1. Center for Underground Physics, Institute for Basic Science (IBS), Daejeon 34126, South Korea
2. Department of Radiation, Seorabol College, Gyeongju, Gyeongbuk 38063, South Korea
3. Department of Physics, Kyungpook National University, Daegu 41566, South Korea
4. Central Research Institute, Korea Hydro & Nuclear Power Co., Ltd., Daejeon 34101, South Korea
5. IBS School, University of Science and Technology (UST), Daejeon 34113, South Korea