IEEE 2017 NSS/MIC/RTSD ControlCenter

Online Program Overview Session: R-07

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Posters and Exhibition viewing

   
Shortcut: R-07
Date: Tuesday, October 24, 2017, 14:00
Room: Grand Hall West
Session type: RTSD Session

Contents

Click on a content entry to get a more detailed information.

Poster panel
(face) ID: 372


Poster Number:
R-07-001

Advanced Theoretical Models For Charge Collection in CdTe Radiation Detectors: a comparison based on experimental data (#3221)

M. Sammartini1, M. Gandola1, G. Bertuccio1

1 Politecnico di Milano, Department of Electronics, Information and Bioengineering, Como, Italy

Content

CdTe detectors performances are limited by trapping of carriers in crystal defects. An accurate evaluation of charge transport properties in the detector is essential to characterize the semiconductor quality, the detector technology and to determine the expected resolution of the system. In this paper, we present the comparison among different theoretical models for charge collection applied to the same experimental data. Unlike the classical Hecht law, second order effects such as holes’ contribution, influence of the surface and of localized spatial charge are taken into account. The validity of these models and their limits have been evaluated on the base of experimental data acquired with a Schottky CdTe pixelated detector irradiated with an 241Am source. A typical value of mobility-lifetime product (µτ)e of 2.6 x 10-3 cm2 V-1 has been found for electrons in the bulk. Additionally, we estimated the mobility-lifetime product for holes (µτ)h, whose value hasn’t been updated in literature in the last years. Moreover, surface recombination velocity and shape of the internal electric field are investigated, which allow to assess the quality of the crystal and of the technology.

Keywords: Charge collection efficiency, Semiconductor detectors, Theoretical models, CdTe
Poster panel
(face) ID: 373


Poster Number:
R-07-002

Characterization of CdZnTe and CdMnTe X-Ray and Gamma-Ray Detectors Using Synchrotron Light Source (#3958)

S. U. Egarievwe1, 3, R. B. James2, E. D. Lukosi3, G. S. Camarda4, U. N. Roy4, A. Hossain4, A. B. Bolotnikov4

1 Alabama A&M University, Electrical Engineering and Computer Science, Normal, Alabama, United States of America
2 Savannah River National Laboratory, Science and Technology, Aiken, South Carolina, United States of America
3 University of Tennessee, Nuclear Engineering, Knoxville, Tennessee, United States of America
4 Brookhaven National Laboratory, Nonproliferation and National Security, Upton, New York, United States of America

Content

Cadmium zinc telluride (CdZnTe) and cadmium manganese telluride (CdMnTe) are wide bandgap semiconductor materials that have found applications in the detection of X-rays and gamma-rays at room temperature without cryogenic cooling. CdZnTe has found applications in medical imaging and in the detection of radiological and nuclear threats. CdMnTe has the potential to result in a more homogeneous and detector-grade crystals with lesser defects because the segregation coefficient of Mn in CdTe matrix is much closer to 1.0 compared to that of Zn. The performance of CdZnTe and CdMnTe detectors are often limited by defects associated with tellurium inclusions and grain boundaries. In this paper, we present the characterization of CdZnTe and CdMnTe materials for nuclear radiation detection applications using synchrotron light source. White X-ray diffraction topography was used to study performance-limiting defects. The results are compared to the electrical and spectral properties of the materials.

Keywords: Semiconductor radiation detectors, CdZnTe, CdMnTe, X-ray and gamma ray detectors, Synchrotron light source, White X-ray diffraction topography
Poster panel
(face) ID: 374


Poster Number:
R-07-003

Comparative Studies on Solvent Grown Cd0.9Zn0.1Te Gamma Detectors in Various Single-Polarity Charge Sensing Device Geometries (#4147)

C. Oner1, T. A. Chowdhury1, K. C. Mandal1

1 University of South Carolina, Department of Electrical Eng., Columbia, South Carolina, United States of America

Content

Cd0.9Zn0.1Te single crystals were grown using a low-cost solvent growth method. Several pieces of ~1 cm3 single crystal blocks were cut and isolated from the grown ingot for detector fabrication and characterization. Infra-red transmission images revealed low concentration of Te inclusions and Pockel’s effect measurements showed fairly uniform depth-wise distribution of the electric field. Detectors in various configurations viz., small pixel, virtual Frisch grid, and coplanar grid were fabricated either on the same crystal in turns or in the similar crystal of the same grown ingot. The detectors were characterized using electrical measurements, alpha spectroscopy, and high-energy gamma ray spectroscopy. Current-voltage measurements exhibited very low leakage current of ~5 nA at 1000 V and resistivities of the order of 8.0×1010 Ohm.cm. Electron drift mobilities of the order of 865 cm2/V.s and electron mobility-lifetime products of the order of 6.8×10-3 cm2/V were calculated using alpha spectroscopy. All the detectors exhibited a distinct peak for the 662 keV gamma rays from a 137Cs radiation source. A digital spectrometer and related software for obtaining pulse-height spectra from coplanar grid detectors has been developed using a dual channel digitizer card. The digital spectrometer was also used to employ offline correction schemes to compensate for the charge loss effects. The small pixel and the virtual Frisch grid detector showed similar energy resolution of 2.5 % for 662 keV gamma rays. However, the virtual Frisch grid configuration revealed the best overall performance among all the configurations with a peak-to-Compton ratio of ~2.6.

Keywords: CZT detector, Gamma ray, Solvent growth, Small pixel, Frisch grid, Coplanar grid, Alpha spectroscopy, Drift mobility, Mobility-lifetime product
Poster panel
(face) ID: 375


Poster Number:
R-07-004

Synthesis and Characterization of Amorphous Selenium Alloys for Radiation Detectors (#4148)

T. A. Chowdhury1, C. Oner1, K. C. Mandal1

1 University of South Carolina, Electrical Engineering Department, Columbia, South Carolina, United States of America

Content

Amorphous selenium (a-Se) alloys have been synthesized for room temperature high-energy nuclear radiation detectors applications. The alloy composition has been optimized to ensure good charge transport properties. The synthesis of alloy materials have been carried out using an alloying reactor at the University of South Carolina (USC) and installed in an argon controlled glove box. The synthesis of a-Se (B-10, As, Cl) and a-Se (Li-6, As, Cl) alloys have been carried out by mixing zone-refined Se and isotopically enriched boron powder and lithium foil with previously synthesized Se-As and Se-Cl master alloys. The synthesized alloys have been characterized by x-ray diffraction (XRD), glow discharge mass spectroscopy (GDMS), differential scanning calorimetry (DSC), Fourier transform infra-red spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), current-voltage (I-V) characteristics, capacitance-voltage (C-V) measurements, and thermally stimulated current measurements (TSC). Raman spectroscopy showed that the master alloy samples were in metastable monoclinic Se8 states, in which seven vibrational modes are located at 40, 59, 77, 110, 133, 227 and 251 cm-1. However, a-Se (Cl) master alloy samples are in stable form of trigonal structure of Se8 ring, in which two modes at 142 and 234 cm-1 were found. DSC measurements showed that a-Se (Cl) MS and a-Se (As) MS samples have one melting point, located at ~219.6 oC, whereas a-Se-As (0.52%)-Cl (5ppm) and Se-As (10.2%) – Cl (60 ppm) both possess two melting points, located at 221 and 220.3 oC respectively. Single element a-Se alloy detectors with two blocking contacts (electrons and holes) have been fabricated and tested and the results show promising characteristics for radiation detectors with its high dark resistivity (1012 - 1013 Ω-cm), good charge transport properties, and cost-effective large area scalability. Details of various steps involved for detector fabrication and characterization will be presented.

Keywords: Amorphous selenium, Radiation detectors, Doping, X-ray diffraction, Glow discharge mass spectroscopy, Differential scanning calorimetry, Raman spectroscopy, High resistivity
Poster panel
(face) ID: 376


Poster Number:
R-07-005

Space Charge Formation in CPG CdZnTe Detectors Investigated by Laser Induced Transient Current Technique using Time–Correlated Switched Biasing (#1779)

P. Praus1, E. Belas1, R. Grill1, J. Pipek1, J. Kunc1

1 Charles University, Institute of Physics, Prague 2, Czech Republic

Content

Space charge formation dynamics in CPG CdZnTe detector examined by the time–correlated switched biasing of the cathode in laser–induced transient (L–TCT) electron current waveforms (CWF) measurement is presented. L–TCT experimental setup based on the direct high frequency amplification of the current pulse flowing on the AC coupled collecting anode grid is used. All CWFs are recorded by using the bias of 580 V and intergrid voltage set on 15 V. Polarization effect of the detector results in the internal electric field distortion in case of continuous DC biasing. This negative influence is frequently overcome by applying an appropriately chosen pulsed biasing of the cathode. Comparison of CWF shape recorded for two detectors with different resolution quality for various setting of time delay of the laser pulse after switched on biasing show significant electron transit time lengthening and remarkable CWF shape alterations with increasing the pulse delay interval in case of worse detector. It is probably caused by the internal space charge formation. On the other hand, nearly constant electron transit time and minor leading edge amplitude increase is observed in case of the detector with better resolution. Such L–TCT waveform measurement enables us to characterize the dynamics of internal space charge formation process and to monitor the electric field warping in the detector volume. Theoretical model of the detector internal space charge formation and simulations of the electric field profile using Shockley–Ramo theorem in a two–dimensional approach are discussed in view of obtained experimental results in the paper.

