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Monte Carlo simulations were used to investigate the correlation between luminosity parameters and pulse shape discrimination (PSD) and subsequently compared with experimental results from CsI:Tl. Luminosity intensity parameters Af, As (fast and slow initial luminosities) and temporal luminosity parameters τf, τs (fast and slow decay time constants) of a dual decay mode scintillator were applied to create a dynamic model with Crystal Ball simulation system. The simulated pulses were analyzed with charge comparison (CC) and constant time discrimination (CTD) PSD methods followed by quantification of the histogrammed pulse data with Figure of Merit (FoM) and spillover (pulse misclassification). Performance in terms of FoM and spillover is compared with that of fixed reference pulses set at (Af τf/As τs)γ = 1 and (Af τf/As τs)γ = 0.1. For the CC method, independent of the reference pulse characteristics [(Af τf/As τs)γ = 1 or = 0.1], τs is the most influential parameter for PSD as compared with Af, As, and τf. For the CTD method, Af and As are seen to have less influence over the PSD compared to τf and τs when (Af τf/As τs)γ = 1 and τf is the most influential parameter for both reference pulses. Using both methods with either reference pulse applied, the scintillator having luminosity parameters such that is classified as having poor PSD. Excellent correlation is observed between the simulation and the experimental results with CsI:Tl, which is known for very good α/β(- γ) pulse shape discrimination. This study is useful for describing how the luminosity parameters affects PSD.