Recent research in the field of phosphor and scintillator materials and related detectors is reviewed. After a historical introduction the fundamental issues are explained regarding the interaction of x-ray radiation with a solid state. Crucial parameters and characteristics important for the performance of these materials in applications, including the employed measurement methods, are described. Extended description of the materials currently in use or under intense study is given. Scintillation detector configurations are further briefly overviewed and selected applications are mentioned in more detail to provide an illustration.

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Scintillation detectors for x-rays

Due to events of the past two decades, there has been new and increased usage of radiation-detection technologies for applications in homeland security, nonproliferation, and national defense. As a result, there has been renewed realization of the materials limitations of these technologies and greater demand for the development of next-generation radiation-detection materials. This review describes the current state of radiation-detection material science, with particular emphasis on national security needs and the goal of identifying the challenges and opportunities that this area represents for the materials-science community. Radiation-detector materials physics is reviewed, which sets the stage for performance metrics that determine the relative merit of existing and new materials. Semiconductors and scintillators represent the two primary classes of radiation detector materials that are of interest. The state-of-the-art and limitations for each of these materials classes are presented, along with possible avenues of research. Novel materials that could overcome the need for single crystals will also be discussed. Finally, new methods of material discovery and development are put forward, the goal being to provide more predictive guidance and faster screening of candidate materials and thus, ultimately, the faster development of superior radiation-detection materials.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400030016

Radiation Detector Materials: An Overview

The luminescent properties of 1 mol % Eu3+-doped cubic Lu2O3 nanocrystals prepared by a combustion synthesis route were investigated. The visible emission spectrum of the europium doped Lu2O3 nanocrystals indicate that the structural environment surrounding the dopant Eu3+ ion is distorted when compared to a bulk sample with a micrometer particle size. From the resulting emission spectra, the Ω2 and Ω4 Judd-Ofelt intensity parameters were calculated. The lifetimes of the 5D0 excited state for both the C2 and C3i sites were found to be nearly double that found for a similarly doped sample with larger particle size (bulk sample). This behavior is attributed to a change in the refractive index of the nanocrystalline material that in turn modifies the oscillator strength of the 4f ↔ 4f transitions.

Variation of Fluorescence Lifetimes and Judd-Ofelt Parameters between Eu3+ Doped Bulk and Nanocrystalline Cubic Lu2O3

We report a new scintillator based on a transparent ceramic of Lu 2 O 3 :Eu. The material has an extremely high density of 9.4 g/cm 3 , a light output comparable to CsI:Tl, and a narrow band emission at 610 nm that falls close to the maximum of the response curve of CCDs. Pixelation of the scintillator to prevent lateral spread of light enhances the spatial and contrast resolution, providing imaging performance that equals or surpasses all other currently known scintillators. Upon further development of readout technologies to take full advantage of its transparency, the new scintillator should play a major role in digital radiographic systems.

A new lutetia-based ceramic scintillator for X-ray imaging

Transparent ceramics have various potential applications such as infrared (IR) windows/domes, lamp envelopes, opto-electric components/devices, composite armors, and screens for smartphones and they can be used as host materials for solid-state lasers. Transparent ceramics were initially developed to replace single crystals because of their simple processing route, variability in composition, high yield productivity, and shape control, among other factors. Optical transparency is one of the most important properties of transparent ceramics. In order to achieve transparency, ceramics must have highly symmetric crystal structures; therefore, the majority of the transparent ceramics have cubic structures, while tetragonal and hexagonal structures have also been reported in the open literature. Moreover, the optical transparency of ceramics is determined by their purity and density; the production of high-purity ceramics requires high-purity starting materials, and the production of high-density ceramics requires sophisticated sintering techniques and optimized sintering aids. Furthermore, specific mechanical properties are required for some applications, such as window materials and composite armor. This review aims to summarize recent progress in the fabrication and application of various transparent ceramics.

Materials development and potential applications of transparent ceramics: A review

We report on the development of a new, large area, powdered scintillator screen based on Lu 2 O 3 (Eu) As reported earlier, the transparent ceramic form of this material has a very high density of 94 g/cm 3 , a high light output comparable to that of CsI(Tl), and emits in a narrow spectral band centered at about 610 nm Research into fabrication of this ceramic scintillator in a large area format is currently underway, however the process is not yet practical for large scale production Here we have explored fabrication of large area screens using precursor powders from which the ceramics are fabricated To date we have produced up to 16 × 16 cm 2 area screens with thickness in the range of 18 mg/cm 2  This paper outlines the screen fabrication technique and presents its imaging performance in comparison with a commercial Gd 2 O 2 S:Tb (GOS) screen

A new large area scintillator screen for X-ray imaging

A steel roughing grade coated cemented carbide cutting tool comprises WC grains equal to or less than 70 w/o of the tool substrate, from about 5 to about 10 w/o of a cobalt bonding phase and the remainder being metal carbide grains selected from the group TiC, TaC, NbC, HfC and combinations thereof. The average WC grain size is from about 0.9 to about 1.3 microns and less than 10% of the WC grains have a size less than 0.5 microns. The coated cemented carbide tool is coated with an adherent refractory coating layer. The coated cemented carbide cutting tool can be used to machine steel at rough and heavy rough cutting conditions.

Coated cemented carbide tool for steel roughing applications and methods for machining

Although LSO is one of the most successful scintillator developments for medical diagnostics in the last two decades, good single crystals are not commercially available in any quantity. Consequently, we explored the feasibility of developing a ceramic version of the material, which requires a considerably lower temperature to consolidate the material to essentially crystalline density. Consolidation of the ceramic was achieved by hot pressing at temperatures up to 1700degC and pressure of 8000 psi. Hot pressing causes a loss of oxygen resulting in strong coloration of the ceramic, which had to be removed by heating (ldquobleachingrdquo) in air at approximately 1100degC. The resultant specimens were colorless and highly translucent, but the anisotropic nature of the crystal structure precluded the achievement of full transparency. The scintillation performance of the resulting ceramics was characterized and compared with that of high light-output LSO single crystals. The scintillation efficiency as measured by energy spectra generally fell in the range of 50-60% of that of the crystals. While this would be adequate for PET applications, the limited transparency provides a barrier to such use. An alternative application would be in signal integrating techniques, such as CT, where it could provide an alternative to GOS but with higher speed. Here, the problem of afterglow assumes major importance. The afterglow is a function of many factors, including conditions of excitation. Further work on improving the LSO ceramics is considered.

A Ceramic Version of the LSO Scintillator

The authors report a new scintillator based on a transparent ceramic of Lu/sub 2/O/sub 3/:Eu. The material has an extremely high density of 9.4 g/cm/sup 3/ and a light output comparable to CsI:Tl. Its narrow-band emission at 610 nm perfectly matches the spectral response of charge coupled devices (CCDs). To enhance the spatial and contrast resolution, the authors have developed a special process to pixelate the scintillator and prevent the spread of light within the scintillator volume. The imaging performance of this pixelated device was evaluated using a thermoelectrically cooled CCD camera. The new scintillator is expected to play a major role in digital radiographic systems when readout technologies capable of taking advantage of the transparency are developed further.

Helmut Lingertat

Papers

A new lutetia-based ceramic scintillator for X-ray imaging

A new large area scintillator screen for X-ray imaging

Coated cemented carbide tool for steel roughing applications and methods for machining

A Ceramic Version of the LSO Scintillator

A new X-ray scintillator for digital radiography