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Now showing items 1 - 16 of 70

  • Ionic Conductivity of TlBr 1-xI x (x = 0, 0.2, 1): Candidate Gamma Ray Detector

    Bishop, S.R.   Ciampi, G.   Lee, C.D.   Kuhn, M.   Tuller, H.L.   Higgins, W.   Shah, K.S.  

    The ionic conductivity of TlBr, TlI and their solid solutions, candidates for high energy radiation detection, was examined using impedance spectroscopy. The orthorhombic to cubic phase change in TlI was observed via a steep change in conductivity with increasing temperature, whereas the TlBr-TlI solid solution was cubic throughout the measured temperature range, in agreement with the literature. The intrinsic conductivity of the cubic phase of each material showed nearly identical behavior, indicating that I substitution for Br has little to no effect on the combined defect formation and transport parameters in the studied range. Additionally, optical transmission was correlated with I concentration.
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  • Doping impact on the electro-optical properties of a TlBr crystal

    Dmitriev, Y.   Bennett, P.R.   Cirignano, L.J.   Gupta, T.K.   Higgins, W.M.   Shah, K.S.   Wong, P.  

    TlBr doped with In and Pb was synthesized and grown using a vertical Bridgman method. The segregation coefficients of both dopants in TlBr were calculated using the different experimental optical and electrical characteristics of (TlBr) 0.973-(InBr) 0.027 and (TlBr) 0.972-(PbBr 2) 0.078 crystals. The solubility of In and Pb in the liquid phase is higher than their solubility in solid TlBr: k s(In)=1.06 and k s(Pb)=1.3-1.6. Doping with both impurities leads to degradation of the electrical, optical, and detector properties of TlBr. [All rights reserved Elsevier].
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  • Effects of Ce concentration on scintillation properties of LaBr 3:Ce

    Glodo, J.   Moses, W.W.   Higgins, W.M.   van Loef, E.V.D.   Wong, P.   Derenzo, S.E.   Weber, M.J.   Shah, K.S.  

    In this communication, we investigate the scintillation properties of LaBr 3:Ce as a function of Ce concentration. We have studied crystals nominally doped with 0.5%, 5%, 10%, 20%, and 30%Ce (by mole). Previous reports suggest that as the Ce content increases, there is a decrease in light output and little or no change in decay time constants. These results show that the light output does not change with Ce concentration up to 30% and depends mostly on the crystal quality. On the other hand we have found the timing properties to be a strong function of Ce concentration. As the Ce content increases, the principal decay time constant of scintillation decreases from ~26 ns for 0.5%Ce to ~17 ns for crystals with >5% Ce. Moreover, there is a significant change in rise time constants. The rise time measured for a sample doped with 0.5%Ce is up to 9 ns, whereas for samples doped with >10% Ce it is less than 0.5 ns. The change of rise time has a major effect on the timing properties of this scintillator, with timing resolution improving from 361 ps to less than 100 ps (full width at half maximum)
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  • CeBr/sub 3/ scintillators for gamma-ray spectroscopy

    Shah, K.S.   Glodo, J.   Higgins, W.   van Loef, E.V.D.   Moses, W.W.   Derenzo, S.E.   Weber, M.J.  

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  • High energy resolution scintillation spectrometers

    Shah, K.S.   Glodo, J.   Klugerman, M.   Higgins, W.M.   Gupta, T.   Wong, P.  

    In this paper, we report on cerium doped scintillator-LaBr 3 : Ce for gamma ray spectroscopy. Crystals of this scintillator have been grown using the Bridgman process. This material when doped with cerium has high light output (>60 000 photons/MeV) and fast principal decay constant (<30 ns). The peak of LaBr 3 : Ce emission is at 360 nm. LaBr 3 : Ce shows excellent energy resolution for gamma ray detection. For 662 keV gamma rays ( 137 Cs source), energy resolution of 2.6% (full-width at half-maximum) has been recorded at room temperature for LaBr 3 : Ce crystals coupled to a photomultiplier. This energy resolution is over two times better than that of NaI(Tl) scintillators. Analysis of the energy resolution of LaBr 3 : Ce scintillators is presented. Energy resolution of LaBr 3 : Ce crystals coupled to silicon avalanche photodiodes is also discussed
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  • Position Sensitive APDs for Small Animal PET Imaging

    Shah, K.S.   Grazioso, R.   Farrell, R.   Glodo, J.   McClish, M.   Entine, G.   Dokhale, P.   Cherry, S.R.  

