Sang Mook Kang

A self-biased neutron detector based on an SiC semiconductor for a harsh environment

Neutron detector based on radiation-hard semiconductor materials like SiC, diamond and AlN has recently emerged as an attractive device for an in-core reactor neutron flux monitoring, a spent fuel characterization, and a home land security application. For the purpose of field measurement activity, a radiation detector having a low-power consumption, a mechanical stability and a radiation hardness is required. Our research was focused on the development of a radiation-resistive neutron semiconductor detector based on a wide band-gap SiC semiconductor. And also it will be operated at a zero-biased voltage using a strong internal electric field. The charge collection efficiency (CCE) was over 80% when the biased voltage was zero. When the biased voltage was applied above 20V, the charge collection efficiency reached 100%.

Neutron detection with a GEM

Since GEM was introduced, it has been developed in many application areas. We have developed the neutron detector with GEM coated with the converting foil. The neutron efficiency of a foil was calculated with MCNP and TRIM. The neutron efficiency of multi GEM foils was also calculated. The boron compound was coated on the drift plate, and the neutron was measured with a gas chamber installed with GEM. The process of boron-coating on GEM foil, and the stabilization of it has been under way in KAERI.

Property of a CZT Semiconductor Detector for Radionuclide Identification

Compound semiconductors of high Z value material have been studied intensively for X-ray and γ -ray spectroscopy at room temperature. CdZnTe has wide band gap energy as 1.6 eV and can provide high quantum efficiency with reasonably good energy resolution at room temperature. This study is aimed at determining radionuclide analysis ability by measuring energy resolution of CZT detector which will be applied at nuclear material identification purpose. For experiment we used a CZT detector (5 × 5 × 5 mm3) which is manufactured by eV Products. We have performed our measurement at varied temperatures similar to the outdoor environment for the investigation about temperature dependence of energy resolution and peak centroid fluctuation of CZT detector by using gas cooling and Peltier cooling methods. In order to test radionuclide identification we used various radionuclide samples; plutonium, europium and other standard sources. Pulse height spectra were obtained by standard electronics which consists of a preamplifier, a shaping amplifier, and a multi-channel analyzer.

6H-SiC Solid State Detector Development for a Neutron Measurement

A new solid state detector based on 6H-SiC is one of the promising devices in the nuclear industry for high-level radiation applications in a harsh high-temperature environment. SiC is a semi-conductor with a 3.03-eV band gap energy, and known as a radiation-resistance material. SiC detectors were fabricated by using a 6H-SiC wafer. The properties of the 6H-SiC wafer were over a 106 ohm-cm resistivity, a 380 μm thickness, and a (0001)-oriented type. The 6H-SiC detector was prepared by the processes of a dicing, etching, removal of an oxidation layer and a mounting on an alumina substrate. SiC detector was 10×10 mm2 with a 19.6mm2 active area. The circular metal contacts consisted of a Si-face/Ni/Au and a C-face/Ni/Au structure. Thin LiF and B film was coated onto the SiC detector surface for a neutron converter. The electrical current-voltage performances of the detectors were measured by using the Keithley 4200-SCS parameter analyzer with self voltage sources. Neutron responses were measured by using a 252Cf source.

Influence of the Annealing Process for the Metal Contacts of the SiC Semiconductor Radiation Detector

We have studied the radiation response of a prototype SiC radiation detector by using a 6H-SiC wafer. Metal contacts on the surface of the SiC samples were fabricated by using a thermal evaporator in a vacuum condition. Among the SiC samples, several samples were heated by a Rapid Temperature Annealing(RTA) device for 10 minutes at 300°C. The metal contacts on the annealed and non-annealed samples were scanned by using AFM(Atomic Force Microscope) before and after an annealing process. The current-voltage characteristics of the SiC detectors were measured by parameter analyzer and the radiation response was evaluated by 238Pu with 5.5 MeV α-ray at room temperature and a atmospheric pressure. After annealing process, the surface roughness and the current-voltage characteristics decreased. The Schottky barrier heights of non-annealed and annealed SiC samples were determined as 0.638 eV and 0.688 eV, respectively. Also radiation response spectra of the annealed and non-annealed detectors were similar.We have studied the radiation response of a prototype SiC radiation detector by using a 6H-SiC wafer. Metal contacts on the surface of the SiC samples were fabricated by using a thermal evaporator in a vacuum condition. Among the SiC samples, several samples were heated by a Rapid Temperature Annealing(RTA) device for 10 minutes at 300°C. The metal contacts on the annealed and non-annealed samples were scanned by using AFM(Atomic Force Microscope) before and after an annealing process. The current-voltage characteristics of the SiC detectors were measured by parameter analyzer and the radiation response was evaluated by 238Pu with 5.5 MeV α-ray at room temperature and a atmospheric pressure. After annealing process, the surface roughness and the current-voltage characteristics decreased. The Schottky barrier heights of non-annealed and annealed SiC samples were determined as 0.638 eV and 0.688 eV, respectively. Also radiation response spectra of the annealed and non-annealed detectors were similar.

Development of a High Pressure Xe Ionization Chamber for Environmental Radiation Spectroscopy

A High Pressure Xenon ionization chamber is a promising radiation detector for environmental radiation measurement due to its radiation hardness, its physical rigidity, and its capability of operation at a high temperature up to about 170 °C. A cylindrical high pressure xenon ionization chamber, which was configured with a shielding mesh to improve its energy resolution, was designed on the basis of an electron transfer simulation code (EGSnrc) to extract an optimal density of Xe gas and a thickness of the chamber wall. An electron drift simulation code, Garfield, which was coupled with a Maxwell electric filed calculator, was also employed for the electron drift simulations due to the geometry of the shielding mesh. Shielding inefficiency was also calculated. A spherical ionization chamber was also designed and fabricated to monitor environmental radiation. A noble gas system was constructed to create a noble gas with a high purity and to inject the noble gas up to 60 atm. The combination of an oxygen absorbent (Oxisorb), a molecular sieve, and a high temperature getter can minimize the electro-negative impurities, such as the O2 and N2 gas, to below about several ppb levels. Preliminary tests such as leakage currents, saturation currents, and gas leak test were performed. The performance of the two fabricated ionization chambers at a low dose rate was tested by using a conventional shadow technique with a NIST certified 33.52 MBq 226Ra source in the calibration room at KAERI.