Keywords: CdZnTe, Coplanar Grid Detector, Time of Flight, Current Waveforms, Transient Current Technique, Switched Biasing
Poster panel
(face) ID: 377


Poster Number:
R-07-006

High-speed and fully spectroscopic X-ray Detector for XRD and EDXRF (#2030)

E. Nygard1, N. Malakhov1, T. Taguchi2, T. Nagano3, K. Yamamoto3

1 Enxense AS, Hvalstad, Norway
2 RIGAKU Corporation, X-ray Apparatus Division, Tokyo, Japan
3 Hamamatsu Photonics K.K., Solid State Division, Hamamatsu, Japan

Content

We are describing a novel 2D pixel detector well suited for XRD and EDXRF applications in particular. This detector is fully spectroscopic and yet offers a very high detection-rate, comparable to many photon-counting detectors (which are not fully spectoscopic). This, over 100 kcps per pixel, detection-rate can be upheld for thousands of pixels operating fully independently in parallel. Using a 0.5mm thick silicon sensor with small pixels, 250um x 250um in our exemplary prototype, we have demonstrated a spectral energy-resolution of 250eV FWHM (@ 5.9keV), measured at a sensor temperature of -10C. For XRD usage, this spectral resolution is better by a good margin to what commercially is avalable today. For XRF usage, this spectral resolution is currently not at par with the SDD detectors commercially used, but since the detection-rate capability is significantly better it will be attractive for many high-rate applications such as e.g. mictro-XRF. In addition, we have set the target of obtaining a spectral energy-resolution comparable to that of the SDD detectors in the next version development of this detector.

Keywords: XRF, ED-XRF, micro-XRF, XRD, hybrid-pixel, high-rate, high-spectral-resolution, x-ray detector
Poster panel
(face) ID: 379


Poster Number:
R-07-008

Development of 3-by-3 High Performance CdZnTe Array System Using VAD_UM v2.2 ASIC and Direct-Attachment (#2643)

Y. Zhu1, Z. He1

1 University of Michigan, Nuclear Engineering and Radiologic Sciences, ann arbor, Michigan, United States of America

Content

CdZnTe is a well-known candidate as high-resolution room-temperature spectrometer. After decades of research efforts, the performance of pixellated CdZnTe detectors is approaching the performance of HPGe. This paper describes the effort to build a 3-by-3 CdZnTe array system based on VAD_UM v2.2 ASIC. The CdZnTe crystals have dimensions of 20×20×15 mm3. The ASICs are connected to the detector using direct-attachment technique to minimizeelectronic noise. VAD_UM ASICs are 130-channel digitizer chip, designed to pursue the optimal performance for pixellated semiconductor detectors. VAD_UM v2.2 is the latest version of the family. It offers four dynamic ranges: 700 keV, 3MeV, 7MeV and 9MeV. With direct-attachment technique, 1.5-keV FWHM electronic noise have been achieved with 700-keV dynamic range. With the best detector, 0.34 % FWHM energy resolution for single-pixel events has been demonstrated at 662 keV.

Keywords: CdZnTe, Digital ASIC, VAD_UM ASIC, High Resolution
Poster panel
(face) ID: 380


Poster Number:
R-07-009

Evaluation of TlBr Detectors for Prompt Gamma-Ray Detection for Proton Therapy (#2703)

M. Nogami1, K. Hitomi1, N. Nagano1, T. Onodera2, H. Hosokawa1, T. Higuma1, S. - Y. Kim1, T. Ito1, A. Terakawa1

1 Tohoku University, Sendai, Japan
2 Tohoku Institute of Technology, Sendai, Japan

Content

Determining the beam range during proton radiation therapy can be realized by detecting characteristic prompt gamma rays emitted from the tissues. Gamma-ray detectors with high detection efficiency is indispensable to detect the prompt gamma-rays consisting high energy gamma-rays (2 – 10 Mev). In this study, feasibility study of using thallium bromide (TlBr) detectors for prompt gamma-ray detection was performed toward the development of efficient beam range monitors for proton radiation therapy. TlBr detectors exhibit high detection efficiency because of the high atomic numbers of the constituent atoms (81, 35) and the high density (7.56 g/cm3). In this study, TlBr crystals were grown by the travelling molten zone method using zone-purified materials. A pixelated TlBr detector was fabricated from the grown crystal. The device had a planar cathode and an anode pixel (1.5 mm × 1.5 mm) surrounded by a guard ring. The detector thickness was approximately 4 mm. Experiments on prompt gamma-ray detection was performed using a proton therapy system at Cyclotron and Radioisotope Center (CYRIC), Tohoku University. A water phantom was irradiated with 80-MeV proton beam. The prompt gamma-rays emitted from the water phantom was detected with the TlBr detector with a lead collimator slit. The slit size was 4 mm. The prompt gamma-rays with the energies more than 1 MeV was measured with the TlBr device. By shifting the Bragg peak position using a range shifter install in the proton therapy system, the distribution of the prompt gamma-rays was measured with the TlBr device at room temperature. The measured counts for the prompt gamma-rays were decreased at around the Bragg peak positon. The experimental data was well consistent with simulation results. The experimental results obtained in this study indicated that the beam range during proton radiation therapy can be estimated by the change of gamma-counts obtained from TlBr detectors.

Keywords: Thallium bromide, Proton therapy, Prompt gamma ray
Poster panel
(face) ID: 381


Poster Number:
R-07-010

Direct Charge-to-Digital Converter for Semiconductor Detector (#2834)

K. Takagi1, 2, T. Terao1, A. Koike2, T. Aoki1, 2

1 Graduate School of Science and Technology, Shizuoka University, Hamamatsu, Shizuoka, Japan
2 ANSeeN Inc., iPERC 303, Hamamatsu, Shizuoka, Japan

Content

This paper introduces a novel X- and gamma-ray read-out circuit based on QDC for semiconductor detector. Semiconductor detector works as direct radiation detector, however conventional read-out circuits indirectly convert the charge produced by detector to digital code through voltage. Because of transient response of voltage, indirect conversion causes some characteristic degradation such as ballistic deficit, increasing dead-time and pileup, non-linearity. Additional circuits to compensate them occupy more circuit area.

On the other hand, these issues brought by voltage can be avoided by using QDC ideally. In addition, direct conversion makes read-out circuit smaller, so this circuit is suited to use for pixelated read-out circuit with energy information. A QDC based on 1-bit delta-sigma modulator is used for read-out circuit in this paper because it has an integrator at the front, resets the integrator automatically during conversion and receives input charge without dead-time. The energy resolution and range are designed by value of feedback DAC and number of counter bit of demodulator placed at the output of QDC respectively.

The principal behavior is confirmed by simulation and experimental circuit built by discrete components. As the result of consideration, 4-bit energy resolution is reasonable for practical application with proposed read-out circuit.

Keywords: semiconductor detector, Radiation detector circuit, Charge-to-digital converter
Poster panel
(face) ID: 382


Poster Number:
R-07-011

Doping of CdTe by Indium or Aluminum with Nd:YAG laser (#3897)

J. Nishizawa1, V. A. Gnatyuk2, C. Zelenska2, A. Koike3, T. Aoki1, 4

1 Shizuoka University, Nanovision Technology, Hamamastu, Shizuoka, Japan
2 National Academy of Sciences of Ukraine, Institute of Semiconductor Physics, Kyiv, Ukraine
3 ANSeeN, iPERC, Hamamastu, Shizuoka, Japan
4 Shizuoka University, Research Institute of Electronics, Hamamastu, Shizuoka, Japan

Content

The CdTe detector has good characteristics of direct conversion. However, a large diameter CdTe is very difficult to grow, so a large area CdTe detector should be better achieved by tiling. To prevent this problem, we have developed the p-n diode in the CdTe by laser doping. Laser processing of the CdTe-In semiconductor-metal interface has been studied by irradiation through the CdTe crystal in water using nanosecond pulses with λ = 1064 nm. We could confirm the p-n diode can be formed by direct laser irradiation of CdTe-metal interface and doping of CdTe and its performance as a detector. Moreover, it has been found that the number of irradiation and power of the laser affect condition of the doping.

