TOP-Tier Platform in Extreme Rare Isotope Science (TOPTIER)

The TOPTIER (Top-Tier platform In Extreme Rare Isotope science) initiative represents a strategic international collaboration between South Korea’s RAON(Rare isotope Accelerator complex for ON-line experiments) and Japan’s RIBF (Radioactive Isotope Beam Factory), two of the world’s leading rare isotope (RI) beam facilities. Launched in July 2024, TOPTIER aims to establish a sustainable platform for joint research, researcher exchange, and shared infrastructure in the field of nuclear physics. This paper outlines the motivations behind TOPTIER’s creation, its three-stage development roadmap (2024–2033), and major goals including the discovery of extreme neutron-rich isotopes. Notable Korean-led projects approved by RIKEN’s Program Advisory Committee demonstrate the increasing impact of this collaboration. Furthermore, the platform supports global talent cultivation through summer schools, workshops, and postdoctoral programs. By integrating complementary strengths in RI beam production and experimental capabilities, TOPTIER is poised to become a global hub for extreme rare isotope research and to contribute to a deeper understanding of the origin of matter and the universe.