1. Radiation Instrumentation Research Division, Korea Atomic Energy Research Institute, Daejeon 305-353, South Korea
2. School of Electronics Engineering, College of IT Engineering, Kyungpook National University, Daegu, 702-701, South Korea
3. Department of Electronics Engineering, Sejong University, Seoul 143-747, South Korea
4. Department of Electronics Engineering, University of Incheon, Incheon 402-751, South Korea