Keywords: p-n diode, CdTe, doping, laser irradiation
Poster panel
(face) ID: 383


Poster Number:
R-07-012

Development of X-ray detector using optical separation of scintillator (#3956)

K. Tabata1, J. Nishizawa1, A. Koike2, T. Aoki1

1 Shizuoka University, Hamamatsu, Japan
2 ANSeeN Inc., Hamamatsu, Japan

Content

We are developing a scintillator type imaging detector. The spatial resolution of scintillator type imaging detector is not so high because diffusion of luminescence of scintillator in the detector. As a solution to this, the silicon substrate was processed to make many small square holes in a grid pattern by MEMS technique in order to optically separating scintillator. Moreover, the structure of this grid holes are made integral with silicon photodiode array, and these structure are operated as one detector. This grid holes can get optical separation of visible light occurred by X-ray irradiate to the scintillator. Because the aspect ratio of grid holes is large (widths is 90μm × 90μm and depth is 800μm), it is not so easy filling scintillator inside of grid holes. In this paper, the purpose is filling a scintillator such as CsI:Tl inside of the grid holes and evaluations. In this study, the CsI:Tl was filled inside of the grid holes by vacuum evaporation method. We are used X-ray penetration image, optical microscope and spectrometer to evaluating characteristic of luminescence of scintillator and condition of filling scintillator inside of grid holes. As a result, spatial resolutions of the silicon substrate processed grid holes is better than the flat silicon substrate and characteristic luminescence of scintillator was found.

Keywords: scintillator, CsI:Tl, optical separation, X-ray imaging detector
Poster panel
(face) ID: 384


Poster Number:
R-07-013
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3D Compton Imaging based on Changeable Space Reconstruction (#3588)

Y. Liu1, J. Chu2, Y. Li1, Y. Li1

1 Tsinghua University, Department of Engineering Physics, Beijing, Beijing, China
2 University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America

Content

Compton imaging using position sensitive gamma-ray detectors can efficiently reconstruct an image of a gamma-ray source distribution. With far-field approximation, we can get a 2-D image which is actually the directional distribution of the radioactive source. Although the 2-D images are already incredibly useful for finding radioactive sources, sometimes the knowledge of the actual 3-D location of the source is also important, especially for the complicated environment with a lot of objects.

There are several methods and detector configurations to implement the 3-D imaging of sources distribution, the key point is to provide enough parallax in the measurement. In this article, we used a moving detector array to create the parallax for the 3-D localization, a simultaneous localization and mapping (SLAM) system with two optical cameras was mounted on the detector array to provide both the detector location and environmental information. With the location and orientation of the moving detector in 3-D space, many of the back-projected cones with sufficient parallax in relation to the source were established which make it possible to estimate the source distribution in 3-D imaging space.

List-mode maximum likelihood expectation maximization (MLEM) algorithm was used to reconstruct the source distribution. Since the amount of image voxels in 3-D image space is too large for memory usage and iteration operations, a changeable space reconstruction method was proposed.In this method, both amount and size of space voxels could be changed. Environmental information from a SLAM system and information from preliminary images over a sparse space were used to shrink the image space.

Keywords: Compton Imaging, MLEM, Sparse Space Reconstruction
Poster panel
(face) ID: 385


Poster Number:
R-07-014

Post Growth Annealing of MOVPE-Grown Single Crystal CdTe Epilayers on (211) Si Substrates (#1424)

M. Niraula1, K. Yasuda1, J. Ozawa1, T. Yamaguchi1, S. Tsubota1, T. Mori1, Y. Agata1

1 Nagoya Institute of Technology, Graduate School of Engineering, Nagoya, Aichi, Japan

Content

Epitaxially grown thick single crystal CdTe layers on Si substrate are promising for the development of large-area room-temperature X-ray spectroscopic imaging arrays. We have previously reported on the spectroscopic imaging properties of the detectors fabricated in a p-CdTe/n-CdTe/n+-Si heterojunction diode-type structure, where the CdTe thickness was about 100 mm.1 The detector properties strongly depends on the quality of the CdTe layers. Because of the large lattice mismatch and thermal expansion coefficients differences, CdTe layers grown on the Si substrates are usually strained and consist of high density of dislocations. In this study we performed post-growth rapid thermal annealing of CdTe/Si to improve the structural quality of the crystal.

All CdTe crystals investigated were grown typically at 460 oC on (211)Si substrates, and were 3 -5 mm thick. The thickness was chosen to investigate the properties of the crystals around the CdTe/Si interface using X-ray diffraction technique (XRD). The anneal was performed ex-situ in a quartz-tube by covering the CdTe surface with a bulk CdTe crystal in a flowing hydrogen environment. The temperature was varied from 500 to 900 oC, and different anneal time of 10-90 s as well as anneal cycles were investigated. It was observed that DCRC FWHM values of the crystals decreases after annealing at temperatures above 700 oC, indicating improvement in the structural properties. Detail results of annealing effects on the structural properties of the crystals will be presented.

Keywords: X-ray imaging detector, CdTe thick layer, epitaxial growth, thermal anneal
Poster panel
(face) ID: 386


Poster Number:
R-07-015

Carriers Recombination and Space Charge Formation in Detector Grade CdTe Studied by Laser-induced Transient Current Technique, Dual-wavelength Photo-Hall and Photoluminescence Spectroscopy. (#1856)

A. Musiienko1, R. Grill1, P. Moravec1, J. Pekarek1, P. Praus1

1 Charles University, Institute of Physics, Prague 2, Czech Republic

Content

Detector grade n-CdTe was studied in detail by Laser-induced Transient Current Technique (L-TCT), dual wavelength photo-Hall effect spectroscopy (DWPHES) and photoluminescence spectroscopy (PL). In case of L-TCT the profit of the technique was significantly enhanced by the optimization of the setup allowing us the measurement in the dynamical biasing regime where the space charge formation in the detector could be monitored. The DWPHES setup represents an extension of ordinary photo-Hall effect measurement by the steady excitation on an additional wavelength offering the improved specification of the deep levels (DLs) energies and determination of the DLs positions relatively to band edges. Extensive experimental data were simulated by the Shockley-Read-Hall charge dynamic model developed for this purpose and DLs properties were fitted. The method was demonstrated on a single sample distinguished by unusual features and the benefit of the complex approach to the detailed understanding of processes in the sample was proven. Three detected DLs with threshold energies Ec-0.62 eV, Ec-0.72 and Ec-1.1 eV were found and their effect on the detector quality was revealed. Basic DLs properties such as defect concentration and capture cross-sections were deduced and discussed with respect to the detector properties.

Keywords: CdTe, Laser-induced Transient Current Technique, photo-Hall effect, recombination, polarization, charge kinetics model, Shockley-Read-Hall charge dynamic model, L-TCT, photoluminescence, Hall effect
Poster panel
(face) ID: 387


Poster Number:
R-07-016

Electronic Properties of CH3NH3PbBr3 (#2734)

T. Smith1, C. Seal1, J. Tisdale1, M. Ahmadi1, D. Hamm1, B. Hu1, E. D. Lukosi1

1 University of Tennessee, Knoxville, Tennessee, United States of America

Content

This paper discusses the investigation of the electronic properties of methylammonium lead bromide perovskite semiconductors (MAPB). MAPB samples were investigated for their resistivity, bulk carrier type and concentration, trap density, specific trap cross section and energy level, and mobility-trapping time constant as a function of temperature. Current results are presented on MAPB’s development for ionizing radiation detection with respect to its electronic properties.

Keywords: MAPbBr3, CH3NH3PbBr3, perovskite, PICTS, alpha spectroscopy, single crystal, Hall
Poster panel
(face) ID: 388


Poster Number:
R-07-017

In-House Fabricated Si PIN Diode with Al2O3 Anti-Reflection Layer for Radiation Detectors (#1232)

C. G. Kang1, A. H. Park1, H. K. Cha1, J. H. Ha1, N. - H. Lee1, Y. S. Kim1, J. - H. Oh1, J. M. Park1, S. M. Kim1, S. - J. Lee1, H. S. Kim1

1 Korea Atomic Energy Research Institute, Radiation Equipment Research Division, Jeongeup-si, Jeolabul-do, Republic of Korea

Content

The Korea National Radiation Equipment Fab. Center was built and full-scale operation was started from the Sep. of 2016. From material growth (single crystal TlBr, CWO, CdZnTe etc.) to system integration (container inspection system, missile inspection system, medical equipment etc.), Korea National Radiation Equipment Fab. Center can be the herb of radiation equipment research and commercialization. One of focused research area is Si PIN diode for room-temperature semiconductor radiation detectors (RTSDs) and wafer scale CMOS process is possible in the clean room based fabrication facility.

In this presentation, double deep diffused structured Si PIN diode having ALD Al2O3 anti-reflection and passivation layer were fabricated and characterized. Detailed device fabrication process is described at the experimental section and electrical, optical and radiation response characteristics were characterized.

After ALD Al2O3 anti-reflection layer deposition, ~37% of reverse leakage current was reduced at -70V biased state compared with non-anti-reflection layered Si PIN diode. This results are mainly caused by the suppression of the surface leakage current of Si PIN diode by passivation effect adding to self- cleaning effect of ALD process which can scavenging the dangling bond of Si surface. Spectral responsivity was 0.22 A/W to 0.32 A/W at 450nm to 600nm which is comparable to commercial one. Most of 133Ba energy peak was observed but resolution should be enhanced for using low energy direct type Si PIN detector.

In conclusion, ALD Al2O3 anti-reflection layer effectively reduce the surface leakage current and can be applicable to Si PIN based photodiode and direct radiation detector. Fabrication process optimization still progresses for reduced reverse leakage current and enhanced radiative resolution.

