• Nuclear Engineering and Technology
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• v.54 no.12
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• pp.4620-4624
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• 2022

Several cadmium zinc telluride (CZT) crystals were fabricated into radiation detectors using methods that included slicing, dicing, lapping, polishing, and chemical etching. A wet passivation with sodium hypochlorite (NaOCl) was then carried out on the Br-etched detectors. The Te-rich layer on the CZT surface was successfully compensated to the Te oxide layer, which was analyzed with X-ray photoelectron spectroscopy data of both a Br-etched crystal and a passivated CZT crystals. We confirmed that passivation with NaOCl improved the transport property by analyzing the mobility-lifetime product and surface recombination velocity. The electrical and spectroscopic properties of large volume detectors were compared before and after passivation, and then the detectors were observed for a month. Both bar and quasi-hemispherical detectors show an enhancement in performance after passivation. Thus, we could identify the effect of NaOCl passivation on large volume CZT detectors.

• Journal of Radiation Protection and Research
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• v.26 no.3
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• pp.275-279
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• 2001

In uranium enrichment plants and nuclear fuel fabrication facilities, exact measurement of fissile isotope enrichment of uranium is required for material accounting in international safeguards inspection as well as process quality control. The purpose of this study was to develop a simple measurement system which can portably be used at nuclear fuel fabrication plants especially dealing with low enriched uranium. For this purpose, a small size CZT (CdZnTe) detector was used, and the detector performance in low uranium gamma/X -rays energy range was investigated by use of various enriched uranium oxide samples. New enrichment measurement technique and analysis method for low enriched uranium oxide, so-called, 'semi-peak ratio technique' was developed. The newly developed method was considered as an alternative technique for the low enrichment and would be useful to account nuclear material in safeguarding activity at nuclear fuel fabrication facility.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.37 no.3
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• pp.63-71
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• 2000

Infrared (IR) detector chip, which detects the IR radiation from all of the objects and converts to image signal, is usually fabricated using hybrid bonding technology with detector away and readout integrated circuit (ROIC). In this study, we designed the readout circuit and simulated its operations. Fabricating readout circuit chips, we measured operation results satisfying its design requirements in 6V supply voltage. After we mount the IR detector chip in the manufactured thermal image system, thermal images were implemented. The obtained thermal images for high and room temperature target objects are sufficiently recognizable. Using the low noise thermal Image system, we expect to obtain thermal images with higher temperature resolution.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1280-1282
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• 1994

The method of passivation for protecting the $Hg_{l-x}Cd_xTe$ surface is important device fabrication process, because the surface components are highly reactive leading to its chemical and electrical instability. Especially, the material of which composition is x=0.2 or 0.3, is narrow bandgap semiconductor and used as detector of infrared radiation. The device performance of narrow bandgap semiconductors are largely governed by the properties of the semiconductor surface. The electro-chemical processing of $Hg_{l-x}Cd_xTe$ allows rigorous control of the surface chemistry and provides an in-situ monitor of surface reaction. So electro-chemical reduction at specific potential can selectively eliminate the undesirable species on the surface and manipulated to reproducibly attain the desired stoichiometry. This method shows to assess the quality or chemically treated $Hg_{l-x}Cd_xTe$ good surface.

• Nuclear Engineering and Technology
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• v.41 no.5
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• pp.723-728
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• 2009

The response property of the CZT detector ($5{\times}5{\times}5\;mm^3$), widely used in photon spectroscopy, was evaluated by considering the charge collection efficiency, which depends on the interaction position of incident radiation, A quantitative analysis of the energy spectra obtained from the CZT detector was also performed to investigate the tail effect at the low energy side of the full energy peak. The collection efficiency of electrons and holes to the two electrodes (i.e., cathode and anode) was calculated from the Hecht equation, and radiation transport analysis was performed by two Monte Carlo codes, Geant4 and MCNPX. The radiation source was assumed to be 59.5 keV gamma rays emitted from a $^{241}Am$ source into the cathode surface of this detector, and the detector was assumed to be biased to 500 V between the two electrodes. Through the comparison of the results between the Geant4 calculation considering the charge collection efficiency and the ideal case from MCNPX, an pronounced difference of 4 keV was found in the full energy peak position. The tail effect at the low energy side of the full energy peak was confirmed to be caused by the collection efficiency of electrons and holes. In more detail, it was shown that the tail height caused by the charge collection efficiency went up to 1000 times the pulse height in the same energy bin at the calculation without considering the charge collection efficiency. It is, therefore, apparent that research considering the charge collection efficiency is necessary in order to properly analyze the characteristics of CZT detectors.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.767-768
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• 2005

