ANALISIS VARIASI MATERIAL SINTILATOR DALAM PENGHITUNGAN EFISIENSI DETEKTOR RADIASI MENGGUNAKAN PHITS VERSI 3.35NIM.: 21106020023Andini Faradilla WijayantiauthorScintillation detectors are among the primary instruments for detecting and measuring gamma radiation, with performance that strongly depends on the physical characteristics of the scintillator material employed. This study aims to analyze and compare the detector design, photon track distribution, energy spectrum, energy resolution, and detection efficiency of four scintillator material variations NaI(Tl), CsI(Tl), CeBr₃, and LaBr₃(Ce) using the Particle and Heavy Ion Transport Code System (PHITS), a Monte Carlo-based simulation software. Simulations were performed using a symmetric configuration of two detectors placed face-to-face with a Cs-137 source positioned at the center between them. The source-to-detector surface distance was varied at 1, 2, 3, 4, and 5 cm. Results show that scintillation detectors for all four materials were successfully modeled as two cylindrical volumes measuring 2 × 2 inches; photon track distribution simulations revealed that photon flux decreases with increasing distance in accordance with the inverse square law, with more homogeneous distributions observed in CeBr₃ and LaBr₃(Ce); and the energy spectra exhibited characteristic features of Cs-137 gamma radiation, including the backscatter peak, Compton continuum, Compton edge, and photopeak. The best energy resolution was achieved by the LaBr₃(Ce) detector, followed by CeBr₃, NaI(Tl), and CsI(Tl). Intrinsic efficiency for all four materials ranged from 49% to 57%, while absolute efficiency ranged from 2% to 18%. Among the four detector materials, LaBr₃(Ce) stands out as the most balanced option, offering the best combination of detection efficiency and energy resolution.530 Fisika2026-06-04UIN SUNAN KALIJAGA YOGYAKARTA;FAKULTAS SAINS DAN TEKNOLOGIThesis