Keywords: Si PIN, semiconductor radiation detector, atomic layer deposition, Al2O3, self-cleaning effect
Poster panel
(face) ID: 389


Poster Number:
R-07-018

A study on the performance of TlBr semiconductor radiation detectors as a function of annealing temperature (#1370)

S. H. Lee1, J. - H. Oh1, C. G. Kang1, J. Park1, H. S. Kim1

1 Korea Atomic Energy Research Institute, Advanced Radiation Technology Institute, Jeongeup, Republic of Korea

Content

Semiconductor radiation detectors which can directly absorb and detect high energy radiation photons such as X- or γ-rays without any additional materials (i.e. scintillation materials) are of technological importance in radiation detection applications such as medical and homeland security fields. In this regard, TlBr, with a bandgap of ~2.7 eV, high density of ~7.56 g/cm3, high atomic number of Tl and Br (81 and 35, respectively), and good charge carrier transport properties of ~2 x 10-4 and ~9 x 10-5 cm2/V for electrons and holes, respectively, has been the prime candidate for the above-mentioned purposes. To get the most out of this high-potential materials for fabricating radiation detectors, optimization of the growth process of ingots, surface polishing and subsequent surface treatments and/or post-growth annealing need to be intensively investigated and optimized.

In this presentation, we report the performance of Au/TlBr/Au radiation detectors as a function of TlBr annealing temperature. TlBr crystal ingot (3 inch in diameter) was grown using a low-pressure vertical Bridgman furnace. After mechanical polishing and chemical etching, some of the TlBr samples were annealed in air at 250, or 300 oC for 24 hours, followed by Au electrode depositions on both sides.

It was observed that the slope and dark currents of the I-V curves decrease as annealing temperature increases. For example, the dark currents at a voltage of 100 V were 21.36 nA and 13.83 nA or Au/TlBr(as-fab.)/Au and Au/TlBr(250)/Au, respectively. Also, the energy resolution at 59.5 keV was lowest (18.2 % at a applied bias of 500 V) for Au/TlBr(250)/Au detector.

In conclusion, Substantial improvement in the energy resolution was achieved with the annealing. On the other hand, the specimens without annealing resulted in no spectrometric results. These results demonstrate that proper annealing further improves the material quality of TlBr.

Keywords: TlBr, semiconductor radiation detector, post-growth annealing, energy resolution
Poster panel
(face) ID: 390


Poster Number:
R-07-019

Electrical parameters of Cd(Mn)Te crystals (#2194)

V. M. Sklyarchuk1, P. Fochuk1, Z. Zakharuk1, Y. Nykoniuk1, S. Dremlyuzhenko1, O. Kopach1, O. Sklyarchuk1, A. Bolotnikov2, R. B. James3

1 Chernivtsi National University, Physics, Chernivtsi, Черновицкая обл., Ukraine
2 Brookhaven National Laboratory, NPP, Upton, New York, United States of America
3 Savannah River National Laboratory, Aiken, South Carolina, United States of America

Content

Electro-physics and structural parameters of Cd(Mn)Te crystals, doped by indium, grown by modified Bridgman method and used for the manufacture of detectors of X- and gamma-radiation, were studied. The crystals possessed slightly pronounced n-type conductivity. Using the linear part of I-V characteristics for the In/Cd(Mn)Te/In structure with two ohmic contacts the material resistivity was defined (5*1010 Ohm*cm, 300 K). From measurements of the absorption spectrum the Cd(Mn)Te gap, which is equal to Eg=1.69 eV at 300 K, was defined.

A study of the resistivity temperature dependence and space-charge-limited current for In/Cd(Mn)Te/In structure was performed. The analysis of the results and statistics of electrons and holes in the compensated semiconductor allowed to define the energy position (Ea = 0.84 eV) and the degree of deep level compensation (98%) that determined the dark conductivity.

Also detecting properties of rectifying Ni/Cd(Mn)Te/In barrier structure were investigated. The dark current under reverse voltage of 500 V was equal to 820 pA, and at 1000 V - 3.7 nA (the area of rectifying contact was 0.1 cm2). Detector resolution under irradiation of uncollimated americium source (Am-241) was equal to ~ 10 keV. To improve the detecting properties of Cd(Mn)Te structures it is necessary to obtain the crystals with high resistivity (> 109 Om*cm), but with a lower degree of deep level compensation, which is responsible for the dark conductivity.

Keywords: Cd(Mn)Te crystals, contacts, detectors
Poster panel
(face) ID: 391


Poster Number:
R-07-020

Comparative Study of X- and γ-Ray Detectors with MoOx, TiOx and TiN Schottky Contacts (#2524)

O. L. Maslyanchuk1, M. M. Solovan1, V. V. Brus1, 2, P. D. Maryanchuk1, I. M. Fodchuk1, V. A. Gnatyuk3, T. Aoki4, C. P. Lambropoulos5, K. Potiriadis6

1 Yury Fedkovych Chernivtsi National University, Chernivtsi, Ukraine
2 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Silicon Photovoltaics, Berlin, Germany
3 V.E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
4 Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan
5 Technological Educational Institute of Sterea Ellada, Psahna-Evia, Greece
6 Greek Atomic Energy Commission, Department of Environmental Radioactivity, Athens, Greece

Content

The capabilities of CdTe-based X- and γ-ray detectors are well known and employed in security systems, space astronomy, medicine and other fields. The full charge collection at the absorption of high-energy photons provides the operation of CdTe-based detectors in spectrometric mode. Therefore, in order to avoid trapping of charge carriers in CdTe detectors, a high bias voltage is required. However, a rapid rise of the leakage current with increasing applied bias voltage is often observed. This is the reason that the study of the detectors characteristics and search for new contact materials remains a relevant scientific and technical task. In this paper we present the analysis of electrical and spectrometric properties of the Mo-MoOx/р-CdTe/MoOx-Mo, Ti-TiOx/р-CdTe/MoOx-Mo and Ti-TiN/р-CdTe/MoOx-Mo structures, fabricated by DC magnetron sputtering of the thin films on semi-insulating CdTe crystals, produced by Acrorad Co. Ltd. The optimization of the conditions of the substrate pretreatment and contacts deposition allowed to reduce the dark (leakage) current of the Mo-MoOx/р-CdTe/MoOx-Mo detectors compared to earlier analogs and, consequently, to improve their spectrometric characteristics. Using high-resolution X-ray diffraction topography and scanning electron microscopy the correlation between the concentration of dislocations, deviations from stoichiometry and electrical characteristics of the samples was established. Moreover, in this paper we report on the investigation of TiOx and TiN thin films as potential contact materials for the A(Cd) face of p-type CdTe crystals used for high radiation detectors. It was shown that the developed Mo-MoOx/р-CdTe/MoOx-Mo, Ti-TiOx/р-CdTe/MoOx-Mo and Ti-TiN/р-CdTe/MoOx-Mo structures can be used for practical applications as X- and γ-ray detectors.

This research was supported by the NATO Science for Peace and Security Programme (Project SENERA SfP-984705). V. Brus thanks Alexander-von-Humboldt Foundation for financial support.

Keywords: CdTe, charge transport, radiation detector, Schottky diodes
Poster panel
(face) ID: 392


Poster Number:
R-07-021

Graphene/semi-Insulating CdTe X-Ray and γ-Ray Radiation Detectors (#2546)

V. V. Brus1, 2, O. L. Maslyanchuk2, M. M. Solovan2, P. D. Maryanchuk2, I. M. Fodchuk2, V. A. Gnatyuk3, T. Aoki4

1 Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Institute for Silicon Photovoltaic, Berlin, Germany
2 Yury Fedkovych Chernivtsi National University, Chernivtsi, Ukraine
3 V.E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
4 Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan

Content

Graphene is a promising candidate for applications in the form of the front electrical contact for radiation detectors. An atomically thin layer of graphene would not absorb low energy of X-rays resulting in a wide operation range of semiconductor detectors. The aim of this study is to prepare novel graphene/CdTe radiation detectors, determine the dominant charge transport mechanisms and measure detection properties of the detectors in terms of energy resolution. High quality and large area graphene was grown in a chemical vapor deposition (CVD) process on a copper foil and then transferred onto pre-cleaned commercially available detector-grade (111) oriented CdTe wafers with the area of 5 × 5 mm2 and thickness of 0.5 mm by means of the standard polymer-assisted transfer technique. The resistivity of the CdTe active material is ρ = (1.4-2) ×109 Ohm·cm at room temperature that is close to the resistivity of the intrinsic CdTe ρi = 4 × 109 Ohm·cm, i.e. the semi-insulating CdTe material under investigation can be considered as an almost intrinsic semiconductor. The I-V characteristics of the prepared graphene/CdTe detectors were measured within a wide bias voltage range at different temperatures. The spectral detection characteristics of the fabricated structures were measured using a charge-sensitive amplifier AMPTEK A250 coupled to a multichannel analyzer MCA8000A. The bias voltage and the shaping time were set to 100 V and 1 μs, respectively. This research was supported by the NATO Science for Peace and Security Programme (Project SENERA SfP-984705). V. V. Brus thanks Alexander-von-Humboldt Foundation for financial support.