    In this paper, investigation of position sensitive avalanche photodiodes (PSAPDs) as optical detectors for reading out segmented scintillation arrays of LSO in high resolution PET modules is reported. PSAPDs with 8times8 mm 2 and 14times14 mm 2 area have been characterized with single LSO crystals and arrays. Energy resolution of 19% (FWHM) for 511 keV gamma-rays and coincidence timing resolution of ~3 ns (FWHM) have been recorded with PSAPD coupled to 1times1times20 mm 3 LSO detectors. Flood histogram studies have been successfully conducted by coupling multi-element element LSO arrays (1 mm pixels, 20 mm tall) to the PSAPDs. Finally, depth of interaction (DOI) resolution of <4.5 mm (FWHM) has been measured by coupling two PSAPDs on opposite ends of a 20 mm long LSO crystal with a 1times1 mm 2 cross section. Based on these results, PSAPDs appear to be promising for high resolution PET. An important advantage of these PSAPDs is significant reduction in electronic readout requirements
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  • LuI/sub 3/:Ce-a new scintillator for gamma ray spectroscopy

    Shah, K.S.   Glodo, J.   Klugerman, M.   Higgins, W.   Gupta, T.   Wong, P.   Moses, W.W.   Derenzo, S.E.   Weber, M.J.   Dorenbos, P.  

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  • LaCl3:Ce scintillator for γ-ray detection

    Shah, K.S.   Glodo, J.   Klugerman, M.   Cirignano, L.   Moses, W.W.   Derenzo, S.E.   Weber, M.J.  

    In this paper, we report on a relatively new cerium-doped scintillator—LaCl3 for γ-ray spectroscopy. Crystals of this scintillator have been grown using Bridgman method. This material when doped with 10%cerium has high light output (50,000 photons/MeV) and fast principal decay time constant (20ns). Furthermore, it shows excellent energy resolution for γ-ray detection. For example, energy resolution as low as 3.2%(FWHM) has been achieved with 662keV photons (137Cs source) at room temperature. Also, high timing resolution (264ps—FWHM) has been recorded with LaCl3-PMT and BaF2-PMT detectors operating in coincidence using 511keV positron annihilation γ-ray pairs. Details of crystal growth, scintillation properties, and variation of these properties with cerium concentration are also reported.
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  • LaBr/sub 3/:Ce scintillators for gamma-ray spectroscopy

    Shah, K.S.   Glodo, J.   Klugerman, M.   Moses, W.W.   Derenzo, S.E.   Weber, M.J.  

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  • High-resolution pixel detectors for second generation digital mammography

    Tumer, T.O.   Shi Yin   Cajipe, V.   Flores, H.   Mainprize, J.   Mawdsley, G.   Rowlands, J.A.   Yaffe, M.J.   Gordon, E.E.   Hamilton, W.J.   Rhiger, D.   Kasap, S.O.   Sellin, P.   Shah, K.S.  

    Hybrid CdZnTe, CdTe, GaAs selenium and PbI 2 pixel detector arrays with 50 times 50 mum 2 pixel sizes that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. These detectors have superior X-ray quantum efficiency compared to either emulsion-based film, phosphor-based detectors or other low-Z solid-state detectors such as silicon. During this work, CdZnTe and CdTe pixel detectors gave the best results. The other detectors are at very early stages of development and need significant improvement. Among other detectors, selenium is showing the highest potential. The preliminary results show that single crystal CdZnTe detectors yield better results in Detective Quantum Efficiency (DQE) as well as in images obtained from phantoms, compared to the polycrystalline CdZnTe detectors. This is due to the non-uniformities in the polycrystalline CdZnTe that degrade the charge transport properties. In this paper, preliminary results from thin (0.15 to 0.2 mm) CdZnTe and CdTe detectors will be presented in terms of MTF, DQE and phantom images. Because of the charge-coupling limitation of the readout Application Specific Integrated Circuit (ASlC) that was originally designed for Si detectors, the detector is biased to collect holes from the input. This charge collection mode limits the CdZnTe detector performance. Their DQE measurements yield 25% and 65% for the polycrystal and single-crystal CdZnTe detectors, respectively. Polycrystal CdTe test detectors were also hybridized to the same type charge readout chip. Since CdTe has much longer hole-propagation lengths compared to CdZnTe, it shows better performance in the hole-collecting mode. However, it suffers from polarization. Excellent images were also obtained from the CdTe detectors. Future work to redesign the readout ASlC and thus improve the detector performance will be discussed. These detectors can also be used for other medical radiography with increased thickness and also for industrial imaging such as non-destructive evaluation and non-destructive inspection
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  • Position-sensitive avalanche photodiodes for gamma-ray imaging

    Shah, K.S.   Farrell, R.   Grazioso, R.   Harmon, E.S.   Karplus, E.  

