41 results on '"Keitaro Hitomi"'
Search Results
2. Pulse-height loss in the signal readout circuit of compound semiconductor detectors
- Author
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Mohammad Nakhostin and Keitaro Hitomi
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Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,010308 nuclear & particles physics ,Preamplifier ,business.industry ,Capacitive sensing ,Detector ,Electrostatic induction ,01 natural sciences ,Signal ,Cadmium telluride photovoltaics ,0103 physical sciences ,Optoelectronics ,010306 general physics ,business ,Instrumentation ,Digital signal processing ,Energy (signal processing) - Abstract
Compound semiconductor detectors such as CdTe, CdZnTe, HgI2 and TlBr are known to exhibit large variations in their charge collection times. This paper considers the effect of such variations on the measurement of induced charge pulses by using resistive feedback charge-sensitive preamplifiers. It is shown that, due to the finite decaytime constant of the preamplifiers, the capacitive decay during the signal readout leads to a variable deficit in the measurement of ballistic signals and a digital pulse processing method is employed to correct for it. The method is experimentally examined by using sampled pulses from a TlBr detector coupled to a charge-sensitive preamplifier with 150 μs of decay-time constant and 20 % improvement in the energy resolution of the detector at 662 keV is achieved. The implications of the capacitive decay on the correction of charge-trapping effect by using depth-sensing technique are also considered.
- Published
- 2018
3. Fabrication of double-sided thallium bromide strip detectors
- Author
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Keizo Ishii, Tatsuya Ito, Toshiyuki Onodera, Keitaro Hitomi, Nobumichi Nagano, and Seong Yun Kim
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Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,Astrophysics::High Energy Astrophysical Phenomena ,chemistry.chemical_element ,Electron ,STRIPS ,01 natural sciences ,Spectral line ,030218 nuclear medicine & medical imaging ,law.invention ,03 medical and health sciences ,0302 clinical medicine ,law ,0103 physical sciences ,Instrumentation ,Physics ,010308 nuclear & particles physics ,business.industry ,Detector ,Gamma ray ,Full width at half maximum ,chemistry ,Electrode ,Optoelectronics ,Thallium ,business - Abstract
Double-sided strip detectors were fabricated from thallium bromide (TlBr) crystals grown by the traveling-molten zone method using zone-purified materials. The detectors had three 3.4-mm-long strips with 1-mm widths and a surrounding electrode placed orthogonally on opposite surfaces of the crystals at approximately 6.5×6.5 mm2 in area and 5 mm in thickness. Excellent charge transport properties for both electrons and holes were observed from the TlBr crystals. The mobility-lifetime products for electrons and holes in the detector were measured to be ~3×10−3 cm2/V and ~1×10−3 cm2/V, respectively. The 137Cs spectra corresponding to the gamma-ray interaction position were obtained from the detector. An energy resolution of 3.4% of full width at half maximum for 662-keV gamma rays was obtained from one “pixel” (an intersection of the strips) of the detector at room temperature.
- Published
- 2016
4. Experimental Determination of the Ionization Energy in TlBr
- Author
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Tadayoshi Shoji, Keitaro Hitomi, Toshiyuki Onodera, Seong Yun Kim, and Keizo Ishii
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Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Detector ,Gamma ray ,Photodiode ,law.invention ,Semiconductor detector ,Optics ,Nuclear Energy and Engineering ,law ,Ionization ,Gamma ray detectors ,Electrical and Electronic Engineering ,Atomic physics ,Ionization energy ,business - Abstract
The average ionization energy required to excite an electron-hole pair in TlBr was estimated to be $5.50 \pm 0.05~\hbox{eV}$ by comparing the peak position of 59.5-keV gamma rays obtained from four pixels of a pixelated TlBr detector to the peak position obtained from a Si PIN photodiode at room temperature.
- Published
- 2015
5. Characterization of pixelated TlBr detectors with Tl electrodes
- Author
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Toshiyuki Onodera, Keizo Ishii, Keitaro Hitomi, T. Shoji, and Seong Yun Kim
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Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,business.industry ,Detector ,Gamma ray ,chemistry.chemical_element ,Electron ,Anode ,Crystal ,Full width at half maximum ,Optics ,chemistry ,Electrode ,Thallium ,High Energy Physics::Experiment ,business ,Instrumentation - Abstract
A 4.36-mm-thick pixelated thallium bromide (TlBr) detector with Tl electrodes was fabricated from a crystal grown by the traveling molten zone method using zone-purified material. The detector had four 1×1 mm2 pixelated anodes. The detector performance was characterized at room temperature. The mobility-lifetime products of electrons for each pixel of the TlBr detector were measured to be >2.8×10−3 cm2/V. The four pixelated anodes of the detector exhibited energy resolutions of 1.5–1.8% full width at half maximum (FWHM) for 662-keV gamma rays for single-pixel events with the depth correction method. An energy resolution of 4.5% FWHM for 662-keV gamma rays was obtained from a reconstructed energy spectrum using two-pixel events from the two pixelated anodes on the detector.
- Published
- 2014
6. Recent results from pixelated TlBr detectors with Tl electrodes operated at room-temperature
- Author
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Sean O'Neal, Charles Leak, William Koehler, Zhong He, and Keitaro Hitomi
- Subjects
010302 applied physics ,Physics ,010308 nuclear & particles physics ,business.industry ,Preamplifier ,Detector ,01 natural sciences ,Cathode ,law.invention ,Full width at half maximum ,law ,Electrical resistivity and conductivity ,0103 physical sciences ,Electrode ,Optoelectronics ,Gamma spectroscopy ,Polarization (electrochemistry) ,business - Abstract
Thallium-bromide (TlBr) is a viable alternative to CZT for room-temperature gamma ray spectroscopy because of its high atomic number, high density, and wide band-gap. Sub-1% FWHM energy resolution at 662 keV has been achieved on 5 mm thick pixelated devices, however, these results are mostly limited to stable operation at −20°C. During room-temperature operation, the devices degrade and fail, a phenomenon known as polarization. Polarization is likely caused by bulk-to-contact interactions facilitated by ionic conduction. In 2008, Hitomi et al. found that room-temperature lifetime could be extended by applying Tl electrodes. In this work we verify stable room-temperature performance of a 4.1 mm thick pixelated TlBr detector with Tl electrodes. Energy resolution, mobility-lifetime product, and resistivity are characterized and presented. Resolutions of 1.6% and 1.2% FWHM are achieved for all depths and cathode-side events only, respectively. A very high electron mobility-lifetime product is calculated: 3.1±0.2 ·10-2 cm2/V.