Keywords: CdTe, Graphene, radiation detectors
Poster panel
(face) ID: 393


Poster Number:
R-07-022

Determination of the Depletion Region Thickness in X/γ-Ray Detectors with a Schottky Contact (#2991)

V. M. Sklyarchuk1, V. A. Gnatyuk2, T. Aoki3

1 Yuriy Fedkovych Chernivtsi National University, Chernivtsi, Ukraine
2 V.E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
3 Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan

Content

The developed technique of determination of the depletion region thickness in X/γ-ray Schottky diode detectors consists of the measurements of the spectra obtained at irradiation of the detectors by radioisotope radiation from both the rectifying contact and Ohmic contact sides and then comparison of voltage dependences of the photopeak heights. Schottky diodes were developed on the base of semi-insulating Cl-compensated p-like CdTe semiconductor single crystals. The Schottky and Ohmic contacts were formed by deposition of Cr and Au electrodes on the opposite faces of (111) oriented CdTe crystals with different thicknesses (0.5 mm, 0.75 mm, 1 mm, and 2 mm) pre-treated by an argon plasma using different regimes (voltage, current and time), respectively. The dark (leakage) currents of the fabricated Cr/CdTe/Au diode structures with a Schottky barrier did not exceed 3.5 nA at voltage of 1000 V (at room temperature) and such diodes could operate under bias voltage up to 1500 V. The spectral characteristics of the fabricated Cr/CdTe/Au diodes were discussed and relationships between the space charge region width, uncompensated impurity concentration and detection efficiency were analyzed. The experimental results were confirmed by the appropriate calculations of the depletion region thickness of the detectors and the optimal thicknesses of CdTe crystals were determined to achieve the best detection efficiency, highest energy resolution and good stability of the spectral and electrical characteristics of the detectors operating under high energy irradiation at room temperature.

This research was partly supported by the NATO Science for Peace and Security Programme (Project SENERA, SfP-984705).

Keywords: CdTe crystals, depletion region, radioisotope spectra, Schottky diode, space-charge region, X/γ-ray detectors
Poster panel
(face) ID: 394


Poster Number:
R-07-023

Enhanced X/γ-Ray Detection Efficiency in CdTe-based Schottky Diode Detectors Operated in a Stacked Mode (#4161)

V. A. Gnatyuk1, K. S. Zelenska2, V. M. Sklyarchuk3, T. Aoki4

1 V.E. Lashkaryov Institute of Semiconductor Physics of the National Academy of Sciences of Ukraine, Kyiv, Ukraine
2 Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
3 Yuriy Fedkovych Chernivtsi National University, Chernivtsi, Ukraine
4 Shizuoka University, Research Institute of Electronics, Hamamatsu, Japan

This work was supported by the NATO Science for Peace and Security Programme (Project SENERA, SfP-984705).

Content

Ni/CdTe/Au Schottky diodes for X/γ-ray detection were fabricated and tested in spectra measurements. Semi-insolating p-like CdTe crystals with the dimensions of and 10×10×0.75 mm3 were etched in bromine-methanol and treated by the ion bombardment assisted technology. Ni and Au contacts were deposited in vacuum. The diodes demonstrated low leakage currents at high bias voltages (I = 2-4 nA at V = 500 V, I = 5-8 nA at V = 1000 V and I = 9-13 nA at V = 1500 V) and energy resolution (FWHM) of 1.5-2%@662keV at the bias voltage of 800 V. In order to increase a detection efficiency in spectra measurements of high energy X/γ-ray radioisotopes, it was proposed to employ 4 Ni/CdTe/Au Schottky diode detectors operated in a stacked mode providing more interaction depth value and, as a result, an increase in the number of counts. Spectral characteristics of 4 stacked Ni/CdTe/Au detectors were studied and compared with characteristics of a single detector. The value of FWHM for the radioisotope spectra taken by 4 stacked detectors increased twice in comparison with FWHM for the spectra taken by a single detector. At the same time, the peaks (662 keV) in the 137Cs spectra, taken by the 4 stacked Ni/CdTe/Au diode detectors in 2 min and by a single Ni/CdTe/Au diode detector in 5 min at the same applied bias voltage of 800 V, were formed with the same number of counts in both the cases. It evidences an increase in the detection efficiency of the detector stack due to an increase in the γ-photon passage path in the CdTe semiconductor wafers. A longer γ-photon passage path and as a result an increase in the number of counts can be achieved also by placing a 137Cs radioisotope source at the lateral side of the Ni/CdTe/Au detector stack.

Keywords: Ni/CdTe/Au Schottky diodes, X/γ-ray detectors, stacked detectors, spectral characteristics
Poster panel
(face) ID: 396


Poster Number:
R-07-025

Optimization of Fabrication Process for Organic Radiation Detector with Ink-Jet Printing Technology (#2271)

E. Takada1, G. Shikida1, M. Nogami1, H. Imai1, T. Chaki1, F. Nishikido2, S. Naka3, H. Okada3

1 National Institute of Technology, Toyama College, Dept. of Electrical and Control Systems Engineering, Toyama, Toyama, Japan
2 National Institutes for Quantum and Radiological Science and Technology, National Institute of Radiological Sciences, Chiba, Chiba, Japan
3 University of Toyama, Toyama, Toyama, Japan

Content

To develop a radiation detector which does not disturb inspection result in Interventional radiography (IVR), the authors have been developing a new radiation detector where organic photodiodes (OPDs) are fabricated directly on plastic scintillator.  In the previous studies, the authors have shown the possibility of fabricating the detector with Ink-Jet printing technology.  In the present study, parameter study in the fabrication process and pixel size etc. has been carried out.    The device structure of bulk hetero junction OPD was plastic scintillator plate (1 mm)/ IZO (100nm)/ PEDOT: PSS (30 nm) / PCBM: P3HT/ Al (70 nm).   For the devices with some pixel sizes, response to white X-rays were measured. It has been shown that the devices fabricated by ink-jet printing technique could produce comparable current with those by spin coating technique. The X-ray induced current from unit sensing area was larger with smaller pixel size.  Also, X-ray induced current was measured for the devices fabricated with different concentrations of the organic materials in the solvent.  The current was not influenced by the concentration in the range of 1 mg/ml to 10 mg/ml.  Further results of optimization will be presented at the conference.

Keywords: Organif Photodiode, Organic Radiation Detector, Ink-Jet Printing, X-ray, Current, Process Optimization
Poster panel
(face) ID: 397


Poster Number:
R-07-026

Beta-ray Detectors Using Oragnic Semiconductors (#2715)

I. Takasu1, S. Taguchi1, M. Kobayashi1, Y. Nomura1, A. Wada1, F. Aiga1, R. Hasegawa1, N. Kume2

1 Toshiba Corporation, Corporate Research & Development Center, Kawasaki, Kanagawa, Japan
2 Toshiba Corporation, Power and Industrial Systems Research and Development Center, Yokohama, Kanagawa, Japan

Content

We examined indirect and direct conversion beta-ray detectors using organic photodiodes whose detection layer consisted of organic semiconductor materials. To improve the detectability of a single beta-particle in both types of detectors, we developed organic photodiodes with high photoelectron conversion efficiency equivalent to that of silicon photodiodes. Noise in the detectors was suppressed by reducing the dark current and electrical capacitance of the organic photodiodes with thick organic semiconductor layers. 90Sr and 60Co beta-particles were detected by the developed indirect and direct conversion detectors, respectively. These results suggest that the organic detectors, which offer the advantages of large area, light weight, and flexibility, can be used for surface contamination monitoring.

Keywords: beta-ray detector, direct conversion, indirect conversion, organic photodiode, organic semiconductor
Poster panel
(face) ID: 398


Poster Number:
R-07-027

The effect of stoichiometry on as-grown bulk LiInSe2 crystals for neutron detectors (#3058)

Y. Xu1, L. Guo1, H. Zheng1, W. Jie2

1 Northwestern Polytechnical University, Key Laboratory of Radiation Detection Materials and Devices, Xi'an, China
2 Northwestern Polytechnical University, State Key Laboratory of Solidification Processing, Xi'an, China

Content

With the shortage of 3He, it has been a significant and urgent task to develop novel neutron detectors to replace 3He gas tube detector. 6LiInSe2 crystal, a member of Ⅰ-Ⅲ-Ⅴ chalcogenide family with the isotope 6Li, is considered as one promising semiconductor for neutron detection due to its high absorption efficiency. However, currently, its deployment is hampered by the inferior charge carrier transport behaviors, which is mostly attributed to the grown-in defects within the material. Among which, the point defects associated with the stoichiometry determine the optical and electrical properties of the resulting 6LiInSe2 crystals grown from a melt.

The aim of this contribution is to engineer the deviation from stoichiometry for 6LiInSe2 crystal via the low temperature synthesis process combined with the Bridgman method. The molar ratio among Li, In and Se was firstly identified by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Upon comparing the optical transmission and photoluminescence (PL) spectra, the effects of the growth conditions (stoichiometry) on the native point defects were discussed. It was suggested that the cation-rich 6LiInSe2 exhibited a superior performance. Further alpha particle responses demonstrated that an electron mobility and lifetime product of 4.2×10-5 cm2V-1 for cation-rich 6LiInSe2 crystal was obtained. Simultaneously, an energy resolution of 26% was achieved for a 2 mm Au/LiInSe2/Au detector under a bias of 1000 V, illuminate by a 5.48 MeV uncollimated 241Am alpha particle source.

