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Boston, MA, United States

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 75.00K | Year: 1996

40094 November 8, 1996 ALEM Associates Of all the applications in which scintillators are used, none puts more rigorous demands on the material than high energy physics. The high radiation fluxes characteristic of these experiments requires both extremely short decay times (to enable high timing resolution) and minimal contribution from long decay components (to prevent count pile-up). Barium fluoride is the most effective inorganic scintillator for such applications, largely because of the unusually rapid decay (0.6 ns) of its fast component. Unfortunately, it has two major deficiencies: a long-lived slow component, which comprises over 85% of the total emission, and a particular sensitivity to damage by the very radiation it is measuring. This project explores a new approach to achieving improved ultrafast scintillators for high-energy radiation detection. A significant quantity (approximately 15 mole percent) of optically inert rare earth trifluorides are substituted into the basic alkaline earth difluoride lattice, and the host is doped with small amounts of other rare earths capable of d-f emission. Most of the energy that now goes to the undesirable long component should be diverted into a much more rapid emission in the 1-10 ns range, enhancing both timing resolution and radiation hardness without reducing the contribution from the fast component itself. The validity of the approach will be confirmed through spectroscopic and kinetic measurements on specially grown specimens, and the expected performance improvement will be assessed. Anticipated Results/Potential Commercial Applications as described by the awardee: The project will develop a scintillator material whose performance exceeds that of BaF2 in all three critical ways: enhanced timing resolution, reduced background, and greater radiation hardness. This will not only provide nuclear physicists with a superior measurement tool, but lead the way to improved materials for medical and industrial uses as well.

Roy S.,Boston University | Lingertat H.,ALEM Associates | Brecher C.,ALEM Associates | Sarin V.,Boston University
Optical Materials | Year: 2013

Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 nm and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 μm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 μm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 μm to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost three orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission. © 2012 Elsevier B.V. All rights reserved.

Wang Y.,Radiation Monitoring Devices, Inc. | Baldoni G.,Radiation Monitoring Devices, Inc. | Rhodes W.H.,ALEM Associates | Brecher C.,ALEM Associates | And 5 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Lanthanide gallium/aluminum-based garnets have a great potential as host structures for scintillation materials for medical imaging. Particularly attractive features are their high density, chemical radiation stability and more importantly, their cubic structure and isotropic optical properties, which allow them to be fabricated into fully transparent, highperformance polycrystalline optical ceramics. Lutetium/gadolinium aluminum/gallium garnets (described by formulas ((Gd,Lu)3(Al,Ga)5O12:Ce, Gd3(Al,Ga)5O12:Ce and Lu3Al 5O12:Pr)) feature high effective atomic number and good scintillation properties, which make them particularly attractive for Positron Emission Tomography (PET) and other γ- ray detection applications. The ceramic processing route offers an attractive alternative to single crystal growth for obtaining scintillator materials at relatively low temperatures and at a reasonable cost, with flexibility in dimension control as well as activator concentration adjustment. In this study, optically transparent polycrystalline ceramics mentioned above were prepared by the sintering-HIP approach, employing nano-sized starting powders. The properties and microstructures of the ceramics were controlled by varying the processing parameters during consolidation. Single-phase, high-density, transparent specimens were obtained after sintering followed by a pressure-assisted densification process, i.e. hot-isostatic- pressing. The transparent ceramics displayed high contact and distance transparency as well as high light yield as high as 60,000-65,000 ph/MeV under gamma-ray excitation, which is about 2 times that of a LSO:Ce single crystal. The excellent scintillation and optical properties make these materials promising candidates for medical imaging and γ-ray detection applications. © 2012 SPIE.

Rhodes W.H.,ALEM Associates | Wang Y.,Radiation Monitoring Devices, Inc. | Brecher C.,ALEM Associates | Gary Baldoni J.,Radiation Monitoring Devices, Inc.
Journal of the American Ceramic Society | Year: 2011

Pr-doped Lu 3Al 5O 12 (LuAG) transparent ceramic, a potential scintillator material, was fabricated by sinter/hot isostatic pressing (HIP). The specimens were subjected to various post-densification heat treatments and the evolution of porosity and its relationship to transparency was monitored and studied. Annealing was necessary to remove discoloration and to restore stoichiometry, but when performed at too high a temperature it caused a severe decrease in transparency. Transparency was restored by reHIPing, indicating that some nanometer-size pores remained even after the original HIP cycle, which expanded in size during annealing and contracted again during re-HIPing. Annealing at a lower temperature restored stoichiometry without serious transparency degradation, due to a favorable difference in diffusion rates for mass transfer and O 2- diffusion. This phenomenon illustrates a fundamental difference between residual porosity in ceramics consolidated by pressureless and pressure-assisted processes. © 2011 The American Ceramic Society.

Roy S.,Boston University | Lingertat H.,ALEM Associates | Brecher C.,ALEM Associates | Sarin V.K.,Boston University
IEEE Transactions on Nuclear Science | Year: 2012

While polycrystalline ceramic of Ce +3 doped lutetium oxyorthosilicate (LSO) has demonstrated scintillation characteristics equivalent to those of single crystal material, it lacks in optical quality. It is projected that if their grain size could be reduced to the nanometer range they would be smaller than the wavelength of light thereby minimizing scattering and substantially improving optical quality. In this investigation ceramic LSO:Ce that is much more transparent than would be expected from a highly anisotropic material, has been successfully produced by hot pressing at 75 MPa in a graphite die and furnace. The conditions necessary for powder processing and densification were optimized so as to produce dense LSO:Ce ceramic discs with an average grain size of 700 nm. Appreciable improvement in optical properties was observed, with decay and emission levels comparable with LSO single crystals, the light output was some 20% below that of single crystal. The degradation of light output in the nanoceramic is attributed to the formation of quenching centers associated with the loss of oxygen during densification, to which such nanomaterials are highly susceptible. © 2012 IEEE.

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