    In this paper, we report on the investigation of silicon avalanche photodiodes (APDs) for high-energy photon imaging applications. This includes a new APD design that provides X-ray and gamma-ray imaging with significant reduction in electronic readout requirements. This new APD design, referred to as position-sensitive avalanche photodiode (PSAPD), involves charge sharing amongst the electrodes that enable determination of position of interaction. PSAPDs with 14 times 14 mm 2 area have been fabricated using planar processing. The performance of these devices has been evaluated for energy resolution, timing resolution (4 ns full-width at half-maximum), and spatial resolution (~300 mum intrinsic spatial resolution). The potential of these APDs in high-energy physics and medical imaging is addressed
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  • X-ray imaging with PbI2-based A-Si:H flat panel detectors

    Shah, K.S.   Street, R.A.   Dmitriyev, Y.   Bennett, P.   Cirignano, L.   Klugerman, M.   Squillante, M.R.   et. al.  

    In this paper, we discuss a new X-ray imaging detector which consists of lead iodide polycrystalline films as sensor and amorphous silicon flat panel arrays as read out. We present our investigation of such a detector in 5cm x 5cm format with 100μm pixels. The signal amplitude, and sensitivity of the films have been measured along with spatial resolution properties such as line spread function (LSF) and modulation transfer function (MTF). Real-time imaging performance at 30frames/s of lead iodide films has also been evaluated using vidicon tube approach. Important properties of lead iodide film are also discussed. Finally, the potential applications of this detector are analyzed.
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  • Dual APD array readout of LSO crystals: optimization of crystal surface treatment

    Shao, Y.   Meadors, K.   Silverman, R.W.   Farrell, R.   Cirignano, L.   Grazioso, R.   Shah, K.S.   Cherry, S.R.  

    We are developing a compact positron emission tomography (PET) detector module with a depth of interaction capability (DOI) based on a lutetium oxyorthosilicate (LSO) scintillator array coupled at both ends by avalanche photodiode (APD) arrays. This leads to a detector with high sensitivity that can provide high and uniform image resolution. We report studies on improving the DOI resolution by optimizing the crystal surface treatment. Six 2times2times20 mm LSO crystals were treated with different surface finishes along their length: raw saw-cut, polished optical finish, and chemically etched by hot anhydrous phosphoric acid (H 3PO 4) with etching times varying from 1 to 5 min. The ratio of the signals from the two APD arrays was used to measure DOI, and the sum of the signals to measure the total light output. Crystals finished by chemical etching for 2-3 min gave the best overall detector performance, with DOI resolutions ranging from 3.1 to 3.9 mm for events above a 150-keV threshold and uniform light output for different DOI positions. The energy resolution ranged between 14% and 18%. This detector design appears promising for PET applications requiring very high resolution and high sensitivity, for example, in small animal imaging and human breast imaging
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  • RbGd/sub 2/Br/sub 7/:Ce scintillators for gamma-ray and thermal neutron detection

    Shah, K.S.   Cirignano, L.   Grazioso, R.   Klugerman, M.   Bennett, P.R.   Gupta, T.K.   Moses, W.W.   Weber, M.J.   Derenzo, S.E.  

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  • Pixellated CdZnTe detector for emission/transmission computed tomography

    Cirignano, L.   Shah, K.S.   Bennett, P.R.   Klugerman, M.   Dmitryev, Y.   Squillante, M.R.   Narita, T.   Bloser, P.   Grindlay, J.   Hasegawa, B.H.   Iwata, K.  

    A small pixellated CdZnTe array is tested for suitability in a prototype SPECT system designed to acquire both emission and transmission data. Determining the optimum contact design and obtaining performance estimates of single photon acquisition are the primary focus. Flood field and collimated 57Co sources irradiated the 16 pixel array (5 mm thick and 1.5 mm pixels) to determine photopeak efficiencies and detector response with different event collection techniques. Intrinsic full energy peak efficiency averaged 72% for an 18 keV acceptance window. A small irradiation spot scanned an array region, revealing detector response from nearby pixels. Post processing spectra compare coincident and anti-coincident acquisition. Additionally, current mode tests compare linearity with a CdWO 4/Si p-i-n detector
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  • Lead iodide optical detectors for gamma ray spectroscopy

    Shah, K.S.   Bennett, P.   Klugerman, M.   Moy, L.   Cirignano, L.   Dmitriyev, Y.   Squillante, M.R.   Olschner, F.   Moses, W.W.  

    This paper describes the research performed in developing low noise, high quantum efficiency lead iodide photodetectors for use with scintillators. These photodetectors operate with very low leakage current and show high quantum efficiency (>60%) in 350 to 500 nm region. Successful scintillation studies have been performed at room temperature as well as elevated temperatures (100degC) using PbI 2 photodetectors with LSO and CsI(Na) scintillators. Detailed analysis of noise has also been performed and potential applications are discussed
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