- Published
- 2016
7. Timing Performance of TlBr Detectors
- Author
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Toshiyuki Onodera, T. Shoji, Keitaro Hitomi, Keizo Ishii, T. Tada, Seong Yun Kim, and Yuanlai Xu
- Subjects
Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Detector ,Biasing ,Scintillator ,Cathode ,law.invention ,Full width at half maximum ,Optics ,Nuclear Energy and Engineering ,law ,Electrode ,High Energy Physics::Experiment ,Irradiation ,Electrical and Electronic Engineering ,Oscilloscope ,business - Abstract
The timing performance of TlBr detectors was evaluated at room temperature (22 °C). 0.5-mm-thick planar TlBr detectors with Tl circular electrodes with a diameter of 3 mm were fabricated from TlBr crystals grown by the traveling molten zone method using a zone-purified material. The pulse rise time of the TlBr detector was measured using a digital oscilloscope as the cathode surface of the device was irradiated with a 22Na gamma-ray source. Coincidence timing spectra were obtained between the TlBr detector and a BaF2 scintillation detector when both detectors were irradiated with 511 keV positron annihilation gamma-rays. The timing resolution of the TlBr detector was found to be inversely proportional to the applied bias voltage. The TlBr detector, in coincidence with the BaF2 detector, exhibited timing resolutions characterized by a 6.5 ns full width at half maximum (FWHM) and an 8.5 ns FWHM with and without an energy window of 350 keV-560 keV, respectively.
- Published
- 2013
8. TlBr Capacitive Frisch Grid Detectors
- Author
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Yuanlai Xu, T. Tada, Toshiyuki Onodera, T. Shoji, Keitaro Hitomi, Keizo Ishii, and Seong Yun Kim
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Physics ,Nuclear and High Energy Physics ,Fano factor ,Physics::Instrumentation and Detectors ,Preamplifier ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Capacitive sensing ,Resolution (electron density) ,Detector ,Wide-bandgap semiconductor ,Full width at half maximum ,Optics ,Nuclear Energy and Engineering ,Nuclear electronics ,Optoelectronics ,High Energy Physics::Experiment ,Electrical and Electronic Engineering ,business - Abstract
Capacitive Frisch grid detectors with the dimensions of 2 mm × 2 mm × 4.4 mm were fabricated from TlBr crystals grown by the travelling molten zone method using zone-purified materials. Spectroscopic performance of the detectors was evaluated at room temperature (24°C), - 5°C and - 20°C. The TlBr detector exhibited an energy resolution of 1.6% FWHM at 662 keV with a peak-to-Compton ratio of 8.7 with the depth correction at room temperature. Improvement of the detector performance was achieved by cooling the detector-preamplifier system. The energy resolutions of 3.4%, 1.5%, 1.0% and 0.9% FWHM at 122 keV, 356 keV, 662 keV and 1332 keV, respectively, were recorded with the TlBr detector without the depth correction at - 5°C. An energy resolution of 0.9% FWHM at 662 keV with a peak-to-Compton ratio of 18.2 was obtained from the TlBr detector with the depth correction at -20°C. An upper limit for the Fano factor of TlBr was estimated to be 0.43 at -20°C.
- Published
- 2013
9. Digital pulse processing for planar TlBr detectors, optimized for ballistic deficit and charge-trapping effect
- Author
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Keitaro Hitomi and Mohammad Nakhostin
- Subjects
Physics ,Nuclear and High Energy Physics ,business.industry ,Pulse (signal processing) ,Resolution (electron density) ,Detector ,Charge (physics) ,Trapping ,Optics ,Planar ,business ,Instrumentation ,Digital signal processing ,Energy (signal processing) - Abstract
The energy resolution of thallium bromide (TlBr) detectors is significantly limited by charge-trapping effect and pulse ballistic deficit, caused by the slow charge collection time. A digital pulse processing algorithm has been developed aiming to compensate for charge-trapping effect, while minimizing pulse ballistic deficit. The algorithm is examined using a 1 mm thick TlBr detector and an excellent energy resolution of 3.37% at 662 keV is achieved at room temperature. The pulse processing algorithms are presented in recursive form, suitable for real-time implementations.
- Published
- 2012
10. K-mean clustering algorithm for processing signals from compound semiconductor detectors
- Author
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T. Tada, Keizo Ishii, Yan Wu, Keitaro Hitomi, Seong Yun Kim, and Hiromichi Yamazaki
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Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,business.industry ,Detector ,k-means clustering ,Signal ,Full width at half maximum ,Optics ,Waveform ,business ,Cluster analysis ,Instrumentation ,Digital signal processing ,Energy (signal processing) - Abstract
The K-mean clustering algorithm was employed for processing signal waveforms from TlBr detectors. The signal waveforms were classified based on its shape reflecting the charge collection process in the detector. The classified signal waveforms were processed individually to suppress the pulse height variation of signals due to the charge collection loss. The obtained energy resolution of a 137 Cs spectrum measured with a 0.5 mm thick TlBr detector was 1.3% FWHM by employing 500 clusters.
- Published
- 2011
11. Recent Development of TlBr Gamma-Ray Detectors
- Author
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Seong Yun Kim, Keitaro Hitomi, T. Tada, Yan Wu, Keizo Ishii, Tomonobu Tanaka, Tadayoshi Shoji, and Hiromichi Yamazaki
- Subjects
Physics ,Nuclear and High Energy Physics ,Zone melting ,Physics::Instrumentation and Detectors ,business.industry ,Resolution (electron density) ,Detector ,Scintillator ,Temperature measurement ,Anode ,Full width at half maximum ,Planar ,Optics ,Nuclear Energy and Engineering ,Electrode ,High Energy Physics::Experiment ,Electrical and Electronic Engineering ,business - Abstract
Planar detectors, strip detectors and double-sided strip detectors were fabricated from TlBr crystals grown by the traveling molten zone method using zone-purified material. The detector performance including the leakage current, energy resolutions and timing performance were evaluated in order to assess the capability of the detectors for PET and SPECT applications. The TlBr detectors exhibited excellent spectroscopic performance at room temperature. An energy resolution of 3.4% FWHM at 511 keV was obtained from a TlBr planar detector 1 mm thick. A TlBr strip detector 1 mm thick with four anode strip electrodes exhibited almost uniform detector performance over the strips with the average energy resolution of 4.4% FWHM at 511 keV. A TlBr double-sided strip detector exhibited an energy resolution of 6.3% FWHM for 122 keV gamma-rays. Coincidence timing spectra between a TlBr planar detector and a BaF 2 scintillation detector were recorded at room temperature. Timing resolutions of 14 ns and 24 ns were obtained from TlBr detectors 0.5 mm and 1 mm thick, respectively. By cooling the detector to 0 oC, an improved timing resolution of 12 ns was obtained from a TlBr detector 1 mm thick.
