Chankyu Kim

Barkhausen noise in ferromagnetic metallic glass Fe40Ni38Mo4B18

The influence of heat treatment on conventional magnetic properties and Barkhausen noise were studied in ferromagnetic amorphous Fe40Ni38Mo4B18 during a half magnetization cycle for both amorphous and crystallized states. The coercivity, Hc, was low in the amorphous specimens and maximum as the crystallization starts, and decreased with further annealing. The differential permeability near to the Hc, μc, was high in the amorphous specimens and minimum at the onset of crystallization, then increased with annealing. The single peak behavior of the Barkhausen noise (BN) envelope was a common feature in both amorphous and crystallized specimens, and the variation of peak height with heat treatment was similar to that of μc. The magnetic anisotropy energy constant, Ku, was lowest when the crystallite started to nucleate in the amorphous specimen, and increased as the crystallite size grows. The difference between ribbon and transverse directions of BN characteristics such as BN energy, peak height of BN envelo...

Development of an environmental radiation analysis research capability in the UAE.

The UAE has started a nuclear energy program with the aim of having its first four units on-line between 2017 and 2020 and it is important that the country has an environmental radiation analysis capability to support this program. Khalifa University is therefore implementing a research laboratory to support both experimental analysis and radionuclide transport modeling in the aquatic and terrestrial environment. This paper outlines the development of this capability as well as the work in progress and planned for the future.

PLASTIC SCINTILLATOR FOR RADIATION DOSIMETRY

Inorganic scintillators, composed of high-atomic-number materials such as the CsI(Tl) scintillator, are commonly used in commercially available a silicon diode and a scintillator embedded indirect-type electronic personal dosimeters because the light yield of the inorganic scintillator is higher than that of an organic scintillator. However, when it comes to tissue-equivalent dose measurements, a plastic scintillator such as polyvinyl toluene (PVT) is a more appropriate material than an inorganic scintillator because of the mass energy absorption coefficient. To verify the difference in the absorbed doses for each scintillator, absorbed doses from the energy spectrum and the calculated absorbed dose were compared. From the results, the absorbed dose of the plastic scintillator was almost the same as that of the tissue for the overall photon energy. However, in the case of CsI, it was similar to that of the tissue only for a photon energy from 500 to 4000 keV. Thus, the values and tendency of the mass energy absorption coefficient of the PVT are much more similar to those of human tissue than those of the CsI.

CALCULATION OF GAMMA SPECTRA IN A PLASTIC SCINTILLATOR FOR ENERGY CALIBRATIONAND DOSE COMPUTATION

Plastic scintillation detectors have practical advantages in the field of dosimetry. Energy calibration of measured gamma spectra is important for dose computation, but it is not simple in the plastic scintillators because of their different characteristics and a finite resolution. In this study, the gamma spectra in a polystyrene scintillator were calculated for the energy calibration and dose computation. Based on the relationship between the energy resolution and estimated energy broadening effect in the calculated spectra, the gamma spectra were simply calculated without many iterations. The calculated spectra were in agreement with the calculation by an existing method and measurements.

Study on the fast signal transfer for large-area X-ray image sensors

A large area X-ray CMOS image sensor (LXCIS) is a well-known imaging device for high speed and resolution. In design and fabrication process, we found several problems in making LXCIS, especially in signal transferring. A 3-transistor active pixel sensor (3T APS) in LXCIS has a long signal line about 16.896 cm as a worst case. This long signal line consists of metal and it has resistance and capacitance about 21.12 kΩ and 71.87 pF each. We have optimized 3T APSs transistors, applied boosting circuit, and designed a low parasitic resistance and capacitance. From our simulation result, we obtained a high speed operation, which ranges from 13.5 frame per second (FPS) to 18.6 FPS in 1536 × 3072 pixel arrays, and a high dynamic range by increasing maximum voltage of pixel output signal.