Search

The scintillation properties and time-resolved spectroscopy results for Li3 Lu(PO4)2 :Ce-a new Ce3+-activated crystalline scintillator have been determined. This material contains stoichiometric amounts of Li, and can be synthesized either with the use of 6Li-enriched or 6Li-depleted isotopes, for achieving thermal neutron sensitivity or x-ray/gamma-ray detection without neutron sensitivity, respectively. The scintillation of Li3Lu(PO4)2:Ce is based on the Ce3+-activator UV (336 and 360 nm) emission, and for a 2 wt. % activation level and gamma ray photon excitation, it exhibits a light yield of about 5300 photons/MeV and a decay time constant of 24.7 ns-with no longer component observed in the time range up to 2 μs. Host emissions, while present for some specific excitations in the region of the bandgap energy, do not appear to play a significant role in the material's scintillation that is most probably accomplished by the consecutive capture and recombination of free band holes and electrons on the activator ions. [ABSTRACT FROM AUTHOR]

ZnO-based scintillators are particularly well suited for use as the associated particle detector in a deuterium-tritium (D-T) neutron generator. Application requirements include the exclusion of organic materials, outstanding timing resolution, and high radiation resistance. ZnO, ZnO:Ga, ZnO:In, ZnO:In,Li, and ZnO:Er,Li have demonstrated fast (sub-nanosecond) decay times with relatively low light yields. ZnO:Ga has been used in a powder form as the associated particle detector for a D-T neutron generator. Unfortunately, detectors using powders are difficult to assemble and the light yield from powders is less than satisfactory. Single-crystal ZnO of sufficient size has only recently become available. New applications for D-T neutron generators require better timing resolution and higher count rates than are currently available with associated particle detectors using YAP:Ce as the scintillator. Recent work suggests that ZnO-based scintillators can provide alpha-particle-excited light yields comparable to YAP:Ce scintillators. ZnO-based polycrystalline ceramic scintillators offer the advantages of high light yield, ease of fabrication, low cost, and robust mechanical properties. Precursor powders used in these studies include ZnO and ZnO:Ga powders synthesized using solution-phase, urea precipitation, and combustion synthesis techniques as well as ZnO powder from a commercial vendor. Precursor powders have been sintered using uniaxial hot, pressing and spark plasma sintering techniques. Photoluminescence measurements have confirmed that, for most samples, the emissions from these sintered bodies consist primarily of slow, visible emissions rather than the desired sub-nanosecond near-band-edge emissions. Subsequent hydrogen treatments have shown significant improvements in the luminescence characteristics of some ceramic bodies, while other samples have shown no change in luminescence. [ABSTRACT FROM AUTHOR]

We report the discovery of a new family of Ce[sup3+] -activated phosphate glass scintillators that can be formed either with or without the addition of [sup6]Li, for neutron or X-ray/gamma-ray radiation detection, respectively. Trivalent cerium can be efficiently introduced into these phosphate glasses in surprisingly high concentrations in the form of anhydrous cerium tri-chloride. Additionally, these glasses can be melted and poured at the relatively low temperatures of 1000-1050°C (i.e., substantially lower than silicate glasses), and to retain the cerium in the trivalent state it is not necessary to maintain highly reducing conditions during the synthesis process. The family of alkaline-earth-alkali phosphate glasses investigated here represents a system with two dissimilar cations-thereby offering a large range of potential compositional variations, substitutions, and combinations. In order to alter the scintillator characteristics, we have explored part of that compositional space by studying Ca-Na, Ca-Li, Ca-Cs, Ca-Rb, Ca-K and Ca-Ba-Na phosphate glasses, as well as various co-doping and post-synthesis thermal processing schemes. A series of experiments under x ray, gamma ray, and neutron excitations was carried out. The broad, peaking at about 354 nm, UV scintillation of these glasses is well suited for applications that use common photomultipliers with bi-alkali photo-cathodes. Pulse shape measurements show that the primary component of the scintillation in most of these glasses corresponds to 75-90% of the emitted photons, and it decays with a time constant of 30 to 40 ns, which classifies these materials as reasonably fast scintillators. Although the gamma-induced light yield of these new scintillating phosphate glasses is, thus far, only about 30% of that of commercial GS20 silicate glass, due to the generally faster scintillation, the initial amplitude of the scintillation pulse of these glasses is close to that of the above-mentioned GS20 scintillator. [ABSTRACT FROM AUTHOR]

For several decades most of the efforts to develop new scintillator materials have concentrated on high-light-yield inorganic single-crystals while polycrystalline ceramic scintillators, since their inception in the early 1980's, have received relatively little attention. Nevertheless, transparent ceramics offer a promising approach to the fabrication of relatively inexpensive scintillators via a simple mechanical compaction and annealing process that eliminates single-crystal growth. Until recently, commonly accepted concepts restricted the polycrystalline ceramic approach to materials exhibiting a cubic crystal structure. Here, we report our results on the development of two novel ceramic scintillators based on the non-cubic crystalline materials: Lu2 SiO5:Ce (LSO:Ce) and LaBr3:Ce. While no evidence for texturing has been found in their ceramic microstructures, our LSO:Ce ceramics exhibit a surprisingly high level of transparency/translucency and very good scintillation characteristics. The LSO:Ce ceramic scintillation reaches a light yield level of about 86% of that of a good LSO:Ce single crystal, and its decay time is even faster than in single crystals. Research on LaBr3:Ce shows that translucent ceramics of the high-light-yield rare-earth halides can also be synthesized. Our LaBr3:Ce ceramics have light yields above 42 000 photons/MeV (i.e., >70% of the single-crystal light yield). [ABSTRACT FROM AUTHOR]

As part of an ongoing investigation of the scintillation properties of zinc-oxide-(ZnO)-based scintillators, several melt-grown, ZnO single crystals have been characterized using alpha-particle excitation, infrared reflectance, and room temperature photoluminescence. The crystals, grown by Cermet, Inc., using an oxygen-pressurized melt-growth process, were doped with Group 1 elements (Li), Group 2 elements (Mg), Group 3 elements (Ga, In) and Lanthanides (Gd, Er, Tm). The goals of these studies are to better understand the scintillation mechanisms associated with various members of the ZnO scintillator family and to then use this knowledge to improve the radiation detection capabilities of ZnO-based scintillators. One application for which ZnO is particularly well suited as a scintillator is as the associated particle detector in a deuterium-tritium (D-T) neutron generator. Application requirements include the exclusion of organic mate- rials, outstanding timing resolution, and high radiation resistance. ZnO:Ga and ZnO:In have demonstrated fast (subnanosecond) decay times with relatively low light yields, and ZnO(Ga) has been used in a powder form as the associated particle detector for a D-T neutron generator. Four promising candidate materials, ZnO, ZnO:Ga, ZnO:In,Li, and ZnO:Er,Li, were identified in this study. These four samples demonstrated sub-nanosecond decay times and alpha-particle-excited-luminescence comparable to BC-400 fast plastic scintillator. The ZnO:Mg,Ga, ZnO:Gd, and ZnO:Li samples demonstrated appreciable slow (microsecond) decay components that would be incompatible with high-counting-rate applications. [ABSTRACT FROM AUTHOR]