Apply the Light Guide to Improve the Light Collection Efficiency of the Gamma Ray Camera Suyeon Hyeon, Jihwan Boo, Seoryeong Park, and Manhee Jeong* Nuclear & Energy Dept., Jeju National University, 102 Jejudaehak-ro, Jeju-si, Jeju-do, 63243 * Corresponding author: mhjeong@jejunu.ac.kr 1. Introduction Coded-aperture-imaging (CAI) systems are being developed for environmental monitoring and nuclear safety. In particular, portable devices can be used effectively in the fields of homeland security and the application of nuclear plants [1]. Cerium doped Gd2Al2Ga3O12(GAGG(Ce)) has a relatively high density (6.63 g/cm 3 ), excellent energy resolution, and high light yield. Silicon photomultiplier (SiPM) operates at a lower voltage than conventional PMT and can be compacted [2]. Therefore, it is considered a better choice to use SiPM when developing the imaging system. In previous work, we obtain optimized scintillator pixel size from the coupling between SiPM in 12 ⅹ 12 pixel form and 12 ⅹ 12 scintillator arrays of varying pixel sizes. Thus, we developed a gamma-ray imaging system based on coupled 12 ⅹ 12-pixel SiPM with GAGG(Ce) scintillator array [3]. However, since the GAGG(Ce) pixel does not exactly match the SiPM sensor, the light generated in the scintillator may be lost to the gap area between the SiPM pixels, and the leaked light may react with the adjacent pixel to cause problems due to optical cross-talk [4]. In this paper, we conducted to apply a light guide to improve light collection efficiency and reduce optical cross-talk between adjacent SiPM pixels. We compared the peak channel (gain), energy spectrum, and image quality based on the application of the light guide. 2. Materials and Methods Table Ⅰ: Main parameter of the components. Scintillator pixel size 4 ⅹ 4 mm 2 Detector pixel size 3 ⅹ 3 mm 2 Detector pixel gap 1.2 mm Mask pixel size 0.42 ⅹ 0.42 cm 2 Mask material Tungsten ( = 19.3g/cm 3) Table Ⅰ is for the main parameter of the components used in this experiment. Figure 1 shows GAGG(Ce) (Epic-Crystal Co. Ltd., China), a light guide (Epic- Crystal Co. Ltd., China), and SiPM (ArrayC-30035-144P, On Semiconductor) used in this study. The light guide collects scintillation photons from crystal pixels [5]. The light guide used in this experiment is shown in Fig. 2 in order to avoid vacancy between the scintillator and pixel of SiPM. Figure 3 shows a comparison of the light loss in terms of the coupling of GAGG(Ce) and SiPM (left) and the application of the light guide (right) to GAGG(Ce) and SiPM combinations. Fig. 1. Image of the GAGG(Ce) (left), light guide(center), and SiPM(right) used in the experiment. Using a 137 Cs source (activity: 16.54 μCi), we compared the variation of peak channel, energy resolution (R), peak-to-valley ratio (PVR), and peak-to- Compton ratio (PCR). Also, peak signal-to-noise ratio (PSNR), normalized mean-square error (NMSE), and structure similarity (SSIM) were also evaluated with reconstructed images obtained under the same conditions to compare the quality of the images. As PSNR value approaches infinity, the NMSE approaches 0, and SSIM value approaches 1, the higher image quality is evaluated. Fig. 2. Light guide side view and parameters. Fig. 3. Comparison of light losses by light guide application. 3. Results Figure 4 shows a 2D-flood histogram obtained by combining GAGG(Ce) and SiPM with a light guide between GAGG and SiPM. Figure 5 shows the 1D-sum profile, which shows a low edge intensity. Because the difference between the GAGG(Ce) and SiPM intervals causes light leakage, reducing the amount of energy accumulated. Comparing Fig. 5 (a) and Fig. 5 (b), it can be confirmed that intensity from both ends is 3.507% higher on average with a light guide applied. Figure 6 compares and displays the energy spectra obtained by the combination of the two sensors mentioned. The energy spectrum is obtained from the sensor incorporating the light guide observed that the peak center channel value Transactions of the Korean Nuclear Society Virtual spring Meeting May 13-14, 2021