and neutron detection applications, these materials must be available in large size at a reasonable cost while maintaining the required energy resolution to unambiguously identify various nuclear signatures. For gamma-ray and neutron detection applications, scintillators currently offer more options for room temperature operation and large-scale production while semiconductors tend to have better energy resolution. New fundamental understanding of the materials properties of recently discovered scintillators will be coupled with numerical simulations of fluid flow and heat/mass transport to drive the design of new crystal growth furnaces and new growth protocols aimed at demonstrating the potential of large scale production. The effort will focus on recently discovered scintillators that appear to have inherent advantages for large-scale production. A key strategy of the program is the tight integration of research and education that will provide opportunities for students to develop a deeper knowledge, expertise, and appreciation of this important field.
The goal of this project is to demonstrate practical manufacture of selected novel materials in crystalline form. The selection process involves evaluation of their potential for gamma-ray sensitivity and ease of synthesis in a size of 1 cubic inch as required by the Global Nuclear Detection Architecture. The project is focused on cost-effective scale-up process development of high quality scintillation crystals for practical applications. Such materials are used as sensitive radiation sensors and therefore can significantly enhance security from nuclear threats via monitoring illegal transportation of radioactive materials t the national borders. In addition, scintillators can benefit other areas by: a) improving early stage diagnosis of cancer via recording the images of internal organs generated by radiation and indicating location of cancer tumors with excellent resolution and accuracy, and b) providing availability of new energy resources via improving geophysical exploration. Our comprehensive technical approach included material characterization followed by the development of innovative and unique crystal growth furnaces and growth protocols specifically designed to optimize the quality, size, and cost of selected scintillators. The activities included studying materials properties (structural, thermodynamic) and determining the impact of material properties on furnace design and growth protocols, which helped us to identify key parameters of melt growth technology. Thus, via the use of an optically transparent growth furnace, we were able to in-situ visualize and document micro-scale growth processes, such as solidification mechanisms and the defect evolution, which are otherwise hidden by layers of insulation in conventional growth furnaces. Examples of single crystals of scintillation materials are shown in the pictures: crystal is grown via crystallizing molten mixtures in furnace (left), synthesized samples are optically clear (middle); crystals scintillate, i.e. produce visible light under excitation with ionizing radiation such as gamma-ray or neutrons (right). Although our proposed project focuses on fundamental science guided by homeland security and industrial interests, an important additional benefit is to train new generation researchers in the area of materials synthesis. Crystal growth is a field of scientific endeavor that has been identified by the National Research Council www.nap.edu/catalog.php?record_id=12640) as an important area in which training opportunities are limited; radiation detection materials are an important subset of crystalline materials for which there are also few educational opportunities. During this project, three graduate students (two PhD and one MS) and three undergraduate students have been trained in such areas as material design, hands-on crystal growth, development of growth protocols, numerical modeling of crystal growth processes, and a variety of materials characterization techniques. The work has also motivated undergraduate students to do materials science and engineering research through hands-on experience with various interdisciplinary techniques.
