Scintillators play an important role in radiation detection and imaging. Thallium-doped cesium io... more Scintillators play an important role in radiation detection and imaging. Thallium-doped cesium iodide (CsI:Tl) and sodium iodide (NaI:Tl) are two of the major scintillators that have been used for many applications for many decades. In this paper, we will present an improved scintillation performance of Bridgman method-grown CsI(Tl) and NaI(Tl) crystals developed by Xtallized Intelligence, Inc. (XI, Inc.), and we will compare the performance with commercially available CsI:Tl and NaI:Tl. In a preliminary testing using MicroFJ−60035−TSV silicon photomultipliers (ON Semiconductor), the newly developed and improved 12.5 × 12.5 × 6 mm3 CsI:Tl crystal has shown an energy resolution of 4.8% (FWHM) at 662 keV, compared to 7.2% obtained by a commercially available CsI:Tl with a size of 12.5 × 12.5 × 25 mm3. The energy resolution of 5.4% (FWHM) at 662 keV is obtained for the newly improved NaI:Tl crystal, compared to 7% obtained by a commercially available ∅1″ × 1″ NaI(Tl). The comparison of...
The mid-infrared fluorescence properties of erbium (Er) doped low-phonon ternary chloride-based c... more The mid-infrared fluorescence properties of erbium (Er) doped low-phonon ternary chloride-based crystals (KPb2Cl5, Cs2HfCl6, CsPbCl3, CsCdCl3) have been investigated. All crystals were grown by vertical Bridgman technique. Following optical excitations at 805 nm and 660 nm, all Er3+ doped chlorides exhibited infrared emissions at ~2750, ~3500, and ~4500 nm at room temperature. The mid-infrared emission at 4500 nm originating from the 4I9/2 → 4I11/2 transition showed long emission lifetime values of ~7.8 ms and ~11.6 ms for Er3+ doped Cs2HfCl6 and CsCdCl3 crystals, respectively. In comparison, Er3+ doped KPb2Cl5 and CsPbCl3 demonstrated shorter lifetimes of ~3 ms and ~1.8 ms, respectively. The temperature dependence of the 4I9/2 decay times was performed for Er3+ doped CsPbCl3 and CsCdCl3 crystals. We observed that the fluorescence lifetimes were nearly independent of the temperature, indicating a negligibly small non-radiative decay rate through multiphonon relaxation, as predicted by the energy gap law for low phonon energy hosts. The room temperature stimulated emission cross-sections for the 4I9/2 → 4I11/2 transition were determined to be in a range of ~0.14-0.54 x 10-20 cm2 for the studied Er doped chloride crystals.
Transparent, crack-free single crystal boules of 1-inch diameter Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (... more Transparent, crack-free single crystal boules of 1-inch diameter Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (CHCB) have been successfully grown using the vertical Bridgman method. Samples sized dia. 23mm×30mm and dia. 23mm×26mm, respectively, are characterized for their optical and scintillation properties. Energy resolutions of 3.5% and 3.7% (FWHM) at 662 keV as well as light yields of 23,000 ph/MeV and 20,000 ph/MeV have been calculated for CHC and CHCB, respectively. Results comparable to previously reported smaller crystals have been obtained. Studies on decay times, non-proportionality, and detector characterization are also reported. (This work was supported in part by U.S. Department of Energy under Grant #DE-SC0015733, U.S. National Science Foundation under Grant #HRD-1547757, and by U.S. National Aeronautics and Space Administration under Grant #NNX16AK42G).
IEEE Nuclear Science Symposuim & Medical Imaging Conference, 2010
... Instrum. Meth. A, vol. 558, no. 2, pp. 497 – 503, 2006. [8] A. Kargar, RB Lowell, MJ Harrison... more ... Instrum. Meth. A, vol. 558, no. 2, pp. 497 – 503, 2006. [8] A. Kargar, RB Lowell, MJ Harrison, and DS McGregor, “The crystal geometry and the aspect ratio effects on spectral performance of CdZnTe Frisch collar device,” in P. Soc. Photo-Opt. Inst., vol. 6706, 2007, p. 67061J. ...
Tl2LiYCl6:Ce (TLYC) is a recently discovered dual mode gamma-ray and neutron scintillator. So far... more Tl2LiYCl6:Ce (TLYC) is a recently discovered dual mode gamma-ray and neutron scintillator. So far small crystals of this composition have been studied, but for practical applications with affordable price, large-scale crystals are required. In this work, we present successful efforts to grow crack-free single crystals with sizes up to ⌀1″ × 5.5″. A variety of experimental techniques were employed to investigate the scintillation properties. A ⌀1″ × 1.2″ TLYC cylinder has a light yield of 25,000 ph/MeV, and its energy resolution is better than 4% at 662 keV. The gamma equivalent energy (GEE) produced by thermal neutron is 1.89 MeVee, along with a neutron induced light yield of 47,000 ph/n. Pulse shape discrimination (PSD) between gamma-rays and neutrons has been successfully shown with a current Figure-of-Merit (FOM) of 2.4. This article explores the crystal growth, scintillation properties, and potential applications of TLYC.
