섬광체와 광-다이오드 센서를 결합한 검출기 특성 연구: Development of photodiode detector coupled with a scintillator for a cargo scanner

by Bo-Bae Kim (MS Candidate)

Wednesday Nov 18, 2015, 2:50 PM → 3:15 PM Asia/Seoul

216-1호Bo-Bae (제1과학관)

The demand for technology development for security devices to check the dangerous materials due to the risk of terrorism and national security purpose has been increased. We aim to develop a cargo scanner using a dual-beam X-ray. We want to use a combination of a scintillator and a photodiode detector module to detect X-ray. The photodiode is commonly used instead of PMT (photomultiplier) because of higher quantum efficiency, smaller size, and lower operational voltage than PMT. The CdWO4 (CWO) crystal is used to be coupled with the photodiode sensor for X-ray scanner due to good detection efficiency and low afterglow optimized to high-speed scanner. The sensor was designed to collect the scintillation light as much as possible with consideration of the fill factor, the size, thickness of anti-reflective coating layer and depth of implantation in the design. The designed sensors were fabricated on 400 um and 500 um-thicknesses of n-type silicon wafer in ETRI (Electronics and Telecommunications Research Institute). To evaluate the properties of CWO crystals, measurements of emission wavelength, light yield, decay time components were performed. In case of the photodiode, electrical characteristics were measured to show quality of the manufactured sensor and several performance tests with commercial electronics were done. The leakage current and capacitance of the photodiode sensor were measured in order to check the diode characteristic and determine an operating voltage as 100 V. The relative quantum efficiency of the photodiode as a function of the wavelength was measured in KRISS (Korea Research Institute of Standards and Science). The signal-to-noise ratios (SNR) of the photodiode sensor with Sr-90 source were obtained to be better than 80. The low-gamma ray energies of 59.5 keV, 81 keV, 122 keV were detected by the photodiode sensor for the energy resolution (Full Width at Half Maximun, FWHM) and SNR. The alpha particle energy of 5.48 MeV was also detected to measure the energy resolution (FWHM). We investigated the signal yields as the ways of combination of the photodiode and scintillator. The energy resolutions (FWHM) of the photodiode detector coupled with the CsI(Tl) crystal using Na-22, Cs-137, Mn-54, Zn-65, Co-60 and Am-241 sources were measured as 18.3%, 13.6%, 9.3%, 7.3%, 8.8%, 7.5% and 23.2%, respectively.

Thesis Advisor: Prof. Hwanbae Park