This work was supported by the National Natural Science Foundations of China (Nos. U1631116 and 51202197). Project was also supported by the National Key Research and Development Program of China (2016YFE0115200) and the Natural Science Basic Research Plan in Shaanxi Province of China (2016KJXX-09).

Keywords: LiInSe2, Semiconductor, Detector, Crystal growth
Poster panel
(face) ID: 399


Poster Number:
R-07-028

Neutron Scatter Camera Using Two Arrays of Diamond Detectors (#3997)

A. Alghamdi1, E. D. Lukosi1

1 University of Tennessee, Nuclear Engineering Department, Knoxville, Tennessee, United States of America

Content

In this paper, we present on the simulated performance of a diamond-based neutron scatter camera (DNSC) for both source location and spectral reconstruction. The DNSC consists of two 4×4 planes of diamond detectors, each with a 4×4 array of pixels on them. The various parameters were investigated to gauge their effect on the performance of a DNSC, including both uncertainties in energy deposition and timing. The DNSC can accurately localize at least two neutron sources located very close to each other, and can reconstruct the energy spectrum of a 252Cf neutron source to ~250 keV, contingent on chosen performance parameters of each diamond detector in the array. Details of DNSC design, reconstruction techniques, and other current results will be presented.

Keywords: DNSC
Poster panel
(face) ID: 401


Poster Number:
R-07-030

Development of a Prototype Handheld Spectrometer Using Pixelated TlBr and the VAD_UM Digital ASIC (#2081)

S. O'Neal1, Y. Zhu1, C. Leak1, M. Streicher1, Z. He1

1 University of Michigan, Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan, United States of America

Content

Due to its wide band gap (2.68 eV) and high stopping power, thallium bromide (TlBr) is being investigated as a room temperature semiconductor gamma-ray spectrometer. Performance of better than 1% FWHM at 662 keV has been achieved with ~5x5x5 mm3 pixelated TlBr detectors when cooled to -20°C. At room temperature, TlBr devices have suffered poor performance from polarization due to ionic conduction, limiting the development of field deployable detector systems. Recent studies in surface preparation and contact composition have shown promising results in extending the lifetime of TlBr at room temperature, motivating the development of systems to utilize this material. Previous results with large volume (~12x12x5 mm3) TlBr detectors have been limited to large lab bench systems which are difficult to use in practical measurement scenarios. In this work, we present a new handheld TlBr detector system which can be easily transported for use in the field. We also investigate the performance of this system with TlBr compared with a similarly sized CdZnTe detector in energy resolution and detector efficiency.

Keywords: Gamma Spectroscopy, TlBr, Digital ASIC
Poster panel
(face) ID: 402


Poster Number:
R-07-031

Fabrication of Thallium Bromide Spectrometers with Peltier Cooling Devices (#2687)

S. Kubo1, K. Hitomi2, N. Kimura2, M. Nogami2, N. Nagano2, T. Onodera3, S. - Y. Kim2, T. Ito2, T. Nemoto1

1 Clear Pulse Company, Ltd., Tokyo, Japan
2 Tohoku University, Sendai, Japan
3 Tohoku Institute of Technology, Sendai, Japan

Content

Thallium bromide (TlBr) has very high gamma-ray absorption efficiency originating from its high atomic numbers (Tl: 81, Br: 35) and high density (7.56 g/cm3). The photoelectric cross section of TlBr is approximately 21 times higher than that of germanium for 662-keV gamma rays. Thus, TlBr is a promising material for fabrication of gamma-ray detectors. In this study, TlBr gamma- ray spectrometers with Peltier cooling devices were fabricated from the crystals grown by the traveling molten zone method using zone-purified materials. Cooling TlBr detectors realize improvement of the energy resolutions and long-term stability. A capacitive Frisch grid TlBr detector mounted on a Peltier cooling device was tested by irradiating it with a 137Cs gamma-ray source. The size of the detector crystal was approximately 5 mm × 5 mm × 5 mm. The detector exhibited an energy resolution of 2.2% for 662-keV gamma rays at -20ºC with depth correction and rejection. The long-term stability of the detector system was evaluated by measuring 137Cs spectra continually for two months. No significant degradation of the spectral performance was observed from the detector during the test.

Keywords: Thallium bromide, Spectrometer, gamma-ray detector
Poster panel
(face) ID: 403


Poster Number:
R-07-032

Unmanned Aerial Vehicle Equipped with Spectroscopic CdZnTe Detector for Environmental Monitoring and Smart Agriculture (#3207)

A. Zappettini1, M. Bettelli1, J. Aleotti2, S. Caselli2, G. Micconi2, N. Zambelli3, G. Benassi3, D. Calestani1

1 IMEM, CNR, Parma, Italy
2 University of Parma, Department of Engineering and Architecture, Parma, Italy
3 due2lab s.r.l., Parma, Italy

Content

Recently, we developed a haptic teleoperated UAV carrying a CZT-based nuclear radiation sensor for detection of radiating substances in industrial plants. The CZT detector consists actually of 4 drift strip CZT detectors 20x5x5 with good spectroscopic performances (about 2% at 662 keV). The detector, the batteries, and the read out electronics were housed in a box easily integrable on the UAV, with a total weight of about 400 grams.

The UAV showed optimal performances in relevant and operational environments for the localization and identification of nuclear sources.

In this work, we propose the exploitation of this prototype also for smart agriculture. One of the request of precision agriculture is the knowledge of the groundwater content. Background radiation from soil is partially shielded by the water in the soil. Thus, the measurement of background radiation with our UAV on a specific field can be directly linked to the groundwater availability

Keywords: CdZnTe, UAV, Environmental monitoring, Smart agriculture
Poster panel
(face) ID: 404


Poster Number:
R-07-033

Backscatter Radiography As a Non-Destructive Examination Tool For Concrete Structures (#1519)

S. Cui1, J. K. Nimmagadda1, J. E. Baciak1

1 University of Florida, Materials Science and Engineering/Nuclear Engineering Program, Gainesville, Florida, United States of America

Content

Concrete is widely used in different applications like bridges, tunnels, railroad crossties, etc. Assessing the damage and replacing these concrete structures in the early stages is crucial to prevent any catastrophic events. X-ray backscatter imaging has the advantage of being single-sided imaging technique, which can be used for the non-destructive examination of the concrete structures. The x-ray radiography by selective detection and the x-ray fan beam radiography systems at the University of Florida were used for testing and comparison in order to develop an efficient and a high-resolution x-ray backscatter imaging system. GEANT4 was also used to simulate and study the feasibility of a high-speed rotating pencil beam radiography system. The backscatter images of different concrete contrast tools were produced and analyzed in this paper.

Keywords: Non-Destructive Examination, Concrete Structures, Geant4, X-ray Backscatter
Poster panel
(face) ID: 405


Poster Number:
R-07-034

Angular Detection and Shielding Characterization of Simulated 235U Using Time Encoded Imaging and 3D Position Sensitive CdZnTe Detectors (#1604)

D. Goodman1, S. Brown1, Z. He1, J. Chu1

1 University of Michigan, NERS, Ann Arbor, Michigan, United States of America

Content

Gamma-ray sources are often shielded by unknown materials during in field measurements. Emitted photopeak ratios are modulated by energy dependent shielding attenuation while some gamma-rays are forward-angle Compton scattered. Combined, photopeak attenuation and forward-angle Compton scatter information contained in high resolution CdZnTe spectra provide information to estimate unknown shielding thickness and atomic number. However, estimation is complicated when multiple sources, in various shielding configurations, are present due to spectral angular integration. Time encoded imaging (TEI), a temporal alternative to spatial coded aperture, can undo this angular integration for low energy sources to estimate directional spectra and associated directional shielding. Estimated directional shielding and measured spectra can then be used to estimate emitted source intensities. Estimation of emitted intensity is particularly important for uranium where readily attenuated, low energy 235U lines can be used to estimate enrichment and mass. A proof of concept simulation with multiple 235U sources simultaneously in the field of view, in varied shielding configurations, was performed in Geant4. Reasonable estimation of directional source shielding and emitted intensities was seen.