2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015
TlLiLaBr6:Ce (TLLB) and Tl2LiYCl6:Ce (TLYC), new cerium doped-thallium based, dual mode gamma and... more TlLiLaBr6:Ce (TLLB) and Tl2LiYCl6:Ce (TLYC), new cerium doped-thallium based, dual mode gamma and neutron elpasolite scintillation crystals, were discovered by and grown at RMD. Energy resolutions at 662 keV of 5.7% and 4.2% have been measured for TLLB:Ce and TLYC:Ce, respectively. Gamma-neutron pulse shape discrimination (PSD) with TLYC:Ce produces a result with a figure-of-merit (FOM) of 2.
Tl2LiYCl6:Ce (TLYC), a new cerium doped-thallium based, dual mode gamma and neutron elpasolite sc... more Tl2LiYCl6:Ce (TLYC), a new cerium doped-thallium based, dual mode gamma and neutron elpasolite scintillation crystal, has been grown and evaluated at RMD. Energy resolution of 4.2% at 662 keV (FWHM) is measured for samples of this material. From comparison with a 137Cs spectrum collected with NaI:Tl, a gamma-ray induced light yield of 26,000 ph/MeV is estimated for TLYC. The material also shows better proportionality of response than both LaBr3:Ce and NaI:Tl in the energy range between 32 keV to 1275 keV. Single thermal neutron interactions produce a peak measured at a gamma equivalent energy of 1.9 MeVee, corresponding to a (neutron induced) light yield of approximately 47,000 ph/n. Decay times obtained from gamma-ray interactions in TLYC are measured at about 57 ns, 431 ns, and 1055 ns, with slightly shorter values measured for neutron interactions. These differences allow for gamma-neutron pulse shape discrimination (PSD) and a PSD Figure-of-Merit (FOM) of 2 is measured with TLYC.
Abstract Being a high-Z material, mercuric iodide (HgI2) has a relatively high gamma-ray absorpti... more Abstract Being a high-Z material, mercuric iodide (HgI2) has a relatively high gamma-ray absorption coefficient. Its low charge carrier mobilities, however, have somewhat hampered the interest in using this material as a room-temperature gamma-ray spectrometer. By using the Frisch collar technology, the influence of the low charge carrier can be significantly reduced. The growth of HgI2 by the Faile method in a horizontal furnace fortuitously produces tetragonal prismatic crystals. These crystals with appropriate dimensions can be fabricated into Frisch collar spectrometers. With the Frisch collar technology, 1.8% energy resolution for 662-keV gamma rays has been achieved.
Transactions of the American Nuclear Society, 2010
Abstract In this study, the charge collection efficiencies (CCEs) of a 7.8- × 7.8- × 15.6-mm3 CdZ... more Abstract In this study, the charge collection efficiencies (CCEs) of a 7.8- × 7.8- × 15.6-mm3 CdZnTe Frisch collar detector and a 2.1- × 2.1- × 4.1-mm3 HgI2 Frisch collar detector were measured and compared. Two Frisch collar devices were designed and fabricated to have identical aspect ratios of 2.0 to maintain similar weighting potential distributions. Pulse-height spectra were acquired from both Frisch collar devices with a standard calibration gamma-ray source of 137Cs, and the results are presented. As known, the Frisch collar alters the weighting potential within the planar device and enhances the CCE distributions. Thus, the parameters affecting these distributions have great impact on the pulse-height spectrum. The device length and mobility-lifetime product μτ have great impacts on CCE. Primarily, crystal (device) length L directly affects CCE because more charge carriers are trapped in longer devices with longer traveling distances. Alternatively, the better mobility-lifetime product of the charge carriers enhances CCE of the fabricated device. It is shown in this study that as a result of similarity in shape for both devices (equal aspect ratio), the weighting potential distributions resemble each other. However, as a result of the trapping effect (due to both length and μτ), the CCE profiles are not the same, and the CdZnTe detector shows more uniform response to gamma rays and, therefore, better spectroscopic performance (even with a longer device length), which is confirmed through CCE simulations. Finally, by applying the CCE model to the HgI2 Frisch collar device, the mobility-lifetime products μe, h τe, h of electrons and holes were estimated to be 0.0008 and 0.00003 cm2·V–1, respectively, for the HgI2 crystal.
