GEANT4 simulation study of the start counter for the LAMPS experiment at RAON

The start counter is a scintillator detector designed to measure the reference time of the incident beam for the Large Acceptance Multi-Purpose Spectrometer (LAMPS) experiment at the Rare isotope Accelerator complex for ON-line experiments (RAON). The detector is composed of a plane of plastic scintillator and Multi-Pixel Photon Counter (MPPC) arrays attached to both edges of the scintillator. To understand the performance of the start counter, a simulation framework has been developed using the GENAT4 toolkit, which can simulate the generation and propagation of optical photons. Detailed optical properties of the scintillator and MPPCs are implemented in the simulation for a 5.48 MeV \(\alpha\) $\alpha$ beam corresponding to a \(^{241}\) $_{}^{241}$ Am radiation source. In this paper, we will report on the development of the simulation framework and its performance, including its application to the 250 MeV/A \(^{132}\) $_{}^{132}$ Sn beam as a typical rare isotope beam.