Excellent Scintillation Research Articles

Scintillation properties of CsBa2Br5:Eu2+

Abstract In this study, the scintillation properties of Eu 2+ activated CsBa 2 Br 5 are reported. It is an analog of Eu 2+ doped CsBa 2 I 5 scintillator that exhibits excellent scintillation properties. Microcrystalline powder samples of this compound were synthesized by reaction in the molten state of cesium bromide, barium bromide and europium bromide. The concentration of an Eu was varied from 0% to 10%. The luminescence was studied under UV and X-ray excitation. The light output is strongly Eu 2+ concentration dependent, reaching an estimated maximum of about 92,000 photons/MeV at 2% Eu under X-ray excitation. About 50% of the scintillation light decays in less than 1 μs. CsBa 2 Br 5 :Eu 2+ exhibits a complex concentration dependent emission centered around 435 nm.

Combinatorial Optimization of (YxLu1−x−y)3Al5O12:Ce3y Green-Yellow Phosphors

A combinatorial chemistry method was used to synthesize and screen (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) green-yellow phosphors. The material libraries were obtained using an inkjet delivery system and screened for their fluorescence under an ultraviolet light of 365 nm. The optimized composition was identified to be (Y(0.2)Lu(0.788))(3)Al(5)O(12):Ce(3+)(0.036). Scale-up experiments confirmed that the optimized composition of the phosphor showed the highest luminescence intensity and an excellent scintillation performance with a short decay time (<60 ns). The results indicated that the (Y(x)Lu(1-x-y))(3)Al(5)O(12):Ce(3y) could be potentially useful as green-yellow phosphors for ceramic scintillators.

BaBrI:Eu 2+, a new bright scintillator

The scintillation properties of BaBrI:Eu 2+ are reported. Crystals were produced by the vertical Bridgman technique in a sealed quartz ampoule. Excellent scintillation properties were measured. A light yield of 81,000±3000 photons per MeV (ph/MeV) of absorbed gamma-ray energy was measured. An energy resolution (FWHM over peak position) of 4.8±0.5% was observed for the 662 keV full absorption peak. Pulsed X-ray luminescence measurements show two exponential decay components of 297 and 482 ns with a contribution to the total light output of 23% and 77%, respectively. Under X-ray and UV excitation, the emission corresponds to a broadband center at 413 nm. These initial values make BaBrI:Eu 2+ one of the brightest and the fastest known Eu 2+-doped scintillators.

Eu 2+-doped Ba 2CsI 5, a new high-performance scintillator

The crystal growth and scintillation properties of Ba 2CsI 5:Eu 2+ are reported. Crystals were produced by the vertical Bridgman technique in a sealed quartz ampoule. Ba 2CsI 5:Eu 2+ presents excellent scintillation properties. An estimated light yield of 97,000±5,000 photons per MeV (ph/MeV) of absorbed gamma-ray energy was measured. An energy resolution (FWHM over peak position) of 3.8±0.3% was observed for the 662 keV full absorption peak. Pulsed X-ray luminescence measurements show a relatively complex time response with four exponential decay components of 48,383, 1500 and 9900 ns with a contribution to the total light output of 1%, 26%, 68% and 25%, respectively. Under X-ray and UV excitation, the emission corresponds to a broadband centered at 2.85 eV. First principles calculations show strong localization of the excited state on the Eu site. Ba 2CsI 5:Eu 2+ has a density of about 5 g/cm 3. These first reported scintillation properties make Ba 2CsI 5:Eu 2+ a very high-performance scintillator.

