A: A CMOS image sensor (CIS) with a large area for the high resolution X-ray imaging was designed. The sensor has an active area of 125 × 125 mm 2 comprised with 2304 × 2304 pixels and a pixel size of 55 × 55 µm 2 . First batch samples were fabricated by using an 8 inch silicon CMOS image sensor process with a stitching method. In order to evaluate the performance of the first batch samples, the electro-optical test and the X-ray test after coupling with an image intensifier screen were performed. The primary results showed that the performance of the manufactured sensors was limited by a large stray capacitance from the long path length between the analog multiplexer on the chip and the bank ADC on the data acquisition board. The measured speed and dynamic range were limited up to 12 frame per sec and 55 dB respectively, but other parameters such as the MTF, NNPS and DQE showed a good result as designed. Based on this study, the new X-ray CIS with ∼50 µm pitch and ∼150 cm 2 active area are going to be designed for the high resolution X-ray NDT equipment for semiconductor and PCB inspections etc.
In this paper, we report a preliminary study on the electrical and optical properties of the first P-on-N SiPM prototype developed at KAIST with a collaboration of NNFC. The sensors were fabricated on a 200 mm n-type silicon epitaxial-layer wafer via customized CMOS process at NNFC. Measurements on the reverse current were carried out on a wafer-level with an auto-probing station and breakdown voltage was found as 32.3 V. As for optical characterization, gain, dark count rate, and photon detection efficiency have been measured as a function of bias voltage at room temperature. In particular, we show that the device had a comparable gain of ∼ 106 with respect to conventional PMTs and had a peak sensitivity in blue light regime. Furthermore, we attempt to explain possible causes of some of phenomena seen from the device characterization.
A: For electronic personal dosimeters (EPDs) based on a spectroscopy system, it is necessary to accurately measure the dose in real-time from the gamma energy spectra. The method of spectrum-to-dose conversion is being used instead of the method of count-to-dose conversion. The G(E) function, a typical method of spectrum-to-dose conversion has been applied to various instruments due to its good dose measurement performance and the advantage of real-time measurements. In this manuscript, we present a method to increase the accuracy of G(E) function for the EPD consisting of a 3 × 3 mm 2 PIN diode coupled with a 3 × 3 × 3 mm 3 CsI(Tl) scintillator. The new G(E) function was calculated using the adaptive moment estimation (ADAM) method based on Monte Carlo simulation. The proposed G(E) function is verified by comparison with the least-square method (LSM), which is the conventional method for calculating the G(E) function and with the gradient-descent method (GDM), which is the basis for the ADAM. The relative difference was acquired to compare the converted dose value using each G(E) function by using 241 Am, 57 Co, 22 Na, 137 Cs, 54 Mn and 60 Co radioisotopes. In addition, the energy response to 137 Cs of each G(E) function was obtained. The relative difference of G(E) function according to LSM, GDM, and ADAM was in the range of ±28.54, ±12.59, and ±9.9%, respectively, and the energy response to 137 Cs was 0.71 to 1, 0.87 to 1.02, and 0.9 to 1.03, respectively.
K: Dosimetry concepts and apparatus; Analysis and statistical methods; Data processing methods; Models and simulations 1Corresponding author.
As the pixel pitch of an X-ray detector decreases, the crosstalk and charge-sharing effects become dominant. The decrease in pixel pitch is also directly related to a reduction in input photons per pixel. Thus, the noise of individual pixel increases in both direct and indirect detectors. In photon counting detector, photon energy shift due to charge sharing and blurring in indirect charge integration detector increases greatly. In this study, we propose the detector shift iteration method (DSIM), which improves both image quality and spatial resolution by solving the abovementioned problems. The Modulation Transfer Function (MTF) and Signal-to-Noise Ratio (SNR) are measured to analyze the image quality and spatial resolution, and the improvement in image contrast is analyzed through various object images. The analysis showed sufficient improvement in both the quality and spatial resolution of the DSIM images. In particular, the DSIM images had better quality than those obtained by sensors with the same pixel pitch as virtual pixel pitch.
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