Development of the segmented plastic scintillation detector GARi for studying $r$-process nucleosynthesis at RIBF

\(\beta\)-decay properties of very neutron-rich nuclei, such as the half-life and the \(\beta\)-delayed neutron emission probabilities, play an essential role in the astrophysical rapid neutron capture process (r-process), where elements heavier than iron may be synthesized. Investigating those crucial properties has been one of the main objectives of the experimental programs at the RIKEN RI Beam Factory (RIBF). Recently, the development of a fast-timing detector system comprising a highly segmented plastic scintillation detector GARi (Gas-cell Active detector for Radioisotope decay), a neutron time-of-flight detector array, and a LaBr\textsubscript{3} detector array is being conducted for the measurement of \(\beta\)-delayed neutron emission and other related \(\beta\)-decay properties of neutron-rich nuclei at the F11 decay station of RIBF. The GARi detector has been constructed from a fast, segmented plastic scintillator coupled with nine multi-anode photomultiplier tubes (PMTs), resulting in enhanced position sensitivity. Therefore, this detector can be employed as an implantation detector and can also serve as a trigger signal in neutron time-of-flight experiments. This work details the development of the GARi detector and the results tested with the radioactive sources.