Keywords: Coded aperture, shielding identification, intensity estimation, angular spectral deconvolution, 3D Position sensitive CdZnTe
Poster panel
(face) ID: 406


Poster Number:
R-07-035

Characteristics of Muon Computed Tomography of Used Fuel Casks Using Algebraic ReconstructionCharacteristics of Muon Computed Tomography of Used Fuel Casks Using Algebraic Reconstruction (#2090)

Z. Liu1, S. Chatzidakis2, C. Liao3, H. Haori Yang3, J. P. Hayward1

1 The University of Tennessee, Knoxville, Nuclear Engineering, Knoxville, Tennessee, United States of America
2 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
3 Oregon State University, Nuclear Engineering, Corvallis, Oregon, United States of America

Content

Cosmic ray muons passing through matter lose energy from inelastic collisions with electrons and are deflected from nuclei due to multiple Coulomb scattering (MCS). The recent developments in position sensitive muon detectors that can measure incoming and outgoing trajectories of individual muons indicate that MCS could be an excellent candidate for spent nuclear fuel imaging. The main purpose of this paper is to evaluate tomographic scanning of spent nuclear fuel stored within vertical and horizontal dry storage casks. A quantitative analysis of the characteristics of images obtained with filtered back projection (FBP) and algebraic reconstruction techniques (ART) are presented herein, as such a comparison has not been carried out in the past. The characteristics of muon CT images were investigated for different numbers of views, pixel sizes and whether or not momentum estimation was included. The expected influence of pixel size on the image quality (while momentum is known) varying the pixel sizes from 2 cm to 10 cm was investigated. A quantity of 400,000 muons were used for each view resulting in 20 minutes of measurement time per view. The results demonstrate that missing fuel assemblies can be identified with more than 5 projections which translates to a significant decrease in measurement time compared with a full reconstruction. Further, knowledge of muon momentum significantly improves image resolution. Selection of optimal pixel size is a tradeoff between resolution and computational cost and in our case, it was found to be 5 cm. Finally, it was shown that a missing fuel assembly has a stronger signal than a fully loaded cask.

Keywords: Muon CT, spent nuclear fuel, GEANT4
Poster panel
(face) ID: 407


Poster Number:
R-07-036

Application of industrial CT system based on synchronous triggering method in aero-engine in-situ inspection (#2463)

Y. Xiao1, 2, D. Yu1, 2, Z. Chen1, 2, B. Wang1

1 Tsinghua University, Department of Engineering Physics, Beijing, China
2 Tsinghua University, Key Laboratory of Particle & Radiation Imaging (Tsinghua University), Ministry of Education, China, Beijing, China

Content

Aero engine is the heart of aircraft, and engine blades are the most important parts. They usually work in bad conditions such as high temperature, high pressure, high rotation speed and alternating load. Some tiny defects may cause disastrous consequences. An effective measure to detect the defects timely is nondestructive detection method bases on industrial CT technology. However, this detection method has several disadvantages, for example, complicated control system, high cost and long testing cycle. What’s more? Some defects are not evident during the shutdown period. We hope to get projections of the blades under different views through its self-rotation. A CT prototype based on synchronous triggering system is being built, and performs well.

Keywords: Synchronous triggering system, Aero-engine in-situ inspection
Poster panel
(face) ID: 408


Poster Number:
R-07-037

A Real-Time 3D Compton Imaging System Using Pixelated CdZnTe (#2686)

D. Shy1, Z. He1

1 University of Michigan, Nuclear Engineering and Radiological Science, Ann Arbor, Michigan, United States of America

Content

The ability to image in three dimensions allows for volumetric mapping of radiological material which has applications for monitoring radiological environments or nuclear security operations. It could provide the 3D location and shape of gamma-ray emitting materials such as undeclared or missing nuclear materials and radiological contamination. The current CdZnTe Polaris camera is able to reconstruct radioactive sources via Compton imaging. However, the system is not able to do it in a 3D space because no routine is present to track detector pose. To facilitate the moving detector platform, the Polaris system consisting of 18 pixelated 2x2x1.5 cm3CdZnTe crystals was mounted with two optical webcams to create the SLAM system. The system has identified the location with a standard error of 10%. In addition, it has the capability of maximum depth range of up to 10 meters. This combination of SLAM and the Polaris Compton Camera makes it possible to create 3D radiation images in real time.

Keywords: 3D Imaging, CZT, Computer Vision, SLAM, Pixilated Detector, Compton Imaging
Poster panel
(face) ID: 409


Poster Number:
R-07-038

Feasibility Study of Using Thallium Bromide Detectors for Single Photon Emission Computed Tomography (#2692)

N. Nagano1, K. Hitomi1, T. Onodera2, M. Nogami1, S. - Y. Kim1, T. Ito1, K. Ishii1

1 Tohoku University, Sendai, Japan
2 Tohoku Institute of Technology, Sendai, Japan

Content

Semiconductor detectors offer high energy resolutions and high spatial resolutions which are indispensable for the detectors for single photon emission computed tomography (SPECT). Currently, cadmium zinc telluride-based gamma cameras are used for the SPECT application. However, their high cost and relatively low detection efficiency limits the wide-spread use of the material for semiconductor-based SPECT systems. In this study, feasibility study of using thallium bromide (TlBr) semiconductor detectors for the SPECT applications were performed by fabricating the pixelated detectors and evaluating the energy resolutions. TlBr crystals were grown in this study by the traveling molten zone method using zone-purified materials. A 5.5-mm-thick pixelated thallium bromide (TlBr) detector with Tl electrodes was fabricated from the crystal. The detector had a planar cathode and nine 1 mm × 1 mm pixelated anodes surrounded by a guard ring. The detector performance was characterized at room temperature. The cathode surface was irradiated with a 57Co gamma-ray source. All nine pixels exhibited almost uniform spectroscopic performance. The average energy resolution of around 8% for 122-keV gamma rays was achieved with the TlBr detector.

Keywords: Thallium bromide, SPECT
Poster panel
(face) ID: 410


Poster Number:
R-07-039

A Monte-Carlo Simulation on Fluorescent X-ray Computed Tomography(FXCT) System for Nuclear Fuels (#2789)

A. Jo1, C. Yoon2, S. - W. Gwak4, A. Lee4, W. Lee3

1 Korea University, Department of Bio-convergence Engineering, Seoul, Republic of Korea
2 Korea University, Health Science Research Center, Seoul, Republic of Korea
3 Korea University, School of Health and Environmental Science, Seoul, Republic of Korea
4 Koera Institute of Nuclear Non-proliferation and Control, Policy and Technology Research Division, Daejeon, Republic of Korea

Content

We have studied Fluorescent X-ray Computed Tomography system (FXCT) to verify material information as well as geometric information in various situations. The nuclear fuel is one of the best examples which the FXCT systems can be used for, because it is important to guarantee the homogeneity of uranium alloys for combustion stability. The image of uranium alloys can be obtained without any external radiation sources like X-ray tubes or gamma-ray sources because uranium-235 emits 185 keV photons itself. We obtained the energy spectrum of uranium pellet with HPGe detector to verify the feasibility for detecting molybdenum and gadolinium contained in the uranium pellets. The Monte-Carlo simulation was carried out to obtain the images which show the distribution of materials in the alloys. We modeled a 1.5 cm-diameter uranium pellet and the pinhole collimator which has 2 mm diameter pinhole size and 3535 detector array for the fluorescent X-ray imaging. We obtained 2-dimensional (radiographic) images first and reconstructed tomographic images from the information of the 2-D images. We verified the feasibility for the detection of Mo and Gd with all of obtained images.

Keywords: Non-Destructive Testing, Fluorescent X-ray Computed Tomography, Nuclear Fuels
Poster panel
(face) ID: 411


Poster Number:
R-07-040

Monte Carlo X-Ray Dose Simulation for µCT with Photon-Counting Detectors (#2992)

F. Fischer1, S. Procz1, M. Fiederle1

1 Albert-Ludwigs-Universität Freiburg, FMF - Freiburg Materials Research Center, Freiburg, Baden-Württemberg, Germany

Content

While the number of conventional X-Ray examinations decreases constantly over the last 20 years, the number of CT examinations per year is steadily growing and with it, the average effective dose for X-Ray imaging techniques rises. To decrease the dose per CT-scan, we use the photon-counting detectors Medipix2 and Medipix3 in combination with an iterative reconstruction technique. These detectors allow X-Ray imaging at low kVp with low image noise and high image quality. Depending on the application, the appropriate sensor material can be chosen. Given the detectors hybrid nature, various materials can be utilized, with high Z materials like CdTe, CZT and GaAs being of particular interest, as they offer more effective efficiency depending on the energy of the X-rays. The combination of such a detector with an iterative reconstruction requiring less projections per CT-scan can save a considerable amount of dose. This paper describes a way to simulate the X-Ray dose for scanning protocols in the Medipix-CT setup. A first step in this process is the determination of emitted X-ray spectra at typical energies. Knowledge of the spectrum can then be used for dose simulation. For the modeling of our micro-focus source as well as for the dose simulation, the general purpose Monte Carlo n-particle transport code MCNP6 was used. Spectra for several energies adequate for material analysis were created, considering both Bremsstrahlung and characteristic X-Rays, and compared to IPEM 78 and other available data. Furthermore, a phantom was introduced to the model to simulate the dose during CT acquisition. The spectra created are in good agreement with other reliable data. In comparison to conventional CT-setups, less dose is needed without image quality degrading.