${\rm Lu}_{2}{\rm SiO}_{5}:{\rm Ce}$ Optical Ceramic Scintillator for PET

Phase-pure transparent LSO ceramic was obtained, with its scintillation properties rivaling those of single crystalline LSO. The transparent LSO ceramic was prepared by a nano-technology approach. The densities of the LSO ceramic increased with increasing sintering temperature. Further SEM examination confirmed the decrease of the porosity during densification of the ceramic. Pores were segregated at grain boundaries after sintering. Hot isostatic pressing (HIPing) was employed to further densify the ceramic and eliminate porosity after sintering. Transparent polycrystalline LSO ceramics were obtained after the final HIP. XRD examination confirms single monoclinic LSO phase. A light output as high as 30,100 ph/MeV was obtained using a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> Na excitation source. LSO ceramic showed an energy resolution of 15% (FWHM) at 662 keV ( <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs source) and a fast scintillation decay of 40 ns due to the 5d \ura 4f transition of Ce <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> . The excellent scintillation and optical properties make LSO ceramic a promising candidate for future gamma-ray spectroscopy as well as medical imaging applications.

Optical physics of scintillation imagers by GEANT4 simulations

The recent developments of LaBr 3:Ce crystals makes their use in a system of gamma imaging for Single Photon Emission Tomography (SPET) applications very attractive, mainly due to their excellent scintillation properties. In this work we use the Monte Carlo simulations in order to model the optical behavior of three crystal configurations. Our goal is to better understand the intrinsic properties of a gamma camera based on LaBr 3:Ce crystals coupled to a position-sensitive photomultiplier tube. To this aim, the spatial and energy resolutions obtained from optimum photodetection conditions are investigated.

Underground argon for low background detectors

The excellent scintillation characteristics of argon, including a high light yield and strong discrimination between minimum and highly ionizing particles, make it a valuable material for use in a variety of detectors, most notably detectors or WIMP-induced nuclear recoils. However, the presence of the cosmogenically induced radioactive isotope 39Ar in atmospheric argon generates a background rate of ∼1 Bq/kg atmospheric argon. We have recently identified sources of argon in underground reservoirs with 39Ar content reduced by at least a factor of 20 (limit only) with respect to atmospheric argon. This brings multi-ton scale liquid argon detectors into the realm of possibility.

Extractive-scintillating resin produced by radiation polymerization

The characterization of a resin material is presented, which contains selective complexing and scintillating molecules in chemically bound form. The resin material is produced via radiation polymerization of the solution of 2-(4-allyloxy-phenyl)-5-phenyl oxazole, 5-(allyloxy-phenyl)-2-[4-(5-phenyl-oxazole-2-il)-phenyl] oxazole, diethylene glycol dimethacrylate (DEGMA), styrene and the allyl derivative of a 18C6 crown ether-dicarbolic acid complexing agent. The product is a macroporous polymer matrix, which shows both excellent scintillation properties and ion binding capacity for radioanalytical purposes.

Ba 3 B P 3 O 12 : Eu 2 + —A potential scintillation material

The sample of Eu2+-doped Ba3BP3O12 was prepared by a solid-state reaction at high temperature and was showed to be an excellent scintillator when excited with hard x ray s. The phosphor showed a broad emission band in the wavelength range of 400–650 nm and a comparable light yield with that of Bi4Ge3O12 powders. Its room temperature fluorescence decay curve exhibited a two-exponent shape with decay time of 20.0±1.4ns (98.97%) and 522±9ns (1.03%), respectively. Considering the suitable emission wavelength range, large light yield, short decay time, moderate density, moderately low melting point, and nonhygroscopic property of Ba3BP3O12:Eu2+, one has reason to assume that this compound might find an application as a new scintillation material.

A new radiation damage phenomenon of LSO:Ce scintillation crystal

Cerium-doped lutetium oxyorthosilicate (LSO:Ce) is an excellent scintillator with a large radiation hardness. But, in this work, some LSO:Ce crystals grown by SIC showed a new radiation damage phenomenon after exposure to 60Co γ-rays. An absorption band peaking at near 430 nm was observed. Because of the absorption the emission spectra were distorted but no new emission center appeared. There is no new thermoluminescence (TL) peak in the TL curve but the relative intensity of peaks is different from that of normal samples. The peaks at 490 and 546 K may be attributed to the appearance of absorption band that was proved by annealing at different temperatures. Absorption band can be eliminated a little at 200 °C and completely at 300 °C, either in air or in N 2 atmosphere.

