Microstrip Transmission-Line Electrodes for Position Sensitive Radiation Detection

Manhee Jeong,Hammig, Mark D. IEEE 2014 IEEE transactions on nuclear science Vol.61 No.6

<P>A serpentine transmission-line in a microstrip configuration is used to enable fine position sensing in semiconductor radiation detectors. Specifically demonstrated with silicon substrates coupled to standard charge-sensitive preamplifiers, a meandering electrode is used to enable lateral position sensing to within an approximately 1 cm length along the electrode. Configured in a rectilinear shape, the lateral resolution is therefore equivalent to the strip pitch, which we have made as small as 4 μm. The position-of-interaction is extracted using either timing or amplitude techniques, both enabled by the slow-wave propagation structure inherent to the standard metal-semiconductor-insulator configuration of the bounding electrodes, the analysis of which is summarized and compared experimentally.</P>

MCNP-polimi simulation for the compressed-sensing based reconstruction in a coded-aperture imaging CAI extended to partially-coded field-of-view

Jeong, Manhee,Kim, Geehyun Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.1

This paper deals with accurate image reconstruction of gamma camera using a coded-aperture mask based on pixel-type CsI(Tl) scintillator coupled with silicon photomultipliers (SiPMs) array. Coded-aperture imaging (CAI) system typically has a smaller effective viewing angle than Compton camera. Thus, if the position of the gamma source to be searched is out of the fully-coded field-of-view (FCFOV) region of the CAI system, artifacts can be generated when the image is reconstructed by using the conventional cross-correlation (CC) method. In this work, we propose an effective method for more accurate reconstruction in CAI considering the source distribution of partially-coded field-of-view (PCFOV) in the reconstruction in attempt to overcome this drawback. We employed an iterative algorithm based on compressed-sensing (CS) and compared the reconstruction quality with that of the CC algorithm. Both algorithms were implemented and performed a systematic Monte Carlo simulation to demonstrate the possiblilty of the proposed method. The reconstructed image qualities were quantitatively evaluated in sense of the root mean square error (RMSE) and the peak signal-to-noise ratio (PSNR). Our simulation results indicate that the proposed method provides more accurate location information of the simulated gamma source than the CC-based method.

Development of hand-held coded-aperture gamma ray imaging system based on GAGG(Ce) scintillator coupled with SiPM array

Jeong, Manhee,Hammig, Mark Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.11

Emerging gamma ray detection applications that utilize neutron-based interrogation result in the prompt emission of high-energy (>2 MeV) gamma-rays. Rapid imaging is enabled by scintillators that possess high density, high atomic number, and excellent energy resolution. In this paper, we evaluate the bright (50,000 photons/MeV) oxide scintillator, cerium-doped Gd₂Al₂Ga₃O₁₂ (GAGG(Ce)). A silicon photomultiplier (SiPM) array is coupled to a GAGG(Ce) scintillator array (12 × 12 pixels) and integrated into a coded-aperture based gamma-ray imaging system. A resistor-based symmetric charge division circuit was used reduce the multiplicity of the analog outputs from 144 to 4. The developed system exhibits 9.1%, 8.3%, and 8.0% FWHM energy resolutions at 511 keV, 662 keV, and 1173.2 keV, respectively. In addition, a pixel-identification resolution of 602 ㎛ FWHM was obtained from the GAGG(Ce) scintillator array.

Radiation hardness characteristics of Si-PIN radiation detectors

Jeong, Manhee,Jo, Woo Jin,Kim, Han Soo,Ha, Jang Ho Elsevier 2015 Nuclear Instruments & Methods in Physics Research. Vol.784 No.-