- Published
- 2011
12. Digital pulse processing and electronic noise analysis for improving energy resolutions in planar TlBr detectors
- Author
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Keizo Ishii, Yan Wu, Keitaro Hitomi, Seong Yun Kim, Hiromichi Yamazaki, T. Tada, and Tomonobu Tanaka
- Subjects
Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,business.industry ,Detector ,Resolution (electron density) ,8-bit ,Pulse shaping ,Pulse (physics) ,Full width at half maximum ,Planar ,Optics ,High Energy Physics::Experiment ,business ,Instrumentation ,Energy (signal processing) - Abstract
Digital pulse processing and electronic noise analysis are proposed for improving energy resolution in planar thallium bromide (TlBr) detectors. An energy resolution of 5.8% FWHM at 662 keV was obtained from a 0.5 mm thick planar TlBr detector at room temperature using a digitizer with a sampling rate of 100 MS/s and 8 bit resolution. The electronic noise in the detector–preamplifier system was measured as a function of pulse shaping time in order to investigate the optimum shaping time for the detector. The depth of interaction (DOI) in TlBr detectors for incident gamma-rays was determined by taking the ratio of pulse heights for fast-shaped to slow-shaped signals. FWHM energy resolution of the detector was improved from 5.8% to 4.2% by implementing depth correction and by using the obtained optimum shaping time.
- Published
- 2011
13. Development of a new two-dimensional position-sensitive detection based on resistive charge division and using CdTe detectors for a high-resolution semiconductor-based PET scanning
- Author
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Yohei Kikuchi, Hiromichi Yamazaki, Atsuki Terakawa, Keizo Ishii, Ken Takahashi, Keitaro Hitomi, Shigeo Matsuyama, and K. Nakamura
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Physics ,Nuclear and High Energy Physics ,Resistive touchscreen ,Fabrication ,business.industry ,Resolution (electron density) ,Detector ,Semiconductor detector ,Full width at half maximum ,Semiconductor ,Optics ,business ,Instrumentation ,Image resolution - Abstract
A new position-sensitive detection technique for semiconductor detector fabrication was developed for a high-spatial-resolution PET scanner with CdTe detectors. We constructed a two-dimensional sensitive CdTe detector with a size of 20×9.5×1.0 mm 3 , of which one side had 1 mm wide resistive strip anodes. Using our method, we succeeded in obtaining a linear presentation of a two-dimensional detection image from a distorted detection image. We showed that the detection positioning within a width of 1.2 mm for the x -axis was obtained with a confidence level of 0.98, and a spatial resolution of approximately 1 mm FWHM was obtained for the y -position. Our newly developed position-sensitive detector will enable the construction of a high-performance PET scanner due to the detector's high spatial resolution and good sensitivity; such a PET scanner is now under construction in our laboratory.
- Published
- 2011
14. Energy-discriminating X-ray computed tomography system utilizing a cadmium telluride detector
- Author
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Kiyomi Takahasi, Shigehiro Sato, Jun Onagawa, Purkhet Abderyim, Keitaro Hitomi, Eiichi Sato, Manabu Watanabe, Toshiyuki Enomoto, and Akira Ogawae
- Subjects
Physics ,Nuclear and High Energy Physics ,Photon ,business.industry ,Physics::Medical Physics ,Detector ,Contrast resolution ,Photon energy ,Cadmium telluride photovoltaics ,Photon counting ,Optics ,Absorbed dose ,Tomography ,business ,Instrumentation - Abstract
An energy-discriminating K-edge X-ray computed tomography (CT) system is useful for increasing contrast resolution of a target region utilizing contrast media and for reducing the absorbed dose for patients. The CT system is of the first-generation type with a cadmium telluride (CdTe) detector, and a projection curve is obtained by translation scanning using the CdTe detector in conjunction with an x-stage. An object is rotated by the rotation step angle using a turntable between the translation scans. Thus, CT is carried out by repeating the translation scanning and the rotation of an object. Penetrating X-ray photons from the object are detected by the CdTe detector, and event signals of X-ray photons are produced using charge-sensitive and shaping amplifiers. Both the photon energy and the energy width are selected by use of a multi-channel analyzer, and the number of photons is counted by a counter card. Demonstration of enhanced iodine K-edge X-ray CT was carried out by selecting photons with energies just beyond the iodine K-edge energy of 33.2 keV.
- Published
- 2010
15. Demonstration of iodine K-edge imaging by use of an energy-discrimination X-ray computed tomography system with a cadmium telluride detector
- Author
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Toshiyuki Enomoto, Purkhet Abderyim, Masashi Kameda, Jun Onagawa, Hidezo Mori, Etsuro Tanaka, Eiichi Sato, Toshiaki Kawai, Shigehiro Sato, Akira Ogawa, Manabu Watanabe, Keitaro Hitomi, Abulajiang Abudurexiti, and Kiyomi Takahashi
- Subjects
Photon ,Physical Therapy, Sports Therapy and Rehabilitation ,Photon energy ,Radiation Dosage ,Dogs ,Optics ,Cadmium Compounds ,Animals ,Humans ,Radiology, Nuclear Medicine and imaging ,Ear Neoplasms ,Physics ,Radiation ,Phantoms, Imaging ,business.industry ,Contrast resolution ,Detector ,Heart ,General Medicine ,Cadmium telluride photovoltaics ,Photon counting ,K-edge ,Rabbits ,Tomography ,Tellurium ,Tomography, X-Ray Computed ,business ,Iodine - Abstract
An energy-discrimination K-edge X-ray computed tomography (CT) system is useful for increasing the contrast resolution of a target region by utilizing contrast media. The CT system has a cadmium telluride (CdTe) detector, and a projection curve is obtained by linear scanning with use of the CdTe detector in conjunction with an X-stage. An object is rotated by a rotation step angle with use of a turntable between the linear scans. Thus, CT is carried out by repetition of the linear scanning and the rotation of an object. Penetrating X-ray photons from the object are detected by the CdTe detector, and event signals of X-ray photons are produced with use of charge-sensitive and shaping amplifiers. Both the photon energy and the energy width are selected by use of a multi-channel analyzer, and the number of photons is counted by a counter card. For performing energy discrimination, a low-dose-rate X-ray generator for photon counting was developed; the maximum tube voltage and the minimum tube current were 110 kV and 1.0 microA, respectively. In energy-discrimination CT, the tube voltage and the current were 60 kV and 20.0 microA, respectively, and the X-ray intensity was 0.735 microGy/s at 1.0 m from the source and with a tube voltage of 60 kV. Demonstration of enhanced iodine K-edge X-ray CT was carried out by selection of photons with energies just beyond the iodine K-edge energy of 33.2 keV.
- Published
- 2010
16. Improvement of energy resolutions in TlBr detectors
- Author
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Yohei Kikuchi, Keitaro Hitomi, Tadayoshi Shoji, and Keizo Ishii
- Subjects
Physics ,Nuclear and High Energy Physics ,Physics::Instrumentation and Detectors ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Amplifier ,Detector ,Signal ,Semiconductor detector ,Full width at half maximum ,Integrator ,Electrode ,Optoelectronics ,High Energy Physics::Experiment ,business ,Instrumentation ,Energy (signal processing) - Abstract
Improvement of energy resolutions in thallium bromide (TlBr) detectors was achieved by using a gated integrator in the post amplifier stage. An energy resolution of 4.8% FWHM at 662 keV was obtained from a TlBr detector 1 mm thick at room temperature. The depth of interaction (DOI) in TlBr detectors for incident gamma-rays was determined by taking the Gaussian shaping amplifier signal to gated integrator signal ratio. The energy resolution of the detector was improved from 4.8% to 3.8% FWHM by implementation of the depth correction. The device exhibited an energy resolution of 3.3% FWHM at 662 keV by selecting gamma-ray interaction events in the detector. Long-term stability of a TlBr detector 0.36 mm thick with Tl electrode was also evaluated at room temperature. The detector operated stably for 600 h without significant performance degradations.
