Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 Development of Tiled Gamma-ray Detector Circuit using Photodetector Array Kyeyoung Cho a , Young-Jun Jung a , Jungyeol Yeom a , Hakjae Lee b , Hyemi Cha a , Kisung Lee a a School of Biomedical Engineering, Korea University, Seoul 02841, Korea b ARALE Laboratory Co. Ltd., Seoul, Korea * Corresponding author: kisung@korea.ac.kr 1. Introduction The scintillator array consisted of a 32 × 32 array of discrete pixels with each pixel 1.3 mm × 1.3 mm × 5 The developed sub-miniature gamma camera is a mm in size, as shown in Fig. 1(b). The scintillator compact and lightweight device that is easy to use in array was sealed to prevent hygroscopicity. various fields that require miniaturization, such as portable and wearable devices, and drone-based 2.2 Charge division circuit and preamplifier systems. In this study, we developed an extended-type gamma-ray detector circuit by tiling the photodetector Using a charge division circuit based on the used in the sub-miniature gamma camera and symmetric charge division (SCD) method, 256 output suggested the possibility of extending the gamma-ray signals of each pixel of the photodetectors were detector. Through this, we aimed to verify the encoded into 16 X outputs (X1 – X16) and 16 Y performance improvement such as the extension of the outputs (Y1 – Y16), as shown in Fig. 2. Each output detection area and increased sensitivity. In addition, it signal of the encoded charge division circuit was presented the possibility of extension structure of amplified through 32 channels of the preamplifier. various arrays including the square array. We used a charge sensitive preamplifier (CSP) to improve the signal to noise ratio and to match the 2. Methods and Results impedance between the photodetector and the analog circuits thus minimizing the loss of the signal, as In this section some of the techniques used to shown in Fig. 3. The CSP also converts the develop a tiled gamma-ray detector are described. The photocharge, which is proportional to the energy tiled gamma-ray detector is composed of a intensity of the gamma-ray, into a voltage peak signal. photodetector, a scintillator, analog signal processing circuits (charge division circuit, preamplifier, position encoding amplifier, low pass filter, and baseline adjustment circuit), and digital signal processing circuits (analog to digital converter (ADC) and field programmable gate array (FPGA)). 2.1 Photodetector and scintillator The tiled gamma-ray detector was composed of 8 × 8 multi-pixel photon counter (MPPC) sensors. Four MPPC sensors were arranged in a 2 × 2 tile shape and had a detection area with dimensions of 51.6 mm × 51.6 mm, as shown in Fig. 1(a). We used a CsI(Tl) scintillator, which has good light yield, low energy resolution, and low costs with no background radiation. Fig. 2. Designed symmetric charge division (SCD) circuit Fig. 1. Tiled MPPC array (a), and CsI(Tl) scintillator array (b)
Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 The baseline adjustment circuit was applied to adjust the baseline of each signal to the -500 mV level, as shown in Fig. 5. Fig. 3. Designed charge sensitive preamplifier (CSP) circuit 2.3 Position encoding amplifier Fig. 5. Designed filter and baseline adjustment circuit. The purpose of a position encoding amplifier (PEA) 2.5 ADC and FPGA is to encode a voltage signal of 32 channels from CSP circuits into four channel signals (X+, X-, Y+, Y-) Four channel signals (X+, X-, Y+, Y-) were through a summing amplifier, as shown in Fig. 4. To converted into a digital signal through ADC. The digital determine the position of the detected signals, each signals were determined as event data by a peak voltage signal from the CSP was amplified using detection logic circuit programmed in the FPGA. The different R in values of the summing amplifier. Therefore, event data provides gamma-ray energy and position each signal had different amplitudes. The total gain of information. It was packaged and converted to a the amplifier was designed using the R in and R f values UDP/IP packet communication protocol by a Nios II from the summing amplifier. processor. XR1 2.55k CX1 2.6 Experiment environment and Performance Test 0.638k XR2 XR3 2.125k CX2 XR4 0.671k To verify the performance of the tiled gamma-ray 1.821k XR5 detector, a flood image and energy histogram were CX3 XR6 0.708k acquired using an Na-22 standard source for one hour. 1.594k XR7 CX4 A CsI(Tl) crystal array has an energy resolution of XR8 0.750k 12.92% for an energy histogram. Through the flood XR9 1.417k +3.3V CX5 C65 XR10 0 map image, it was verified that the CsI(Tl) pixels were 0.797k 0.1u XR11 1.275k C66 clearly distinguished, as shown in Fig. 6. In addition, it CX6 0 8 XR12 0.850k 10u 3 V+ U3 + was verified through the peak evaluation of the vertical 0 1.159k 1 XR13 OUT EX+ CX7 2 RL1 - axis profile that 29 pixels were distinguished. The 4 XR14 0.911k Rg1 1B 1k AD823an/AD V- 1B XR15 1.063k 5.1k FWHM of profile was 1.075mm, as shown in Fig. 7. C67 CX8 0 0 0.981k XR16 0.1u C68 0 XR17 0.981k CX9 10u -3.3V XR18 1.063k 8 V+ 3 XR19 0.911k U4 + CX10 0 1 EX- OUT XR20 1.159k 2 RL2 - 4 Rg2 1B 1k V- 0.850k AD823an/AD XR21 1B CX11 5.1k XR22 1.275k 0 XR23 0.797k CX12 1.417k XR24 XR25 0.750k CX13 XR26 1.594k 0.708k XR27 CX14 XR28 1.821k XR29 0.671k CX15 2.125k XR30 XR31 0.638k CX16 XR32 2.55kk Fig. 4. Designed position encoding amplifier (PEA) circuit 2.4 Filter and baseline adjustment circuit To remove the high frequency noise, we designed an Fig. 6. Flood map with Na-22 standard source active low pass filter for output signals (X+, X-, Y+, Y- ) of PEA.
Transactions of the Korean Nuclear Society Virtual Spring Meeting July 9-10, 2020 Fig. 7. Profile with Na-22 3. Conclusions In this study, a tiled gamma-ray detector circuit was developed to improve performance such as the extension of the detection area and increasing sensitivity. Additionally, by acquiring and evaluating an image, the possibility of extension was verified. These results suggest the possibility of extended structures of various arrays including square arrays. Based on the results of this study, we will proceed with performance optimization of the developed circuit and conduct a study on the development of tiled gamma-ray detectors applying the extension structure of various arrays. REFERENCES [1] Jung, Young-Jun, et al. "Development of a sub-miniature gamma camera for multimodal imaging system." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2019). [2] D. Olcott, F. Habte, C.S. Levin, A.M. Foudray, Performance characterization of aminiature, high sensitivity gamma ray camera, IEEE Symp. Conf. Rec. Nucl. Sci. 6(2004) 1492 – 1497 [3] Popov, V., et al. "Analog readout system with charge division type output." 2001 IEEE Nuclear Science Symposium Conference Record (Cat. No. 01CH37310). Vol. 4. IEEE, 2001. [4] J. A. Sorenson and M. E. Phelps, Physics in nuclear medicine, Grune & Stratton New York, 1987.
Recommend
More recommend