Scintillators play an important role in radiation detection and imaging. Thallium-doped cesium io... more Scintillators play an important role in radiation detection and imaging. Thallium-doped cesium iodide (CsI:Tl) and sodium iodide (NaI:Tl) are two of the major scintillators that have been used for many applications for many decades. In this paper, we will present an improved scintillation performance of Bridgman method-grown CsI(Tl) and NaI(Tl) crystals developed by Xtallized Intelligence, Inc. (XI, Inc.), and we will compare the performance with commercially available CsI:Tl and NaI:Tl. In a preliminary testing using MicroFJ−60035−TSV silicon photomultipliers (ON Semiconductor), the newly developed and improved 12.5 × 12.5 × 6 mm3 CsI:Tl crystal has shown an energy resolution of 4.8% (FWHM) at 662 keV, compared to 7.2% obtained by a commercially available CsI:Tl with a size of 12.5 × 12.5 × 25 mm3. The energy resolution of 5.4% (FWHM) at 662 keV is obtained for the newly improved NaI:Tl crystal, compared to 7% obtained by a commercially available ∅1″ × 1″ NaI(Tl). The comparison of...
The mid-infrared fluorescence properties of erbium (Er) doped low-phonon ternary chloride-based c... more The mid-infrared fluorescence properties of erbium (Er) doped low-phonon ternary chloride-based crystals (KPb2Cl5, Cs2HfCl6, CsPbCl3, CsCdCl3) have been investigated. All crystals were grown by vertical Bridgman technique. Following optical excitations at 805 nm and 660 nm, all Er3+ doped chlorides exhibited infrared emissions at ~2750, ~3500, and ~4500 nm at room temperature. The mid-infrared emission at 4500 nm originating from the 4I9/2 → 4I11/2 transition showed long emission lifetime values of ~7.8 ms and ~11.6 ms for Er3+ doped Cs2HfCl6 and CsCdCl3 crystals, respectively. In comparison, Er3+ doped KPb2Cl5 and CsPbCl3 demonstrated shorter lifetimes of ~3 ms and ~1.8 ms, respectively. The temperature dependence of the 4I9/2 decay times was performed for Er3+ doped CsPbCl3 and CsCdCl3 crystals. We observed that the fluorescence lifetimes were nearly independent of the temperature, indicating a negligibly small non-radiative decay rate through multiphonon relaxation, as predicted by the energy gap law for low phonon energy hosts. The room temperature stimulated emission cross-sections for the 4I9/2 → 4I11/2 transition were determined to be in a range of ~0.14-0.54 x 10-20 cm2 for the studied Er doped chloride crystals.
Transparent, crack-free single crystal boules of 1-inch diameter Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (... more Transparent, crack-free single crystal boules of 1-inch diameter Cs2HfCl6 (CHC) and Cs2HfCl4Br2 (CHCB) have been successfully grown using the vertical Bridgman method. Samples sized dia. 23mm×30mm and dia. 23mm×26mm, respectively, are characterized for their optical and scintillation properties. Energy resolutions of 3.5% and 3.7% (FWHM) at 662 keV as well as light yields of 23,000 ph/MeV and 20,000 ph/MeV have been calculated for CHC and CHCB, respectively. Results comparable to previously reported smaller crystals have been obtained. Studies on decay times, non-proportionality, and detector characterization are also reported. (This work was supported in part by U.S. Department of Energy under Grant #DE-SC0015733, U.S. National Science Foundation under Grant #HRD-1547757, and by U.S. National Aeronautics and Space Administration under Grant #NNX16AK42G).
IEEE Nuclear Science Symposuim & Medical Imaging Conference, 2010
... Instrum. Meth. A, vol. 558, no. 2, pp. 497 – 503, 2006. [8] A. Kargar, RB Lowell, MJ Harrison... more ... Instrum. Meth. A, vol. 558, no. 2, pp. 497 – 503, 2006. [8] A. Kargar, RB Lowell, MJ Harrison, and DS McGregor, “The crystal geometry and the aspect ratio effects on spectral performance of CdZnTe Frisch collar device,” in P. Soc. Photo-Opt. Inst., vol. 6706, 2007, p. 67061J. ...
Tl2LiYCl6:Ce (TLYC) is a recently discovered dual mode gamma-ray and neutron scintillator. So far... more Tl2LiYCl6:Ce (TLYC) is a recently discovered dual mode gamma-ray and neutron scintillator. So far small crystals of this composition have been studied, but for practical applications with affordable price, large-scale crystals are required. In this work, we present successful efforts to grow crack-free single crystals with sizes up to ⌀1″ × 5.5″. A variety of experimental techniques were employed to investigate the scintillation properties. A ⌀1″ × 1.2″ TLYC cylinder has a light yield of 25,000 ph/MeV, and its energy resolution is better than 4% at 662 keV. The gamma equivalent energy (GEE) produced by thermal neutron is 1.89 MeVee, along with a neutron induced light yield of 47,000 ph/n. Pulse shape discrimination (PSD) between gamma-rays and neutrons has been successfully shown with a current Figure-of-Merit (FOM) of 2.4. This article explores the crystal growth, scintillation properties, and potential applications of TLYC.