- Published
- 2009
17. Influence of zone purification process on TlBr crystals for radiation detector fabrication
- Author
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Keitaro Hitomi, Tadayoshi Shoji, and Toshiyuki Onodera
- Subjects
Physics ,Nuclear and High Energy Physics ,Zone melting ,Fabrication ,business.industry ,technology, industry, and agriculture ,chemistry.chemical_element ,Particle detector ,Semiconductor detector ,chemistry.chemical_compound ,chemistry ,Bromide ,Electrical resistivity and conductivity ,Impurity ,Optoelectronics ,Thallium ,business ,Instrumentation - Abstract
Thallium bromide (TlBr) is a wide gap compound semiconductor and is a promising material for fabrication of nuclear radiation detectors. In this study, the conventional zone refining method was employed to reduce the concentration of impurities in the TlBr crystals. In order to evaluate the efficiency of the zone purification, the zone purification process was repeated up to 300 times. The resistivity, the charge transport properties, and the spectroscopic performance of TlBr detectors fabricated from the crystals zone purified 1 time, 100 times, and 300 times were compared in this study in order to clarify the effectiveness of the zone purification process.
- Published
- 2007
18. Pixellated TlBr detectors with the depth sensing technique
- Author
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Keitaro Hitomi, Tadayoshi Shoji, Zhong He, and Toshiyuki Onodera
- Subjects
Physics ,Nuclear and High Energy Physics ,business.industry ,Resolution (electron density) ,Detector ,chemistry.chemical_element ,Semiconductor detector ,Full width at half maximum ,Optics ,chemistry ,Thallium ,business ,Instrumentation ,Energy (signal processing) - Abstract
The depth sensing technique has been introduced to a 1.8 mm thick pixellated thallium bromide (TlBr) detector in order to enhance the performance of the device. Significant improvement of the energy resolution has been achieved with the device. An energy resolution of 2% FWHM at 662 keV was recorded with the device after the depth correction and rejection.
- Published
- 2007
19. Pixellated thallium bromide detectors for gamma-ray spectroscopy and imaging
- Author
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Toshiyuki Onodera, Yukio Hiratate, Keitaro Hitomi, and Tadayoshi Shoji
- Subjects
Physics ,Nuclear and High Energy Physics ,business.industry ,Detector ,Wide-bandgap semiconductor ,Particle detector ,Cathode ,Cadmium telluride photovoltaics ,law.invention ,Semiconductor detector ,Full width at half maximum ,law ,Optoelectronics ,Gamma spectroscopy ,business ,Instrumentation - Abstract
Recently, pixellated semiconductor detectors exhibit high-energy resolution, which have been studied actively and fabricated from CdTe, CZT and HgI 2 . Thallium bromide (TlBr) is a compound semiconductor characterized with its high atomic numbers (Tl = 81, Br = 35) and high density (7.56 g/cm 2 ). Thus, TlBr exhibits higher photon stopping power than other semiconductor materials used for radiation detector fabrication such as CdTe, CZT and HgI 2 . The wide band gap of TlBr (2.68 eV) permits the detectors low-noise operation at around room temperature. Our studies made an effort to fabricate pixellated TlBr detectors had sufficient detection efficiency and good charge collection efficiency. In this study, pixellated TlBr detectors were fabricated from the crystals purified by the multipass zone-refining method and grown by the horizontal traveling molten zone (TMZ) method. The TlBr detector has a continuous cathode over one crystal surface and 3 x 3 pixellated anodes (0.57 x 0.57 mm 2 each) surrounded by a guard ring on the opposite surface. The electrodes were realized by vacuum evaporation of palladium through a shadow mask. Typical thickness of the detector was 2 mm. Spectrometric performance of the TlBr detectors was tested by irradiating them with 2 4 1 Am (59.5 keV), 5 7 Co (122keV) and 1 3 7 Cs (662keV) gamma-ray sources at temperature of -20°C. Energy resolutions (FWHM) were measured to be 4.0, 6.0 and 9.7 keV for 59.5, 122 and 662 keV gamma-rays, respectively.
- Published
- 2004
20. Thallium bromide optical and radiation detectors for X-ray and gamma-ray spectroscopy
- Author
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Y. Hiratate, Tadayoshi Shoji, M. Matsumoto, Keitaro Hitomi, and O. Muroi
- Subjects
Physics ,Nuclear and High Energy Physics ,X-ray spectroscopy ,Scintillation ,Physics::Instrumentation and Detectors ,business.industry ,X-ray ,Physics::Optics ,Particle detector ,Semiconductor detector ,Nuclear Energy and Engineering ,Optoelectronics ,High Energy Physics::Experiment ,Quantum efficiency ,Gamma spectroscopy ,Electrical and Electronic Engineering ,business ,Spectroscopy - Abstract
Compound semiconductor, thallium bromide (TlBr), has been investigated as an optical and radiation detector material for use in X- and /spl gamma/-ray spectroscopy. Single crystals of TlBr have been grown by the traveling molten zone method using zone-purified materials. Direct X- and /spl gamma/-ray detectors have been fabricated from the TlBr crystals. The direct TlBr detectors have exhibited good spectrometric performances at room temperature. Polarization in TlBr detectors has been observed to deteriorate detector performance. Optical detectors for scintillation spectroscopy have been fabricated from the crystals by depositing an optically transparent electrode of indium-tin-oxide (ITO) on the front surface of the crystals. Quantum efficiency of the TlBr optical detectors has been high in wavelength region below /spl sim/460 nm where scintillation emissions of LSO and GSO occur.
- Published
- 2002
21. Recent progress in thallium bromide detectors for X- and γ-ray spectroscopy
- Author
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R. Hirabuki, Keitaro Hitomi, Yukio Hiratate, M. Matsumoto, Tadayoshi Shoji, T. Suehiro, and O. Muroi
- Subjects
Physics ,Nuclear and High Energy Physics ,Photomultiplier ,Physics::Instrumentation and Detectors ,business.industry ,Resolution (electron density) ,Detector ,Electron ,Scintillator ,Full width at half maximum ,Optoelectronics ,High Energy Physics::Experiment ,business ,Spectroscopy ,Instrumentation ,Image resolution - Abstract
Recent progress in the development of room-temperature TlBr detectors is presented. Higher-performance TlBr detectors have been fabricated from high-purity TlBr crystals grown by the traveling molten zone method. The TlBr crystals have exhibited large mobility–lifetime products of 2.6×10 −4 and 3.7×10 −5 cm 2 /V for electrons and holes, respectively. An energy resolution of 29.8 keV (5.8%) FWHM has been recorded for 511 keV γ-rays with a TlBr detector at room temperature. Timing properties of the TlBr detectors have been studied by recording the coincidence timing spectra between a TlBr detector and a BaF 2 scintillator coupled to a photomultiplier tube. Timing resolution of 21.3 ns FWHM has been measured for 511 keV positron annihilation γ-rays from a 22 Na source. By using a single TlBr detector in current mode, an X-ray CT scanner system of a first-generation type has been developed. The performance of the system has been evaluated by observing tomographic images. Images with good spatial resolution have been obtained by the scanner with the TlBr detector.
