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ABSTRACT: We report on photoconductive detector based on CeF<sub>3</sub> thin films in ultraviolet region. CeF<sub>3</sub> thin films were grown by pulse laser deposition. The sensitivity spectrum of detector shows the response below 310 nm.
Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics, 2009. CLEO/PACIFIC RIM '09. Conference on; 09/2009
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K. Kamada,
T. Yanagida,
K. Tsutsumi,
Y. Usuki,
M. Sato,
H. Ogino,
A. Novoselov,
A. Yoshikawa,
M. Kobayashi,
S. Sugimoto, F. Saito
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ABSTRACT: Pr:LuAG crystals possess interesting properties, such as high density, high light yield, and very fast 5d-4f emission decay time. Recently, we developed a Pr:LuAG single crystal with a diameter of 2 inches for scintillator applications, such as medical imaging. In this study, Pr-doped Lu<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (Pr:LuAG) single crystals with a diameter of 2 inches were grown by means of the Czochralski method; a body length of up to 90 mm was achieved. The Pr:LuAG crystals produced a homogeneous light yield with approximately 2.5 times less intensity compared to that produced by a conventional Ce:LSO crystal. A sample with dimensions of 5 mm times 5 mm times 1 mm exhibited energy resolutions of 4.8% at 662 keV, as measured by using a photomultiplier (PMT: Hamamatsu H6531), and 5.8% at 662 keV, as measured by using an Avalanche photodiode (APD: Hamamatsu S8664-55). The Pr:LuAG crystals exhibited a very fast rise time of approximately 0.4 ns, excited by a pulsed X-ray at room temperature. The decay time was approximately 18 ns, along with a noticeable presence of slower decay components (with a decay time of 55.0 ns). Furthermore, the Pr:LuAG crystals showed good linearity between the energy and pulse height within approximately 4% of the standard deviation in the range from 122 keV (<sup>152</sup>Eu) to 1.4 MeV (<sup>241</sup>Am) .
IEEE Transactions on Nuclear Science 07/2009; · 1.45 Impact Factor
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ABSTRACT: Single crystals of LuAG doped with Pr<sup>3+</sup> ions (0.2 mol%) are grown by the micro-pulling-down (mu-PD) method with an RF heating system. The as-grown crystals are confirmed to be of garnet-type structure with the space group of Ia3d (230). The emission-excitation spectra and luminescence decay kinetics are measured in the temperature range of 5-310 K by using synchrotron radiation as an exciting light source. The intrinsic luminescence is observed at 250 nm at low temperatures. Four emission bands at 308, 325, 360, and 380 nm are ascribed to the 5d-4f transitions of Pr<sup>3+</sup> ions. From the decay kinetics measurements, it is pointed out that there exist two kinds of energy transfer mechanisms from the host LuAG lattice to the Pr<sup>3+</sup> ions. The mechanisms of energy transfer are discussed in connection with the formation of substitution-type defects.
IEEE Transactions on Nuclear Science 07/2008; · 1.45 Impact Factor
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ABSTRACT: (Ce<sub>x</sub>Ca<sub>1-x</sub>)F<sub>2+x</sub> single crystal with x = 0.0001 - 0.03 were grown by the mu-PD method. Ce<sup>3+</sup> doping in CaF<sub>2</sub> lattice gives rise to characteristic absorption and emission bands, which are governed by the characteristics of the isolated Ce<sup>3+</sup>-F<sub>i</sub> <sup>-</sup> C<sub>4v</sub> pair centers and small clusters composed from these pairs. With increasing Ce concentration there is a strong increase of the absorption bands related to the cluster centres, but the radioluminescence spectra are always governed by the emission of the isolated Ce<sup>3+</sup>-F<sub>i</sub> <sup>-</sup> C<sub>4v</sub> pairs without noticeable changes in the emission band shape. Highest radioluminescence intensity is achieved for Ce 0.1{%} concentration and above 1{%} of Ce the onset of concentration quenching is observed. Scintillation response is governed by the energy transfer from the CaF<sub>2</sub> host lattice and even for the Ce3{%} sample the dominant scintillation decay time is about 50{%} longer with respect to the photoluminescence decay time of Ce<sup>3+</sup>-F<sub>i</sub> <sup>-</sup> C<sub>4v</sub> pair centres. Energy transfer processes and the role of different Ce<sup>3+</sup>-based centers are discussed.
IEEE Transactions on Nuclear Science 07/2008; · 1.45 Impact Factor
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ABSTRACT: CeF<sub>3</sub> single crystals heavily doped with Sr<sup>2+</sup> ions are grown by the micro-pulling-down (mu-PD) method. The deviation of the composition in as-grown crystals is found to be entirely negligible. Three dimensional emission-excitation spectra are measured in a wide temperature range of 5-300 K by using synchrotron radiation as an exciting light source. Two intense emission bands are observed at around 320 and 400 nm. The origin of these bands is discussed on the basis of the perturbation effects introduced by Sr doping. It is pointed out that the energy transfer takes place from Ce<sup>3+</sup> sites to defect sites when the crystal is warmed from 5 to 300 K.