2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015
TlLiLaBr6:Ce (TLLB) and Tl2LiYCl6:Ce (TLYC), new cerium doped-thallium based, dual mode gamma and... more TlLiLaBr6:Ce (TLLB) and Tl2LiYCl6:Ce (TLYC), new cerium doped-thallium based, dual mode gamma and neutron elpasolite scintillation crystals, were discovered by and grown at RMD. Energy resolutions at 662 keV of 5.7% and 4.2% have been measured for TLLB:Ce and TLYC:Ce, respectively. Gamma-neutron pulse shape discrimination (PSD) with TLYC:Ce produces a result with a figure-of-merit (FOM) of 2.
Tl2LiYCl6:Ce (TLYC), a new cerium doped-thallium based, dual mode gamma and neutron elpasolite sc... more Tl2LiYCl6:Ce (TLYC), a new cerium doped-thallium based, dual mode gamma and neutron elpasolite scintillation crystal, has been grown and evaluated at RMD. Energy resolution of 4.2% at 662 keV (FWHM) is measured for samples of this material. From comparison with a 137Cs spectrum collected with NaI:Tl, a gamma-ray induced light yield of 26,000 ph/MeV is estimated for TLYC. The material also shows better proportionality of response than both LaBr3:Ce and NaI:Tl in the energy range between 32 keV to 1275 keV. Single thermal neutron interactions produce a peak measured at a gamma equivalent energy of 1.9 MeVee, corresponding to a (neutron induced) light yield of approximately 47,000 ph/n. Decay times obtained from gamma-ray interactions in TLYC are measured at about 57 ns, 431 ns, and 1055 ns, with slightly shorter values measured for neutron interactions. These differences allow for gamma-neutron pulse shape discrimination (PSD) and a PSD Figure-of-Merit (FOM) of 2 is measured with TLYC.
Abstract Being a high-Z material, mercuric iodide (HgI2) has a relatively high gamma-ray absorpti... more Abstract Being a high-Z material, mercuric iodide (HgI2) has a relatively high gamma-ray absorption coefficient. Its low charge carrier mobilities, however, have somewhat hampered the interest in using this material as a room-temperature gamma-ray spectrometer. By using the Frisch collar technology, the influence of the low charge carrier can be significantly reduced. The growth of HgI2 by the Faile method in a horizontal furnace fortuitously produces tetragonal prismatic crystals. These crystals with appropriate dimensions can be fabricated into Frisch collar spectrometers. With the Frisch collar technology, 1.8% energy resolution for 662-keV gamma rays has been achieved.
Transactions of the American Nuclear Society, 2010
Abstract In this study, the charge collection efficiencies (CCEs) of a 7.8- × 7.8- × 15.6-mm3 CdZ... more Abstract In this study, the charge collection efficiencies (CCEs) of a 7.8- × 7.8- × 15.6-mm3 CdZnTe Frisch collar detector and a 2.1- × 2.1- × 4.1-mm3 HgI2 Frisch collar detector were measured and compared. Two Frisch collar devices were designed and fabricated to have identical aspect ratios of 2.0 to maintain similar weighting potential distributions. Pulse-height spectra were acquired from both Frisch collar devices with a standard calibration gamma-ray source of 137Cs, and the results are presented. As known, the Frisch collar alters the weighting potential within the planar device and enhances the CCE distributions. Thus, the parameters affecting these distributions have great impact on the pulse-height spectrum. The device length and mobility-lifetime product μτ have great impacts on CCE. Primarily, crystal (device) length L directly affects CCE because more charge carriers are trapped in longer devices with longer traveling distances. Alternatively, the better mobility-lifetime product of the charge carriers enhances CCE of the fabricated device. It is shown in this study that as a result of similarity in shape for both devices (equal aspect ratio), the weighting potential distributions resemble each other. However, as a result of the trapping effect (due to both length and μτ), the CCE profiles are not the same, and the CdZnTe detector shows more uniform response to gamma rays and, therefore, better spectroscopic performance (even with a longer device length), which is confirmed through CCE simulations. Finally, by applying the CCE model to the HgI2 Frisch collar device, the mobility-lifetime products μe, h τe, h of electrons and holes were estimated to be 0.0008 and 0.00003 cm2·V–1, respectively, for the HgI2 crystal.
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