- Published
- 2001
22. Thallium bromide photodetectors for scintillation detection
- Author
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O. Muroi, Hiroyuki Ishibashi, Mitsuru Ishii, Y. Hiratate, Keitaro Hitomi, and Tadayoshi Shoji
- Subjects
Physics ,Nuclear and High Energy Physics ,Scintillation ,Physics::Instrumentation and Detectors ,business.industry ,Radioactive source ,Physics::Optics ,Photodetector ,Phosphor ,Scintillator ,Particle detector ,Optics ,Scintillation counter ,Optoelectronics ,Quantum efficiency ,business ,Instrumentation - Abstract
A wide bandgap compound semiconductor, TlBr, has been investigated as a blue sensitive photodetector material for scintillation detection. The TlBr photodetectors have been fabricated from the TlBr crystals grown by the TMZ method using materials purified by many pass zone refining. The performance of the photodetectors has been evaluated by measuring their leakage current, quantum efficiency, spatial uniformity, direct X-ray detection and scintillation detection characteristics. The photodetectors have shown high quantum efficiency for the blue wavelength region and high spatial uniformity for their optical response. In addition, good direct X-ray detection characteristics with an energy resolution of 4.5 keV FWHM for 22 keV X-rays from a 109 Cd radioactive source have been obtained. Detection of blue scintillation from GSO and LSO scintillators irradiated with a 22 Na radioactive source has been done successfully by using the photodetectors at room temperature. A clear full-energy peak for 511 keV γ-rays has been obtained with the TlBr photodetector coupled to the LSO scintillator with an energy resolution of 40% FWHM.
- Published
- 2000
23. Temperature characteristics of the radiation detector using the TlBr crystals
- Author
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Y. Hiratate, O. Muroi, T. Suehiro, Keitaro Hitomi, and Tadayoshi Shoji
- Subjects
Physics ,Nuclear and High Energy Physics ,business.industry ,Analytical chemistry ,Transit time ,Electron ,Activation energy ,Particle detector ,Full width at half maximum ,Nuclear Energy and Engineering ,Electrical resistivity and conductivity ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Gamma detection - Abstract
The radiation detector was fabricated from the TlBr crystals grown by the TMZ (travelling molten zone) method and the FWHM and transit time of electrons and holes were measured as a function of temperature. The TlBr radiation detector shows the best response characteristics at about 313 K (3.19 K/sup -1/) in cases where holes mainly contributed to the output pulses. However, for temperatures higher than 300 K (3.33 K/sup -1/), the FWHM for /sup 241/Am /spl alpha/-particles (5.48 MeV) becomes worse. An activation energy of about 0.90 eV has been deduced from the resistivity measurement.
- Published
- 1999
24. Room temperature X- and gamma-ray detectors using thallium bromide crystals
- Author
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Tadayoshi Shoji, Y. Hiratate, Keitaro Hitomi, O. Muroi, and T. Suehiro
- Subjects
Physics ,Nuclear and High Energy Physics ,Thermoelectric cooling ,Physics::Instrumentation and Detectors ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Resolution (electron density) ,Detector ,Wide-bandgap semiconductor ,chemistry.chemical_element ,Stopping power ,Full width at half maximum ,chemistry ,Thallium ,Optoelectronics ,High Energy Physics::Experiment ,business ,Instrumentation ,Noise (radio) - Abstract
Thallium bromide (TlBr) is a compound semiconductor with wide band gap (2.68 eV) and high X- and γ-ray stopping power. The TlBr crystals were grown by the horizontal travelling molten zone (TMZ) method using purified material. Two types of room temperature X- and γ-ray detectors were fabricated from the TlBr crystals: TlBr detectors with high detection efficiency for positron annihilation γ-ray (511 keV) detection and TlBr detectors with high-energy resolution for low-energy X-ray detection. The detector of the former type demonstrated energy resolution of 56 keV FWHM (11%) for 511 keV γ-rays. Energy resolution of 1.81 keV FWHM for 5.9 keV was obtained from the detector of the latter type. In order to analyze noise characteristics of the detector-preamplifier assembly, the equivalent noise charge (ENC) was measured as a function of the amplifier shaping time for the high-resolution detector. This analysis shows that parallel white noise and 1/f noise were dominant noise sources in the detector system. Current–voltage characteristics of the TlBr detector with a small Peltier cooler were also measured. Significant reduction of the detector leakage current was observed for the cooled detectors.
- Published
- 1999
25. Improved spectrometric characteristics of thallium bromide nuclear radiation detectors
- Author
-
Tadayoshi Shoji, Keitaro Hitomi, Y. Hiratate, T. Murayama, and T. Suehiro
- Subjects
Physics ,Nuclear and High Energy Physics ,Zone melting ,Physics::Instrumentation and Detectors ,business.industry ,Detector ,Wide-bandgap semiconductor ,Analytical chemistry ,chemistry.chemical_element ,Particle detector ,Crystal ,Full width at half maximum ,Optics ,chemistry ,Electrical resistivity and conductivity ,Thallium ,business ,Instrumentation - Abstract
Thallium bromide (TlBr) is a compound semiconductor with a high atomic number and wide band gap. In this study, nuclear radiation detectors have been fabricated from the TlBr crystals. The TlBr crystals were grown by the horizontal travelling molten zone (TMZ) method using the materials purified by many pass zone refining. The crystals were characterized by measuring the resistivity, the mobility–lifetime (μτ) product and the energy required to create an electron–hole pair (the e value). Improved energy resolution has been obtained by the TlBr radiation detectors. At room temperature the full-width at half-maximum (FWHM) for the 59.5, 122 and 662 keV γ-ray photo peak obtained from the detectors were 3.3, 8.8 and 29.5 keV, respectively. By comparing the saturated peak position of the TlBr detector with that of the CdTe detector, the e value has been estimated to be about 5.85 eV for the TlBr crystal.
- Published
- 1999
26. Investigation of pixelated TlBr gamma-ray spectrometers with the depth-sensing technique
- Author
-
Toshiyuki Onodera, Zhong He, Tadayoshi Shoji, and Keitaro Hitomi
- Subjects
Physics ,Nuclear and High Energy Physics ,Spectrometer ,business.industry ,Resolution (electron density) ,Detector ,Gamma ray ,chemistry.chemical_element ,Cathode ,law.invention ,Semiconductor detector ,Full width at half maximum ,Optics ,chemistry ,law ,Thallium ,business ,Instrumentation - Abstract
Pixelated thallium bromide (TlBr) detectors with a thickness of 4.2 mm have been fabricated and investigated with the depth-sensing technique. The energy resolution of the device was improved from 1.95% FWHM to 1.25% FWHM at 662 keV by implementation of the depth correction. The device exhibited an energy resolution of 1.03% FWHM at 662 keV by selecting gamma-ray interaction events occurring underneath the cathode.
