• Journal of Radiation Protection and Research
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• v.37 no.4
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• pp.191-196
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• 2012

A double-scattering type Compton camera which is appropriate to imaging a high-energy gamma source has been developed for nuclear material surveillance at Hanyang University. The double-scattering type Compton camera can provide high imaging resolution; however, it has disadvantage of relatively low imaging sensitivity than existing single-scattering type Compton camera. In this study, we introduce a novel concept of a dual-mode Compton camera which incorporates two different types of Compton camera, i.e., single- and double-scattering type. The dual-mode Compton camera can operate high-resolution mode and high-sensitivity mode in a single system. To maximize its performance, the geometrical configuration was optimized by using Geant4 Monte Carlo simulation toolkit. In terms of imaging sensitivity, high-sensitivity mode had higher sensitivity than high-resolution mode up to 100 times while high imaging resolution of the double-scattering Compton camera was maintained.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.7
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• pp.1501-1509
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• 2011

Current identity management 1.0 model, which is service provider-centric and isolated, has several problems such as low usability, high cost structure, difficulty in privacy protection, and lack of trust infrastructure. Though various SSO-based identity management 2.0 models including Passport/Live ID, Liberty Alliance/SAML, CardSpace, and OpenID have been recently developed in order to overcome those problems, they are not widely accepted in real Internet environment so as to replace the existing identity management 1.0 model. This paper firstly analyzes the widely-known identity 2.0 models in a comparative way, and then presents a perspective on the development direction of identity management 3.0 model for future Internet.

• Journal of Radiation Protection and Research
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• v.10 no.2
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• pp.155-159
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• 1985

In general, dose rates for a monoenergetic gamma emitter uniformly distributed in an infinite cloud have been calulated by using the monoenergetic point-isotorpic source kernel technique. The most serious limitation on use of the kernel technique is subjected to the fact that it estimates the dose only at the surface of body. As a result, an alternative method is presented in which estimates of dose rate for immersion in a radioactive cloud are resulted from the scattered photon spectra incident on the surface of body. The results are in excellent agreement with other's. Work is currently in progress to apply these results to immersion dose problems associated with absorbed dose distribution in the MIRD phatom.

• Nuclear Engineering and Technology
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• v.26 no.4
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• pp.555-561
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• 1994

The program of performing a fast and automatic analysis of gamma ray spectra obtained by a Multi-Channel Analyzer (MCA) is developed for the surveillance of the nuclear fuel integrity. The integrity of the nuclear fuel is confirmed by the measurement of the radiation level of the reactor coolant through the real time monitoring and the periodic sampling analysis. In Yonggwang nuclear power plane 3 and 4, the Process Radiation Monitoring System (PRMS), which is a real time monitoring system, provides a measure of the fuel integrity. Currently, its spectrometer channel can identify only one radionuclide at a time since the signal processing unit of the spectrometer channel is a Single Channel Analyzer (SCA). To improve the PRMS, it is necessary to substitute the MCA for the SCA The program is operated in a real time mode and an on-demand mode, and automatically performed for all procedures. The test results by using the National Bureau of Standards (NBS) mixed standard source are in good agreement with those from Canberra System 100 which is a commercial MCA Consequently, the developed program seems to be employed for automatic monitoring of gamma rays in nuclear power plants.

• Journal of Radiation Protection and Research
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• v.21 no.1
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• pp.41-50
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• 1996

In this study, the theoretical calculation of the air kerma-to-dose equivalent conversion factors was performed with a Monte Carlo N-Particle transport code for the two types of extremity phantom of the ANSI and the KAERI, respectively. Considering the distribution of absorbed dose due to the interaction of homogeneous Parallel broad beam of monoenergetic primary photons in the range between 15keV and 1.5MeV, the air kerma-to-dose equivalent conversion factors based on the kerma approximation were calculated. It is showed that all the theoretical conversion factors of the two types of the extremity phantom for the ANSI and the KAERI agree well with the experimental values of the ANSI N13.32 draft(1995) for each energy within 5.7%, maximum difference ratio, except for 13.6%, difference ratio in the case for the energy of less than 40keV. It is due to uncertainties of experiment occurred in the low X-ray energy range and geometry considered in the MCNP code.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.97-101
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• 2011

Quad band p-HEMT SP6T switch for handset applications was developed. To achieve the low insertion loss and high isolation, trade-off between "On" state and "Off" state was considered by optimization of unit cell. Especially, in case isolation between transmit port and receive port, it was achieved by large capacitors and miniaturization of chip size was achieved by common voltage control and ground using back via process. Designed SP6T switch has size of $950um{\times}100um$ and take into consideration the gate recess error, excellent loss and isolation was confirmed in operating frequency.

