Evaluation of a lead-loaded plastic scintillator for next-generation positron emission tomography detectors using Geant4 simulation

Lead-loaded plastic scintillators are promising candidates for next-generation positron emission tomography (PET) detectors owing to their short fluorescence decay times, high machinability and low production cost. However, their γ-ray detection performance has not been fully quantified. This study evaluated the detection efficiency and energy-resolution characteristics of a 5 wt% lead-loaded plastic scintillator (EJ-256) and compared its performance with that of a conventional polyvinyltoluene (PVT) scintillator. Monte Carlo simulations were performed using Geant4. Monoenergetic 511 keV gamma rays (100 000 events) were irradiated onto scintillator blocks with thicknesses varied from 20 mm to 200 mm in 5 mm increments. The resulting absorbed-energy spectra were analysed using ROOT to determine detection efficiency and the simulated full width at half maximum (FWHM) of the 511-keV photopeak. To identify the thickness region at which detection efficiency saturated, a non-parametric Kruskal–Wallis test was conducted to consecutive thickness groups to determine the point beyond which differences were no longer statistically significant ( p > 0.05). EJ-256 exhibited a distinct 511 keV photopeak, whereas PVT showed only a broad Compton continuum. The detection efficiency increased from 0.9% at 20 mm to 2.9% at 200 mm and saturated above approximately 135 mm, consistent with the Kruskal–Wallis analysis. The simulated 511-keV photopeak width remained stable at approximately 10% FWHM across all thicknesses. These results indicate that EJ-256 demonstrates photon-absorption performance comparable to that of conventional inorganic PET scintillators, while offering substantially faster temporal response and reduced fabrication cost. This combination suggests strong potential for application in future time-of-flight PET detector modules.