• Proceedings of the Optical Society of Korea Conference
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• 1988.06a
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• pp.37-40
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• 1988

보조전극을 사용하여 전기방전을 궤환 조절하여 연속출력 탄산가스 출력을 안정화하였다. 보조전극은 양극과 접지되어 있는 음극사이에서 음그근처에 설치하였으며 레이저 출력을 HgCdTe-detector로 측정하여 레이저 출력의 요동에 따라 보조전극에 인가되는 전압이 변화되도록 하였다. 보조전극을 사용하여 레이저 출력을 안정화시킨 결과 레이저 출력의 요동은 안정화하지 않았을때의 레이저출력 요동의 1/10 이하로 감소하였다.

• Analytical Science and Technology
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• v.35 no.2
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• pp.69-81
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• 2022

The method of measuring and classifying the energy category of neutrons directly using raw data acquired through a CZT detector is not satisfactory, in terms of accuracy and efficiency, because of its poor energy resolution and low measurement efficiency. Moreover, this method of measuring and analyzing the characteristics of low-energy or low-activity gamma-ray sources might be not accurate and efficient in the case of neutrons because of various factors, such as the noise of the CZT detector itself and the influence of environmental radiation. We have therefore developed an efficient method of analyzing radiation characteristics using a neutron and gamma-ray analysis algorithm for the rapid and clear identification of the type, energy, and radioactivity of gamma-ray sources as well as the detection and classification of the energy category (fast or thermal neutrons) of neutron sources, employing raw data acquired through a CZT detector. The neutron analysis algorithm is based on the fact that in the energy-spectrum channel of 558.6 keV emitted in the nuclear reaction ¹¹³Cd + ¹n → ¹¹⁴Cd + in the CZT detector, there is a notable difference in detection information between a CZT detector without a PE modulator and a CZT detector with a PE modulator, but there is no significant difference between the two detectors in other energy-spectrum channels. In addition, the gamma-ray analysis algorithm uses the difference in the detection information of the CZT detector between the unique characteristic energy-spectrum channel of a gamma-ray source and other channels. This efficient method of analyzing radiation characteristics is expected to be useful for the rapid radiation detection and accurate information collection on radiation sources, which are required to minimize radiation damage and manage accidents in national disaster situations, such as large-scale radioactivity leak accidents at nuclear power plants or nuclear material handling facilities.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.1031-1035
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• 2023

Neutron is an indirectly ionizing particle without charge, which is normally measured by detecting reaction products. Neutron detection system based on measuring gadolinium-converted gamma-rays is a good way to monitor the neutron because the representative prompt gamma-rays of gadolinium have low energies (79, 89, 182, and 199 keV). Low energy gamma-rays and their high attenuation coefficient on materials allow the simple design of a detector easier to manufacture. Thus, we designed a cadmium zinc telluride detector to investigate feasibility of simultaneous detection of gamma-rays and neutrons by using the Monte-Carlo simulation, which was divided into two parts; first was gamma-detection part and second was gamma- and neutron-simultaneous detection part. Consequently, we confirmed that simultaneous detection of gamma-rays and neutrons could be feasible and valid, although further research is needed for adoption on real detection.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.2
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• pp.88-93
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• 1994

We fabricated a large-scale photovoltaic device for detecting-3-5$\mu$m IR, by forming of n$^{+}$-p junction in the $Hg_{1-x}Cd_{x}$Te (MCT) layer which was grown by LPE on CdTe substrate. The composition x of the MCT epitaxial layer was 0.295 and the hole concentration was 1.3${\times}10^{13}/cm^{4}$. The n$^{+}$-p junction was formed by B+ implantation at 100 keV with a does 3${\times}10^{11}/cm^{2}. The n$^{+}$ region has a circular shape with 2.68mm diameter. The vacuum-evaporated ZnS with resistivity of 2${\times}10^{4}{\Omega}$cm is used as an insulating layer over the epitaxial layer. ZnS plays the role of the anti-reflection coating transmitting more than 90% of 3~5$\mu$m IR. For ohmic contacts, gole was used for p-MCT and indium was used for n$^{+}$-MCT. The fabrication took 5 photolithographic masks and all the processing temperatures of the MCT wafer were below 90$^{\circ}C$. The R,A of the fabricated devices was 7500${\Omega}cm^{2}$. The carrier lifetime of the devices was estimated 2.5ns. The junction was linearly-graded and the concentration slope was measured to be 1.7${\times}10^{17}/{\mu}m$. the normalized detectivity in 3~5$\mu$m IR was 1${\times}10^{11}cmHz^{12}$/W, which is sufficient for real application.