IEEE Transactions on Nuclear Science 07/2008; · 1.45 Impact Factor
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ABSTRACT: Effect of Ga substitution in the (Lu,Pr)<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> (Pr :LuAG) scintillator was examined at the crystals grown by the micropulling down (mu-PD) method. Host luminescence due to an exciton localized around the Lu-Al antisite defect was suppressed by Ga admixture. Concentration dependence was investigated and suppression was observed even at the lowest Ga concentration of 5 mol%. Faster decay time as well as less intense slower components were obtained upon increasing the amount of Ga. In the thermostimulated luminescence measurement, the glow curve peaks are gradually shifted to lower temperatures with the gallium admixture, and noticeable intensity decrease was observed only for the (Lu,Pr)<sub>3</sub>(Ga<sub>0.2</sub>Al<sub>0.8</sub>)<sub>5</sub>O<sub>12</sub>. The undesired quenching effect of Ga on the Pr<sup>3+</sup> luminescence seems to be reasonably low up to (Lu,Pr)<sub>3</sub>(Ga<sub>0.2</sub>Al<sub>0.8</sub>)<sub>5</sub>O<sub>12</sub> sample. It is estimated to introduce nonradiative losses of less than 10% with respect to Ga-free Pr:LuAG. Bulk crystals were also grown by the Czochralski (Cz) method and these effects were confirmed.
IEEE Transactions on Nuclear Science 07/2008; · 1.45 Impact Factor
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M. Cadatal,
Minh Pham,
T. Tatsumi,
A. Saiki,
Y. Furukawa,
E. Estacio,
N. Sarukura,
T. Suyama,
K. Fukuda,
Kyoung Jin Kim,
A. Yoshikawa, F. Saito
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ABSTRACT: We report the first successful micro-pulling down method growth and ultraviolet emission from a Ce:LiCAF crystal. With two-side pumping configuration, 23% slope efficiency is obtained from the 290-nm emission of a 30 mm-long, 2 mm-wide Brewster-cut crystal.
Lasers and Electro-Optics, 2008 and 2008 Conference on Quantum Electronics and Laser Science. CLEO/QELS 2008. Conference on; 06/2008
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ABSTRACT: We measure the ac complex resistivity in the mixed state of amorphous MoxSi1−x films with different thicknesses (t). For films with t=100 and 30 nm we can determine the vortex-glass-transition (VGT) line which persists down to low temperatures (T) up to high fields (B) near the upper critical field at T=0. In the liquid phase the vortex-relaxation time (τg) extracted from the frequency dependence of ac resistivity follows the power-law T dependence expected by the VG theory for three dimensions (3D). For the thinner (10, 6 nm) films, both the dc resistivity and τg follow the activated T dependence except for the very low-T region, suggestive of 2D VGT. For all of the films studied, τg in high B shows a decreased T dependence at lower T, indicating the quantum-driven fluctuations.
Physica C Superconductivity · 1.01 Impact Factor
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ABSTRACT: We measured temperature dependence of alpha/gamma-ratio of three sample pieces of Ce 0.5 mol% doped Gd<sub>2</sub>SiO<sub>5</sub> crystalline scintillator, which are cut from different ingots and have a dimension of 24times24times5 mm<sup>3</sup>. The temperature is controlled by a heat bath within plusmn0.5 K at +20, 0, and -20 degrees of Celcius. By using intrinsic activity of <sup>152</sup>Gd 2.14 MeV alpha-ray, it is irradiated uniformly inside the scintillator. To determine alpha/gamma-ratio precisely, we measured input energy and pulse height linearity between 60 keV and 511 keV, at three temperature conditions. Then, we measure the alpha-ray response of the scintillator by a passive rejection any outer backgrounds by Pb and Sn blocks. As a result, alpha/gamma-ratio of 0.5 mol% Ce doped GSO is turned out to be ~0.175, and it showed a gradual temperature dependence of ~0.4 keV/K.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: The present paper shows ionization coefficient ratios, k values, k<sub>t</sub> and k<sub>effs</sub> of reverse-type Si avalanche photodiode. Both of k<sub>eff</sub> and K<sub>1</sub>, tend to increase when APDs are cooled down. The results for k<sub>eff</sub> are 0.0023 plusmn 0.0002 at 20degC, 0.0027 plusmn 0.0003 at 0degC, and 0.0049 plusmn 0.0007 at -20degC. With the result of k<sub>1</sub>, temperature dependency of k-values indicates mean free paths of the carriers for phonon scattering shows different temperature dependency, which is considered to reflect the inner structure of APDs.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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K. Kamada,
K Tsutsumi,
Y Usuki,
T Yanagida,
M Sato,
H Ogino,
A. Novoselov,
A Yoshikawa,
M Kobayashi,
S Sugimoto, F. Saito
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ABSTRACT: Pr:LuAG has interesting properties of high density, high light yield and a very fast 5d-4f emission decay time. Recently we have develop 2-inch-diameter Pr:LuAG single crystal for scintillator applications such medical imaging and high-energy physics. In this report, we study uniformity of the light yield, energy resolution, decay time and gamma-ray response in the range from 59.5 keV (<sup>241</sup>Am) to 1.4 MeV (<sup>241</sup>Am).