• Progress in Medical Physics
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• v.26 no.4
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• pp.215-222
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• 2015

In this work, we performed a proof-of-concept experiment for phase-contrast x-ray imaging (PCXI) based on a single antiscatter grid and a polychromatic x-ray source. We established a table-top setup which consists of a focused-linear grid having a strip density of 200 lines/inch, a microfocus x-ray tube having a focal-spot size of about $5{\mu}m$, and a CMOS-type flat-panel detector having a pixel size of $48{\mu}m$. By using our prototype PCXI system and the Fourier demodulation technique, we successfully obtained attenuation, scattering, and differential phase-contrast images of improved visibility from the raw images of several selected samples at x-ray tube conditions of $90kV_p$ and 0.1 mAs. Further, fusion image (e.g., the attenuation+the scattering) may have an advantage in displaying details of the sample's structures that are not clearly visible in the conventional attenuation image. Our experimental results indicate that single-grid-based approach seems a useful method for PCXI with great simplicity and minimal requirements on the setup alignment.

• Progress in Medical Physics
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• v.21 no.1
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• pp.93-98
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• 2010

The aim of this work was to establish the methodology for event positioning by measuring depth of interaction (DOI) information and to evaluate the system sensitivity and spatial resolution of the new detector for I-125 and Tc-99m imaging. For this purpose, a Monte Carlo simulation tool, DETECT2000 and GATE were used to model the energy deposition and light distribution in the detector and to validate this approach. Our proposed detector module consists of a monolithic CsI(Tl) crystal with dimensions of $50.0{\times}50.0{\times}3.0\;mm^3$. The results of simulation demonstrated that the resolution is less than 1.5 mm for both I-125 and Tc-99m. The main advantage of the proposed detector module is that by using 3 mm thick CsI(Tl) with maximum-likelihood position-estimation (MLPE) method, high resolution I-125 imaging and high sensitivity Tc-99m imaging are possible. In this paper, we proved that our new detector to be a reliable design as a detector for a multi-energy SPECT.

• Progress in Medical Physics
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• v.20 no.2
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• pp.51-61
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• 2009

A Compton camera, which is based on the geometrical interpretation of Compton scattering, is a very promising gamma-ray imaging device considering its several advantages over the conventional gamma-ray imaging devices: high imaging sensitivity, 3-D imaging capability from a fixed position, multi-tracing functionality, and almost no limitation in photon energy. In the present study, a Monte Carlo-based, user-friendly Compton imaging simulator was developed in the form of a graphical user interface (GUI) based on Geant4 and $MATLAB^{TM}$. The simulator was tested against the experimental result of the double-scattering Compton camera, which is under development at Hanyang University in Korea. The imaging resolution of the simulated Compton image well agreed with that of the measured image. The imaging sensitivity of the measured data was 2~3 times higher than that of the simulated data, which is due to the fact that the measured data contains the random coincidence events. The performance of a stacking-structure type Compton camera was evaluated by using the simulator. The result shows that the Compton camera shows its highest performance when it uses 4 layers of scatterer detectors.

• Progress in Medical Physics
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• v.19 no.4
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• pp.291-297
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• 2008

The purpose of this study is to optimize a parallel-hole collimator for small gamma camera having the pixellated crystal array and evaluate the effect of crystal-collimator misalignment on the image quality using a simulation tool GATE (Geant4 Application for Tomographic Emission). The spatial resolution and sensitivity were measured for the various size of hexagonal-hole and matched square-hole collimators with a Tc-99m point source and the uniformity of flood image was estimated as a function of the angle between crystal array and collimator by misalignment. The results showed that the spatial resolution and sensitivity were greatly improved by using the matched collimator and the uniformity was reduced by crystal-collimator misalignment.