<P><B>Abstract</B></P> <P>The Korea Atomic Energy Research Institute (KAERI) has fabricated Si-PIN radiation detectors with low leakage current, high resistivity (>11kΩcm) and low capacitance for high-energy physics and X-ray spectroscopy. Floating-zone (FZ) 6-in. diameter N-type silicon wafers, with ⟨111⟩ crystal orientation and 675μm thick, were used in the detector fabrication. The active areas are 3mm×3mm, 5mm×5mm and 10mm×10mm. We used a double deep-diffused structure at the edge of the active area for protection from the surface leakage path. We also compared the electrical performance of the Si-PIN detector with anti-reflective coating (ARC). For a detector with an active area of 3mm×3mm, the leakage current is about 1.9nA and 7.4nA at a 100V reverse bias voltage, and 4.6pF and 4.4pF capacitance for the detector with and without an ARC, respectively. In addition, to compare the energy resolution in terms of radiation hardness, we measured the energy spectra with <SUP>57</SUP>Co and <SUP>133</SUP>Ba before the irradiation. Using developed preamplifiers (KAERI-PA1) that have ultra-low noise and high sensitivity, and a 3mm×3mm Si-PIN radiation detector, we obtained energy resolutions with 122keV of <SUP>57</SUP>Co and 81keV of <SUP>133</SUP>Ba of 0.221keV and 0.261keV, respectively. After 10, 100, 10<SUP>3</SUP>, 10<SUP>4</SUP> and 10<SUP>5</SUP> Gy irradiation, we tested the characteristics of the radiation hardness on the Si-PIN radiation detectors in terms of electrical and energy spectra performance changes. The fabricated Si-PIN radiation detectors are working well under high dose irradiation conditions.</P>

Characteristics of a Planar-type Cd0.9Zn0.1Te Radiation Detector Grown by Using the Low-pressure Bridgman Method

Manhee Jeong,김한수,Young Soo Kim,Jang Ho Ha 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.8

An indium-doped (7 ppm) Cd0.9Zn0.1Te single crystal for use in room-temperature radiationdetectors has been grown using a low-pressure Bridgman (LPB) furnace at the Korea AtomicResearch Institute. The single crystal has a (111) orientation and a high resistivity of 1 × 1012 ·cm. In addition, the mobility-lifetime products of the electrons and hole are 4.2 × 10−4 cm2/Vand 5 × 10−5 cm2/V, respectively. These values are simply derived by using a Hecht and a neuralequation and 5 MeV alpha particles emitted from an 241Am alpha source. To characterize theCd0.9Zn0.1Te grown by using the LPB method, we fabricated planar detectors with volume of 10× 10 × 2.5 mm3 from a 2-inch-diameter Cd0.9Zn0.1Te ingot.

Comparison of gamma ray localization using system matrixes obtained by either MCNP simulations or ray-driven calculations for a coded-aperture imaging system

Jeong, Manhee,Hammig, Mark D. Elsevier 2020 Nuclear instruments & methods in physics research. Vol.954 No.-

<P><B>Abstract</B></P> <P>A coded-aperture system based on a large-area silicon photo-multiplier (SiPM) coupled with inorganic scintillator was developed for the gamma ray localization in the field of nuclear safety and security. Monte Carlo simulations of the performance were conducted to verify its performance. For the coded-aperture imaging (CAI) system, the mask was designed with an 11-rank modified uniformly redundant array (MURA), and the SiPM readout consisted of 12 × 12 pixels. A two-centimeter-thick tungsten mask was used to encode the gamma ray field. The 144 pixels are read-out with a resistor-based charge-division circuit that reduces the readout outputs from 144 to four signals per module, from which the deposited energy and interaction position can be extracted. For image localization, maximum-likelihood expectation maximization (MLEM) and compress-sensing (CS) methods are used with either: (1) a system matrix generated both the Monte-Carlo N-Particle (MCNP) code, or (2) a mathematical system-matrix model utilizing a ray-driven method. In this paper, reconstructed images of gamma ray sources with various positions and activities were simulated and measured with the simulation tools and the physical system in order to compare and evaluate the relative strengths of the two different system matrix formulations. Both system matrixes generated by MCNP and ray-driven methods are effective in localizing isolated point sources; however, there are critical differences when several gamma sources with different strengths are in the field of view. Although the MCNP-based system matrix requires more processing time to generate, its more accurate incorporation of the competing gamma-ray interaction processes results in effective localization of multiple point sources. In contrast, the rapidly produced ray-driven reconstruction matrix demonstrates reduced accuracy in localizing extending distributions due to its simplified treatment of the particle transport, the magnitude of which is quantified in the paper.</P>