- Published
- 2008
27. A method for suppressing polarization phenomena in TlBr detectors
- Author
-
Yoshio Niizeki, Keitaro Hitomi, and T. Shoji
- Subjects
Physics ,Nuclear and High Energy Physics ,Thallium halides ,Physics::Instrumentation and Detectors ,business.industry ,Halide ,Atmospheric temperature range ,Particle detector ,Semiconductor detector ,chemistry.chemical_compound ,Nuclear magnetic resonance ,chemistry ,Electrode ,Measuring instrument ,Optoelectronics ,High Energy Physics::Experiment ,Polarization (electrochemistry) ,business ,Instrumentation - Abstract
No polarization phenomena were observed in TlBr detectors at room temperature for 30 h by applying Tl electrodes to the detectors.
- Published
- 2008
28. Energy-discrimination x-ray computed tomography system utilizing a scanning cadmium-telluride detector
- Author
-
Akira Ogawa, Manabu Watanabe, Jun Onagawa, Kiyomi Takahashi, Shigehiro Sato, Eiichi Sato, Keitaro Hitomi, Ablajan Abduraxit, and Toshiyuki Enomoto
- Subjects
Physics ,medicine.medical_specialty ,Photon ,business.industry ,Amplifier ,Detector ,Photon energy ,Cadmium telluride photovoltaics ,Intensity (physics) ,Optics ,medicine ,Medical physics ,Tomography ,business ,Energy (signal processing) - Abstract
An energy-discrimination K-edge x-ray computed tomography (CT) system is useful for controlling the image contrast of a target region by selecting both the photon energy and the energy width. The CT system has an oscillation-type linear cadmium telluride (CdTe) detectror. CT is performed by repeated linear scans and rotations of an object. Penetrating x-ray photons from the object are detected by a CdTe detector, and event signals of x-ray photons are produced using charge-sensitive and shaping amplifiers. Both photon energy and energy width are selected out using a multichannel analyzer, and the number of photons is counted by a counter card. In energy-discrimination CT, the tube voltage and tube current were 80 kV and 20 μA, respectively, and the x-ray intensity was 1.92 μGy/s at a distance of 1.0 m from the source and a tube voltage of 80 kV. The energy-discrimination CT was carried out by selecting x-ray photon energies.
- Published
- 2010
29. X-ray detection characteristics of thallium bromide nuclear radiation detectors
- Author
-
R. Hirabuki, Keitaro Hitomi, Tadayoshi Shoji, O. Muroi, Y. Hiratate, and M. Matsumoto
- Subjects
Physics ,Nuclear and High Energy Physics ,Scanner ,Physics::Instrumentation and Detectors ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Detector ,X-ray ,X-ray detector ,chemistry.chemical_element ,Imaging phantom ,Full width at half maximum ,Optics ,Semiconductor ,Nuclear Energy and Engineering ,chemistry ,Thallium ,High Energy Physics::Experiment ,Electrical and Electronic Engineering ,business - Abstract
Semiconductor X-ray detectors have been fabricated from high purity TlBr crystals grown by the traveling molten zone method. X-ray detection characteristics of the TlBr detectors in the individual quantum pulse mode as well as in the current mode have been studied. An energy resolution of 2.5 keV FWHM has been recorded for 22 keV X-rays with a TlBr detector operated in the individual quantum pulse mode at room temperature. The TlBr detectors in the current mode have been tested as flux detectors for an X-ray CT scanner system of a first generation type. The performance of the system has been tested using a wooden phantom. The X-ray CT system has shown good imaging capabilities.
- Published
- 2000
30. Fabrication of TlBr strip detectors
- Author
-
Keitaro Hitomi, Youhei Kikuchi, Mohammad Nakhostin, Tadayoshi Shoji, and Keizo Ishii
- Subjects
Physics ,Shadow mask ,Full width at half maximum ,Optics ,business.industry ,Electrode ,Optoelectronics ,Wafer ,business ,Particle detector ,Semiconductor detector ,Vacuum evaporation ,Anode - Abstract
TlBr strip detectors with four anode strip electrodes were fabricated in this study. The strip electrodes were formed on TlBr wafers 1 mm thick with a vacuum evaporation process through a shadow mask. Each strip had a width of 0.8 mm and a length of 3.5 mm approximately. The gap between the strips was approximately 0.1 mm. Inter strip resistance more than 1 GΩ was obtained with the process. Energy resolutions of 7.0% and 3.8% FWHM were recorded for 511 keV and 1.33 MeV gamma-rays, respectively, with the TlBr strip detector at room temperature.
- Published
- 2009
31. High-speed photon-counting x-ray computed tomography system utilizing a multipixel photon counter
- Author
-
Keitaro Hitomi, Kiyomi Takahashi, Eiichi Sato, Toshiyuki Enomoto, Manabu Watanabe, Shigehiro Sato, Jun Onagawa, and Akiro Ogawa
- Subjects
Physics ,Photon ,medicine.diagnostic_test ,business.industry ,Physics::Medical Physics ,Detector ,Scintillator ,Photon energy ,Photon counting ,Particle detector ,Optics ,Personal computer ,medicine ,business ,Medical radiography - Abstract
High-speed photon counting is useful for discriminating photon energy and for decreasing absorbed dose for patients in medical radiography, and the counting is usable for constructing an x-ray computed tomography (CT) system. A photon-counting x-ray CT system is of the first generation type and consists of an x-ray generator, a turn table, a translation stage, a two-stage controller, a multipixel photon counter (MPPC) module, a 1.0-mm-thick LSO crystal (scintillator), a counter card (CC), and a personal computer (PC). Tomography is accomplished by repeating the linear scanning and the rotation of an object, and projection curves of the object are obtained by the linear scanning using the detector consisting of a MPPC module and the LSO. The pulses of the event signal from the module are counted by the CC in conjunction with the PC. The lower level of the photon energy is roughly determined by a comparator circuit in the module, and the unit of the level is the photon equivalent (pe). Thus, the average photon energy of the x-ray spectra increases with increasing the lower-level voltage of the comparator. The maximum count rate was approximately 20 Mcps, and energy-discriminated CT was roughly carried out.