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: We developed transparent ceramic scintillators of Ce doped YAG, Ce and Nd codoped YAG, and Ce doped (GdY)AG, respectively. We cut them with a size of 5 times 5 times 5 mm<sup>3</sup> for Ce:YAG and (Ce,Nd):YAG, and 5 times 5 times 2 mm<sup>3</sup> for Ce:GYAG. At three temperature conditions, such as +20, 0, and -20degC, a temperature dependence of a light yield are measured, when they are coupled with avalanche photo diode, which is a S8664-55 type APD manufactured by Hamamatsu photonics. In these conditions, light yield of them turned out to be ~0.4, ~0.1, and ~0.25 times as large as that of Tl:CsI crystal. All of them show little temperature dependence of less than 10% in this 40 K temperature change. By measuring circuit noise and statistical noise due to excess noise factor of APD measurement system, we also study the temperature dependence of intrinsic energy resolution of these scintillators, in the range of 60 to 1400 keV. There are little temperature dependence observed, and it turned out to be about 5% at several hundreds keV.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: In this paper we present a summary of a study of reverse-type avalanche photodiodes (APDs) used as scintillation detectors for X- and gamma-ray spectroscopy. The energy resolution of the APDs was evaluated by varying the avalanche gain, M, in the range from 1 to 200. The best energy resolution recorded for the 662 keV <sup>137</sup>Cs gamma-ray photoabsorption peak was 8.3 plusmn 0.5 % using a 5 times 5 times 5 mm<sup>3</sup> BGO crystal coupled to a S8664-55 APD with a 5 times 5 mm<sup>2</sup> light sensitive window, manufactured by Hamamatsu Photonics, Inc. The measurement was made with a gain of 20 and at a temperature of -20degC. The main advantage of this method is that an accurate value for the intrinsic resolution of the crystal can be easily obtained by subtracting the contribution to the energy resolution from circuit noise and the electron-hole pair statistics. The intrinsic energy resolution of the BGO crystal sample at 662 keV was found to be 6.5 plusmn 0.5%. The observed intrinsic energy resolution of BGO as a function of energy shows the same relationship as that shown in other published works. With this method the intrinsic energy resolution of GSO (Ce 0.5 %mol) was also measured. While the intrinsic energy resolution of BGO shows an energy dependence proportional to E<sup>-1/2</sup>, GSO has a step-like characteristic, with the energy resolution increasing from ~100 keV up to ~500 keV.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: Pr<sup>3+</sup> doped Lu<sub>3</sub>AI<sub>5</sub>O<sub>12</sub> crystalline scintillator is developed. By the gamma-ray irradiation, three different Pr<sup>3+</sup> concentration, 0.1, 0.18, and 0.22 mol%, are compared in a view of light yield, energy resolution, and decay time. At the same time, a temperature dependence of these gamma-ray responses are also investigated. As a result, the 0.22 mol% sample shows the highest light yield, reaching more than three times as large as reference BGO scintillator, at +20 degrees of Celcius. A main component of the decay is ~ 21 ns for all the sample pieces. The temperature dependence of these sample pieces is low. Gamma-ray responses at +20 degrees of Celcius are almost the same level for these three pieces, but the temperature dependences are different with Pr<sup>3+</sup> concentration.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: This paper reports on hole multiplication processes, detected in a reverse-type avalanche photodiode (APD), Hamamatsu Photonics type S8664-55, which has a light sensitive area of 5 times 5 mm and a depletion layer thickness of ~ 40 mum. When the APD was irradiated from a <sup>241</sup>Am isotope, the 13.9 keV and 17.6 keV X-rays produced spectral peaks, whose pulse height depended strongly on the bias voltage, whereas 57.5 keV photons produced another peak, whose the pulse height was much less bias sensitive. The former are identified with electron multiplication signals, whereas the latter with those due to hole multiplication. By measuring the electron and hole multiplication gains as a function of the bias voltage, the ratio of hole and electron ionization probabilities was determined as 0.0130 plusmn 0.0010 at 20degC, and 0.0153 plusmn 0.0010 at -20degC.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
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ABSTRACT: Pr:LuAG have good scintillation properties of high energy resolution, very fast 5d-4f emission decay time, higher density and high light yield. In order to apply Pr:LuAG to medical imaging application such PET and PEM, the optimization of light output and energy resolution of scintillators is very important. Especially Therefore, to choose a suited reflector is very important because Pr:LuAG has short emission wave length at 310 nm. In this work, we studied spatial and energy resolution of pixilated Pr:LuAG with various reflectors (Teflon tape, ESR, BaSO4) by irradiation of <sup>22</sup>Na source. Using the BaSO<sub>4</sub> reflector, the light output has increased by ~210% compared to the ESR reflector, and ~170% compared to the Teflon tape reflector. The BaSO<sub>4</sub> reflector also resulted in the best improvement of the energy resolution up to 12%.
Nuclear Science Symposium Conference Record, 2007. NSS '07. IEEE;