Keywords: Medipix, Monte Carlo Simulation, X-Ray Spectrum, Radiation Dose, Photon-counting detectors, CT
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(face) ID: 412


Poster Number:
R-07-041

Monte Carlo Evaluation of a CZT 3D Spectrometer Suitable for a Hard X- and Soft-Gamma Rays Polarimetry (#3170)

E. Caroli1, G. De Cesare1, R. M. Curado da Silva3, 8, N. Auricchio1, C. Budtz-Jørgensen2, S. Del Sordo5, J. L. Galvèz6, M. Hernanz6, I. Kuvvetli2, P. Laurent4, O. Limousin4, J. M. Maja7, 3, A. Meuris4, M. Moita8, J. B. Stephen1

1 INAF/IASF-Bologna, Bologna, Italy
2 DTU-Space, Kgs. Lyngby, Denmark
3 LIP-Coimbra, Coimbra, Portugal
4 CEA-Saclay, Gif-sur-Yvette, France
5 INAF/IASF-Palermo, Palermo, Italy
6 IEEC-CSIC/UAB, Cerdanyola del Vallès, Spain
7 Universidade da Beira Interior, Covilhã, Portugal
8 Universidade da Coimbra, Coimbra, Portugal

Content

he measurement of the polarization of hard X- and soft gamma-ray emission from cosmic sources is a key observational parameter to improve our understanding of production mechanisms and geometries. High sensitivity in polarimetric measurements is a mandatory requirement for new instrumentations operating in this energy regime. In this perspective, we are studying the concept of a small high-performance spectro-imager optimized for polarimetry between 100 and 600 keV suitable for a stratospheric balloon-borne payload. We propose a detector with 3D spatial resolution based on highly segmented CZT spectrometer units designed to operate simultaneously as a high performance scattering polarimeter and a high performance spectro-imager. This payload can be considered also as a pathfinder for high performance focal plane detectors for new focusing telescope implementing broad band Laue lens. Herein, we report on the results of a Monte Carlo study to optimize the configuration of the detector for polarimetry. In particular, we will present the polarimetric capabilities and sensitivity for different 3D spatial resolution scales (2 and 0.5 mm) and with different detector response models. Furthermore, to assess the reliability of the numerical model, we compare Monte Carlo results with experimental data obtained with a high performance pixel spectrometer.

Keywords: 3D spectro-imager, CZT, Scattering polarimetry, Hard X and soft-gamma rays, Astrophysics, Monte Carlo simulations
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(face) ID: 413


Poster Number:
R-07-042

Recent Advancements in Neutron Imaging with Lithium Indium Diselenide (#3255)

D. Hamm1, E. Herrera1, H. Bilheaux4, J. Preston2, A. Burger3, A. Stowe2, 1, E. D. Lukosi1

1 University of Tennessee-Knoxville, Nuclear Engineering, Knoxville, Tennessee, United States of America
2 CNS-Y12 Nuclear Security Complex, Oak Ridge, Tennessee, United States of America
3 Fisk University, Nashville, Tennessee, United States of America
4 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America

Content

In this paper, we report on the recent developments of lithium indium diselenide (LISe) for neutron imaging. LISe is both a semiconducting and scintillating material, and both have been utilized in neutron imaging systems. In semiconducting mode, LISe has been coupled to the Timepix ASIC, and tests with gadolinium slits have demonstrated a resolution on the order of the 55 µm pitch of the Timepix ASIC. For scintillating LISe, tests on the random surface roughness and backing (i.e., reflective and antireflective) of LISe substrates of various thickness have helped further understand the observed spatial resolution in previous reports. Using an antireflective backing, one scintillating LISe substrate exhibited a spatial resolution of 34 µm, the best yet for a 904 µm thick scintillating LISe substrate.

Keywords: LiInSe2, Neutron Imaging, Neutron Detection, Scintillator, Lithium indium diselenide, Cold Neutrons, Semiconductor, Timepix
Poster panel
(face) ID: 414


Poster Number:
R-07-043

Proof of Concept for X-Ray Backscatter Imaging Tomosynthesis Using Spectral Detection (#3270)

L. M. Rolison1, S. S. Samant2, K. A. Jordan1, J. E. Baciak1

1 University of Florida, Nuclear Engineering Program, Gainesville, Florida, United States of America
2 University of Florida, Department of Radiation Oncology, Gainesville, Florida, United States of America

Content

This paper describes a proof of concept for X-ray backscatter tomosynthesis by utilizing energy discrimination on detectors in an X-ray backscatter imaging system. This technique has useful applications in both medical imaging and non-destructive testing. The system consists of a collimated pencil beam of radiation surrounded by detectors that measure the fluence of backscattered photons coming from the object under investigation. Since X-ray tubes emit a spectra of radiation and the penetration depth of a photon is energy dependent, detectors using energy discrimination will measure signals generated from different depths within the object. The stochastic radiation transport code MCNP6 was used to simulate and test this concept. The simulated backscatter system used a 5 mm pencil beam surrounded by four 5 cm diameter detectors, with the photon spectra modeled after a 150 kVp lead target X-ray tube. The system raster scanned over a phantom made of tissue that had the letters U and F embedded 6 cm and 8 cm deep, respectively. The letter U was made of air while the letter F was made of compact bone. The measured signals were discriminated into two energy groups, one consisting of photons less than 90 keV and the other anything above it. The two resulting images clearly proved the tomosynthesis concept, with the lower energies detected only showing the letter U, while the higher energies showed both the letters U and F. This technique should easily be applicable to industrial materials, though higher interrogation energies are likely needed.

Keywords: Backscatter, Tomosynthesis, Imaging, Simulation
Poster panel
(face) ID: 415


Poster Number:
R-07-044

Maximum-a-Posteriori Cosmic Ray Muon Trajectory Estimation with Energy Loss for Muon Tomography Applications (#3510)

S. Chatzidakis1, Z. Liu2, J. Jarrell1, J. Scaglione1, J. P. Hayward2

1 Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America
2 University of Tennessee, Nuclear Engineering, Knoxville, Tennessee, United States of America

Content

Recent cosmic ray muon tomography applications use detectors that measure position and direction of the individual muons before and after traversing the imaged object. However, low muon flux, difficulty in measuring muon momentum, and arguably, the substandard resolution of the available imaging reconstruction algorithms impede the application of muon tomography to, among others, the non-destructive assessment of nuclear materials stored within sealed, dense containers. These disadvantages can be partially alleviated by estimating the most likely path of the muon and implementing a probability envelope. One assumption would be to use a straight-line path (SLP) defined by the line between the intersection of the entry and exit path lines. Another commonly used assumption is to calculate the point of closest approach (PoCA). This paper explores the use of a fundamentally different and novel maximum-a-posteriori model for estimating the muon trajectory through a material when the incoming and outgoing positions and directions of a muon are known. The algorithm was tested under various scenarios using detailed validated Geant4 simulations. In all cases, the estimated trajectory is in good agreement with the Geant4 simulated muon path. There are cases where the PoCA path is outside the reconstruction boundaries. These trajectories will typically be rejected during reconstruction, reducing the usable muon flux (or imaging efficiency). It was found that 30% of PoCA events are rejected. Using the trajectory estimate, an increase in the useful muons will result in improved resolution and reduced measurement time. Further, the effect of energy loss due to ionization is investigated, and an energy loss relation is derived and validated. Future work will focus on a quantitative comparison between PoCA and maximum-a-posteriori reconstructed images.

Keywords: Muon path, multiple Coulomb scattering, GEANT4
Poster panel
(face) ID: 417


Poster Number:
R-07-046

Orbital Protons’ Radiation Damage Analysis on a CdTe Detection Plane (#3896)

M. P. Páscoa1, 2, J. M. Maia4, 1, N. Auricchio3, R. M. Curado da Silva1, 2, P. Crespo1, 2, M. Moita1, 2, S. Carmo5, F. Alves5, 6, E. Caroli3, S. Ghithan1, 2

1 LIP - Laboratório de Instrumentação e Física Experimental de Partículas, Coimbra, Portugal
2 University of Coimbra, Department of Physics, Coimbra, Portugal
3 INAF/IASF, Sezione di Bologna, Bologna, Italy
4 University of Beira-Interior, Department of Physics, Covilhã, Portugal
5 University of Coimbra, Instituto de Ciências Nucleares Aplicadas à Saúde, Coimbra, Portugal
6 Instituto Politécnico de Coimbra, Coimbra Health School, Coimbra, Portugal

Content

Future high-energy space telescope missions require further analysis of orbital environment induced activation and radiation damage on main instruments. A scientific satellite in a LEO (Low Earth Orbit) is exposed to the charged particles harsh environment, mainly geomagnetically trapped protons (up to ~300 MeV) that interact with instruments materials generating nuclear activation background noise within the instruments’ operational energy range, as well as generating radiation damage in detector material, deteriorating its performance during the mission time-frame. In order to optimize inflight operational performances of future CdTe high-energy telescope detection planes under orbital radiation environment we measured and analyzed the effects generated by protons on different EURORAD CdTe prototypes (10 to 15mm2 and 1 mm thickness). To carry-out this study several sets of measurements were performed under a cyclotron proton beam, in the energy range from 2 MeV to 14 MeV. The total irradiation fluence was of the order of a typical flight mission duration. Radiation damage effects were analysed through leakage current, the mobility-lifetime (μτ) products for electrons and holes and energy resolution degradation analysis as proton dose was increased and post-irradiation measurements were performed. Further energy resolution measurements at regular time intervals were performed in order to study prototype’s performance recovering potential.

Keywords: Radiation damage, orbital protons, CdTe, focal plane, astrophysics