- Published
- 2009
32. X-ray computed tomography system using a multipixel photon counter
- Author
-
Seiichiro Nomiya, Eiichi Sato, Jiro Nagao, Akihiro Osawa, Keitaro Hitomi, Hiroshi Matsukiyo, Toshiyuki Enomoto, Akira Ogawa, Manabu Watanabe, Shigehiro Sato, and Purkhet Abderyim
- Subjects
Physics ,Photon ,Optics ,business.industry ,Absorbed dose ,Personal computer ,Tomography ,Photon energy ,Scintillator ,business ,Particle detector ,Photon counting - Abstract
A photon-counting K-edge x-ray Computed Tomography (CT) system is useful for discriminating photon energy and for decreasing absorbed dose for patients. The CT system is of the first generation type and consists of an x-ray generator, a turn table, a translation stage, a two-stage controller, a multipixel photon counter (MPPC) module, a 0.5-mm-thick zinc oxide (ZnO) scintillator, a counter board (CB), and a personal computer (PC). Tomography is accomplished by repeating the translation and rotation of an object. Penetrating x-ray photons from the object are detected by the scintillator in conjunction with the MPPC module, and the event signals are counted by the CB. Without using energy discriminating, photon counting CT was carried out by controlling x-ray spectra.
- Published
- 2008
33. Energy-discriminating x-ray camera utilizing a cadmium telluride detector
- Author
-
Purkhet Abderyim, Shigehiro Sato, Manabu Watanabe, Eiichi Sato, Akira Ogawa, Jiro Nagao, Toshiyuki Enomoto, Keitaro Hitomi, Toshio Ichimaru, Hiroshi Matsukiyo, Akihiro Osawa, and Seichiro Nomiya
- Subjects
Physics ,medicine.medical_specialty ,Photon ,business.industry ,Radiography ,Detector ,X-ray ,Photon energy ,Particle detector ,Cadmium telluride photovoltaics ,Optics ,medicine ,Medical physics ,Monochromatic color ,business - Abstract
Energy-discriminating x-ray camera is useful for performing monochromatic radiography using polychromatic x-rays. The x-ray camera was developed to carry out K-edge radiography using iodine-based contrast media. In this camera, objects are exposed by a cerium x-ray generator, and penetrating x-rays are detected by a cadmium telluride (CdTe) detector with an amplifier unit. The optimal x-ray photon energy and energy width are selected out using a multichannel analyzer (MCA), and the photon number is counted by a counter board (CB). Radiography was performed by the detector scanning using an x-y stage driven by a two-stage controller, and x-ray images obtained by energy discriminating are shown in a personal-computer (PC) monitor. Cerium K-series characteristic x-rays are absorbed effectively by iodine based contrast media, and iodine K-edge radiography was performed using x-rays with photon energies just beyond K-edge energy 33.2 keV.
- Published
- 2008
34. Energy-discriminating K-edge x-ray computed tomography system
- Author
-
Jiro Nagao, Purkhet Abderyim, Toshiyuki Enomoto, Akihiro Osawa, Toshio Ichimaru, Keitaro Hitomi, Hiroshi Matsukiyo, Seiichiro Nomiya, Eiichi Sato, Manabu Watanabe, Akira Ogawa, and Shigehiro Sato
- Subjects
Physics ,Optics ,Spectrometer ,K-edge ,business.industry ,Amplifier ,Detector ,Personal computer ,Tomography ,Photon energy ,business ,Charge amplifier - Abstract
An energy-discriminating K-edge x-ray Computed Tomography (CT) system is useful for increasing contrast resolution of a target region and for diagnosing cancers utilizing a drug delivery system. The CT system is of the first generation type and consists of an x-ray generator, a turn table, a translation stage, a two-stage controller, a cadmium telluride (CdTe) detector, a charge amplifier, a shaping amplifier, a multi-channel analyzer (MCA), a counter board (CB), and a personal computer (PC). The K-edge CT is accomplished by repeating translation and rotation of an object. Penetrating x-ray spectra from the object are measured by a spectrometer utilizing the CdTe detector, amplifiers, and MCA. Both the photon energy and the energy width are selected by the MCA for discriminating photon energy. Enhanced iodine K-edge x-ray CT was performed by selecting photons with energies just beyond iodine K-edge energy of 33.2 keV.
- Published
- 2008
35. Evaluation of TlBr detectors with Tl electrodes
- Author
-
Yohei Kikuchi, Tadayoshi Shoji, Keitaro Hitomi, and Keizo Ishii
- Subjects
Physics ,business.industry ,Preamplifier ,Integrator ,Amplifier ,Electrode ,Detector ,Optoelectronics ,business ,Spectroscopy ,Particle detector ,Semiconductor detector - Abstract
Long-term stability of TlBr detectors with Tl electrodes was evaluated in this study. Tl/TlBr/Tl detectors were fabricated and tested with a charge sensitive preamplifier and a spectroscopy amplifier and a gated integrator. Significant improvement of energy resolutions was realized by applying the gated integrator to the TlBr detectors. The full-energy peak positions, counts and resolutions for 662 keV gamma-rays from 137 Cs were monitored during the course of measurements (10 days). By changing the polarity of the applied bias voltages every 24 hours, the Tl/TlBr/Tl detectors exhibited stable spectroscopic performance for totally over 240 hours.
- Published
- 2008
36. Evaluation of the multi-pixel photon counters with inorganic scintillators
- Author
-
Tadayoshi Shoji, Keitaro Hitomi, Seiichiro Nomiya, and Eiichi Sato
- Subjects
Physics ,Photomultiplier ,Scintillation ,Photon ,Physics::Instrumentation and Detectors ,business.industry ,Astrophysics::High Energy Astrophysical Phenomena ,Physics::Medical Physics ,Scintillator ,Avalanche photodiode ,Coincidence ,Nuclear physics ,Full width at half maximum ,Optoelectronics ,Quantum efficiency ,business - Abstract
Multi-Pixel Photon Counter (MPPC) is a Hamamatsu's new Si avalanche photodiode. The main features of the MPPC are very high gain (105 to106) and very fast operation. The MPPC offers considerable advantages over widely used photomultiplier tubes (PMT) for scintillation detection, especially due to their high quantum efficiency, low cost, compactness, low operating voltage, mechanical robustness and insensitivity to magnetic fields. One of the most attractive applications of MPPCs is positron emission tomography (PET). In the present study, the MPPCs were coupled to inorganic scintillators including LSO, BGO and YAP in order to evaluate the scintillator/MPPC devices in terms of energy and timing resolutions for PET applications. The scintillation detector consisted of an LSO scintillator (2 mm × 2 mm × 4 mm) coupled to an MPPC exhibited energy resolutions of 196 keV FWHM and 189 keV FWHM for 511 keV and 662 keV gamma-rays, respectively. The MPPC was operated at a bias of 71.4 V and at room temperature. In order to investigate timing properties of the LSO/MPPC device, coincidence timing spectra between a reference scintillation detector which consisted of a BaF2 crystal coupled to a PMT and the LSO/MPPC device were measured with 511 keV positron annihilation gamma-rays from a 22Na source. A coincidence timing resolution of 3.2 ns FWHM was obtained with the LSO/MPPC system.