Comparative study of CWO and ZnSe(Te) scintillation detector on the performance of X-ray imaging system

Recently, much attention has been paid to ZnSe(Te) semiconductor scintillator because of its excellent scintillation characteristics. Linear-array detector modules based on the conventional CdWO4 (CWO) and new ZnSe(Te) scintillator blocks were fabricated and tested for comparison for the purpose of applying them in X-ray inspection system. From the point of view of photocurrent and of detective quantum efficiency (DQE), ZnSe(Te) showed better performance in the low-energy X-ray system and was competitive to CWO in the high-energy X-ray system when the depth of scintillator is optimized to the energy in use. The site test of these modules in a prototype container inspection system using 340kVp X-ray showed equivalent image qualities.

Growth by Bridgman method and luminescence properties of Na:PbFCl crystal

Lead fluoride chloride crystal with doped sodium was grown by modified Bridgman method. Crystal growth and luminescence properties including transmittance, photoluminescence, X-ray excited luminescence and luminescence decay time are discussed. Photoluminescence measure shows that the luminescence intensity of crystal is improved by doped sodium. Only a fast luminescence component is detected. So Na:PbFCl crystal is a more excellent inorganic scintillator.

Growth by Bridgman method and luminescence properties of Na:PbFCl crystal

Lead fluoride chloride crystal with doped sodium was grown by modified Bridgman method. Crystal growth and luminescence properties including transmittance, photoluminescence, X-ray excited luminescence and luminescence decay time are discussed. Photoluminescence measure shows that the luminescence intensity of crystal is improved by doped sodium. Only a fast luminescence component is detected. So Na:PbFCl crystal is a more excellent inorganic scintillator.

Structured LiI scintillator for thermal neutron imaging

We are currently developing high-resolution high-efficiency microcolumnar LiI films for thermal neutron imaging. The films are produced by the vapor deposition of LiI on a fiber-optic substrate and hermetically sealed in a specially designed aluminum package. Our work has produced up to 1.2-mm-thick films with column diameters of approximately 30 /spl mu/m. We have also performed imaging studies by optically coupling some of these films to a fiber-optic taper-based charge-coupled device. The imaging performance of the system was experimentally evaluated at Radiation Monitoring Devices, Inc., as well as at the thermal neutron port of the University of Massachusetts Lowell Research Reactor. The LiI films exhibited excellent scintillation characteristics with a spatial resolution as high as 4.5 lp/min (line pairs per millimeter). This paper outlines the film characterization and performance evaluation conducted during the course of the study. The new sensor described here is expected to usher in the development of large-area high-resolution digital thermal neutron detectors with improved detection efficiency and dynamic range and faster readout times than the current sensors.

Comparison of the scintillation properties of LSO:Ce manufactured by different laboratories and of LGSO:Ce

We measured photoelectron yield, light output, decay times of the light pulses, cerium concentration, energy resolution and time resolution of LSO:Ce manufactured by different laboratories and LGSO:Ce. The LSO samples show excellent scintillation properties: high light output, close to 30,000 ph/MeV and good energy resolution of 7.3% FWHM for /sup 137/Cs /spl gamma/- source full energy peak. Time resolution measured in geometry fulfilling the PET scanners requirements is equal to 450 ps. We also present results from the measurements with LGSO:Ce by Hitachi Chemical Co., which is of similar chemical composition to LSO. LGSO, at present stage of development, shows about 20% lower light output than LSO and energy resolution of 12.4% FWHM for 662 KeV /spl gamma/-rays. LSO crystals used in our studies possess similar in scintillation properties, although we suppose that the details of the productions method are different due to the differences in Ce concentration. LGSO is a new and very promising scintillator due to lower background radiation in comparison to LSO, but it features worse energy resolution and smaller number of photoelectrons.