Comparison of Usage Cases in Nuclear Industry of Hand-held Gamma-ray Imagers

Manhee Jeong,Jihwan Boo,Seoryeong Park,Suyeon Hyeon 한국방사성폐기물학회 2021 한국방사성폐기물학회 학술논문요약집 Vol.2021 No.11

Development of a Monte Carlo Simulation Code (MCSDI) and Its Test Results for Optimal Design of a Digital Radiographic System Based on CMOS Image Sensor

ManHee Jeong,B.R. Park,B.S. Han,B.S. Lee,H.S. Cho,S. Kim 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.2

We have developed a Monte Carlo simulation code, the so-called Monte Carlo Simulation for Digital Imager (MCSDI), using the Visual C++ programming language for the optimal design of a digital radiographic system. The MCSDI code has emulated a variety of test conditions for X-ray energy distributions (bremsstrahlung and characteristic X-rays) and exposure levels, beam shapes (parallel or cone-shaped), and scintillator types and structures (Gd2O2S : Tb or CsI(Tl), and at or columnar), and a variety of test phantoms. In this paper, we describe the image characteristics of a digital radiographic system based on a CMOS image sensor using the MCSDI code in terms of the contrast-to-noise ratio (CNR), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum eciency (DQE). This code is expected to be useful in designing the optimal components for a digital radiographic system with respect to the detector pixel size, the scintillator type and thickness, the tube voltage, the exposure level, and so on.

Photo-configurable embossed liquid crystal alignment layer with high azimuthal anchoring strength.

Ahn, Dowon,Jeong, Yong-Cheol,Han, Manhee,Cho, Kuk Young,Lee, Seungsup,Park, Jung-Ki Optical Society of America 2012 Optics express Vol.20 No.6

<P>Herein we describe a photo-alignment layer of improved azimuthal anchoring energy comparable to conventional rubbing method. In order to address the inherent low anchoring stability of photo-alignment layer, we applied embossing technique to conventional photosensitive polymer film, based on the cinnamoyl photoreactive groups, to introduce physical micro-groove effect for additional anchoring energy. From this, 2.5 10?4 J/m2 of azimuthal anchoring energy was achieved, which is considered as synergistic effect from both photoinduced chemical interaction and physical microgroove alignment. In this study, we conducted systematic study on change in anchoring energy as a function of both aspect ratio of embossed pattern and UV exposure dose. We also demonstrated fabrication of sophisticated multi-domain structure of LC cells and discussed theoretical interpretation through LC simulation.</P>

Characteristics of fabricated si PIN-type radiation detectors on cooling temperature

Kim, Han Soo,Jeong, Manhee,Kim, Young Soo,Lee, Dong Hun,Cho, Seung Yeon,Ha, Jang Ho Elsevier BV * North-Holland 2015 Nuclear Instruments & Methods in Physics Research. Vol. No.

<P><B>Abstract</B></P> <P>Si PIN photodiode radiation detectors with three different active areas (3×3mm<SUP>2</SUP>, 5×5mm<SUP>2</SUP>, and 10×10mm<SUP>2</SUP>) were designed and fabricated at the Korea Atomic Energy Research Institute (KAERI) for low energy X- and gamma-ray detection. In Si-based semiconductor radiation detectors, one of the noise sources is thermal noise, which degrades their energy resolution performance. In this study, the temperature effects on the energy resolution were investigated using a 3×3mm<SUP>2</SUP> active area PIN photodiode radiation detector using a Thermoelectric Module (TEM) from room temperature to −23°C. Energy resolutions from 25keV auger electrons to 81keV gamma-ray from a Ba-133 calibration source were measured and compared at every 10°C interval. At −23°C, energy resolutions were improved by 15.6% at 25keV, 4.0% at 31keV, and 1.2% at 81keV in comparison with resolutions at room temperature. CsI(Tl)/PIN photodiode radiation detectors were also fabricated for relatively high energy gamma-ray detection. Energy resolutions for Cs-137, Co-60, and Na-22 sources were measured and compared with the spectral responsivity.</P>