- Published
- 2007
37. Simple x-ray computed tomography system utilizing a cadmium telluride detector
- Author
-
Akira Ogawa, Etsuro Tanaka, Shigehiro Sato, Keitaro Hitomi, Tadayoshi Shoji, Kazuyoshi Takayama, Toshiaki Kawai, Eiichi Sato, Hideaki Onabe, Toshio Ichimaru, Seiichiro Nomiya, and Takashi Inoue
- Subjects
Physics ,Optics ,business.industry ,Personal computer ,Detector ,Bremsstrahlung ,Tomography ,Photon energy ,business ,Particle detector ,Photon counting ,Cadmium telluride photovoltaics - Abstract
A simple x-ray computed tomography (CT) system utilizing a cadmium telluride detector and its application to enhanced iodine K-edge angiography are described. The CT system is of the first generation type and consists of an x-ray generator, a turn table, a translation unit, a motor drive unit, a cadmium telluride detector, an interface unit for the detector, and a personal computer (PC). Tomography was performed by the repetition of the translation and rotation. Narrow-photon-energy bremsstrahlung x-rays with a peak photon energy of approximately 35 keV is very useful for performing enhanced K-edge angiography because these rays are absorbed effectively by iodine-based contrast media with a K-edge of 33.2 keV. The tube voltage, the tube current, and the aluminum filter thickness were 60 kV, 1.5 mA, and 3.0 mm, respectively. Holes filled with iodine media in phantoms are visible with high contrasts, and the CT system can be applied to photon-counting and fluorescent x-ray CT systems.
- Published
- 2007
38. Evaluation of LGSO scintillators with Si PIN photodiodes
- Author
-
Yasushi Kurata, Naoaki Shimura, Hiroyuki Ishibashi, Tatsuya Usui, Toshiyuki Onodera, Tadayoshi Shoji, and Keitaro Hitomi
- Subjects
Physics ,Silicon ,Physics::Instrumentation and Detectors ,business.industry ,Detector ,chemistry.chemical_element ,Scintillator ,Photodiode ,law.invention ,Full width at half maximum ,Optics ,chemistry ,law ,Optoelectronics ,Irradiation ,business - Abstract
Low-Lu LGSO scintillators (Lu0.4Gd1.6SiO5: 2.0 mol% Ce) were evaluated with Si PIN photodiode. An LGSO scintillator (2 mm times 2 mm times 4 mm) was coupled to a Si PIN photodiode (HAMAMATSU S1337-33BR). Spectroscopic and timing performance of the LGSO/Si PIN detector was investigated at room temperature. The LGSO/Si PIN detector was irradiated with a 22Na source. The energy resolutions of LGSO/Si PIN detector for the 511 keV full-energy peak was measured to be 17.7% (90.7 keV FWHM). The 511 keV peak position was found to correspond to 3793 e- (conversion factor of 7.4 e-/keV). A coincidence timing spectrum was acquired with the LGSO/Si PIN detector and the reference BaF2 detector. The coincidence timing resolution was measured to be 57 ns FWHM.
- Published
- 2007
39. Characteristics of PbI/sub 2/ crystal for use as a gamma-ray detector
- Author
-
Keitaro Hitomi, Tadayoshi Shoji, T. Suehiro, Yukio Hiratate, and T. Tiba
- Subjects
Crystal ,Physics ,Full width at half maximum ,Electrical resistivity and conductivity ,business.industry ,Resolution (electron density) ,Detector ,Analytical chemistry ,Optoelectronics ,Electron ,Photoelectric effect ,business ,Omega - Abstract
We have been studying a /spl gamma/-ray detector which uses a lead iodide PbI/sub 2/ crystal. The detector fabricated from a PbI/sub 2/ crystal grown by 10-pass zone travelling molten zone (TMZ) method. The /spl mu//spl tau/product of this crystal are estimated to be about 1/spl times/10/sup -6/ cm/sup 2//V for electrons and about 6/spl times/10/sup -7/ cm/sup 2//V for holes. The resistivity of the PbI/sub 2/ crystal is estimated to be about 10/sup 12/ /spl Omega/cm. FWHM energy resolution of the detector for a photoelectric peak for the 59.5 keV /spl gamma/-rays is found to be about 5 keV.
- Published
- 2002
40. Energy-Discriminating Gadolinium K-Edge X-ray Computed Tomography System
- Author
-
Toshiyuki Enomoto, Purkhet Abderyim, Eiichi Sato, Etsuro Tanaka, Akihiro Osawa, Keitaro Hitomi, Jiro Nagao, Toshiaki Kawai, Hiroshi Matsukiyo, Jun Onagawa, Akira Ogawa, Hidezo Mori, Manabu Watanabe, Kiyomi Takahashi, Katsuo Aizawa, and Shigehiro Sato
- Subjects
Physics ,medicine.medical_specialty ,Photon ,business.industry ,Contrast resolution ,Detector ,General Engineering ,General Physics and Astronomy ,Photon energy ,Photon counting ,Optics ,K-edge ,Absorbed dose ,medicine ,Medical physics ,Tomography ,business - Abstract
An energy-discriminating K-edge X-ray computed tomography (CT) system is useful for increasing the contrast resolution of a target region utilizing contrast media and for reducing the absorbed dose for patients. The CT system is of the first-generation type of detector using cadmium telluride (CdTe). CT is performed by repeated translations and rotations of an object. Penetrating X-ray photons from the object are detected by a CdTe detector, and event signals of X-ray photons are produced using charge-sensitive and shaping amplifiers. Both photon energy and energy width are selected out using a multichannel analyzer, and the number of photons is counted by a countercard. To perform energy discrimination, a low-dose-rate X-ray generator for photon counting was developed. Its maximum tube voltage and minimum tube current were 110 kV and 1 µA, respectively. In energy-discriminating CT, the tube voltage and tube current were 100 kV and 20 µA, respectively, and the X-ray intensity was 2.98 µGy/s at a distance of 1.0 m from the source and a tube voltage of 100 kV. The demonstration of enhanced gadolinium K-edge X-ray CT was carried out by selecting photons with energies just beyond the gadolinium K-edge energy of 50.3 keV.
- Published
- 2010
41. Response characteristics of the TlBr radiation detector as a function of the detector temperature
- Author
-
Tadayoshi Shoji, Yukio Hiratate, Keitaro Hitomi, and T. Suehiro
- Subjects
Physics ,Full width at half maximum ,business.industry ,Detector ,Electrode ,Optoelectronics ,Particle ,Electron ,Activation energy ,Atomic physics ,business ,Absorption (electromagnetic radiation) ,Particle detector - Abstract
The radiation detectors were fabricated from the TlBr crystals grown by TMZ method and the FWHM and transit time of electrons and holes were measured as a function of the detector temperature. The TlBr radiation detector shows the best response characteristics at about 320 K for holes. At the temperature of 330 K or above, the transit time and FWHM for the /sup 241/Am /spl alpha/-particle peak become worse. On the other hand, in the case of electron, the spectrum becomes worse with increasing the temperature form 150 K to 380 K. In the case, we can deduce an activation energy of about 0.20 eV for holes and about 0.10 for electron from the temperature dependence of the carrier transit time.
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