Theoretical explanation of the quenching of luminescence in cerium-doped ytterbium oxyorthosilicate

A remarkable result in applied solid-state physics is that whereas Ce-doped yttrium oxyorthosilicate, Y2(SiO4)O:Ce, is an excellent scintillator, the related Ce-doped ytterbium oxyorthosilicate, Yb2(SiO4)O:Ce, does not scintillate at all at room temperature. These compounds, Y and Yb, besides possessing the same crystal structure, both are trivalent and yield almost identical ionic radii. In order to understand the difference between the luminescent properties of these materials, we have performed an ab initio calculation to investigate the charge-transfer mechanism involving their first excited states. By using a representative cluster model, a crossing is found between the ground and the excited state of the ytterbium compound, though not so in the yttrium compound. This suggests that in the solid state, the luminiscence quenching can occur via a nonradiative transition, although luminescence at low temperature might thus be feasible. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 198–203, 2000

Surface polishing of GSO scintillator using chemical process

A Ce doped Gd/sub 2/SiO/sub 5/, (GSO) single crystal is an excellent scintillator featuring a large light output, a short decay constant and a high absorption coefficient. It was shown in our previous studies that the surfaces of the scintillator should be polished to get scintillation light output efficiently especially for long and narrow scintillators. Therefore, we newly developed a chemical process to polish the GSO crystal. The surface of the GSO crystal was found to become smooth when it was etched using anhydrous orthophosphoric acid at 150-300/spl deg/C. The process was also proved to be applicable to large size crystal such as 20/spl times/20/spl times/200 mm/sup 3/ preventing thermal shock crack. An improvement in the scintillator efficiency was confirmed using the chemical polishing process.

Scintillation characteristics of GSO single crystal grown under O/sub 2/-containing atmosphere

A Ce doped Gd/sub 2/SiO/sub 5/ (GSO) single crystal is an excellent scintillator featuring a large light output, a short decay constant and a high absorption coefficient. We have investigated dependence of the scintillation characteristics on the growth atmosphere. GSO crystal is usually grown in pure N/sub 2/, which due to thermal etching during the growth always roughens the boule surface, inducing some micro-cracks on the surface which often triggers the large crack in the boule. To eliminate this, we first introduced 1 vol% O/sub 2/-containing N/sub 2/ gas for the growth atmosphere. The resultant boule turned to be very smooth in surface, but pale yellow in color and degraded in the scintillation characteristics. To retain these properties, we then introduced an annealing process and found the annealing under pure N/sub 2/ atmosphere quite effective on the recovery both in color and scintillation properties. >

Low temperature test of photomultiplier tubes

The liquid rare gases have excellent scintillation properties and there are increasingly good prospects for their use in radiation detectors having a wide range of applications in different fields, such as medical radionuclide imaging (Chepel, 1993; Chepel et al., 1994), high and medium energy particle physics (Akimov et al.,1993), astrophysics (Aprile et al.,1989). Despite the new photosensitive devices that have been developed in recent years, photomultipliers are still the photodetectors most widely used for the detection of the liquid rare gases scintillation light. To increase the efficiency of light detection it is very often mandatory to place the photomultiplier very near, or even inside, the detector, which means operating the PM at low temperature (the boiling point of xenon and krypton is -108C and -153C respectively). The manufacturers usually give -30°C as the lowest working temperature and very little information on the behaviour of photomultipliers at lower temperatures is available in literature (Ichige et al.,1993). Thus, it is necessary to study the performance of photomultipliers in the range of 7r: temperatures of interest in view of the liquid rare gases detectors.

Prospects for a solar neutrino detector with LiI(Eu)

We have demonstrated that LiI(Eu) is an excellent scintillation crystal for measuring electromagnetic radiation. It has a low detection threshold with decent energy resolution. Its favourable chemical-physical properties and nuclear structure make it a unique and desirable medium for solar neutrino detection. The prospects for a solar neutrino detector using LiI(Eu) scintillation crystals is examined.