A hybrid Exponential-Gaussian approach for pulse shape modeling in liquid scintillators

We present a bi-Exponential-Gaussian Hybrid (EGH-2) model to quantitatively characterize scintillation pulse shapes generated by neutrons and γ-rays in the BC501A organic liquid scintillator detector. Pulses were recorded digitally from a mixed radiation field produced by an Am-Be source across eight different Light Output (LO) windows spanning 150 keVee to 4 MeVee, at a sampling rate of 2.5 GSa/s and 12-bit ADC resolution. High-confidence neutron and γ-ray pulses were identified in each LO window using the Discrete Wavelet Transform Method (DWTM) and the Charge Comparison Method (CCM). The resulting pulse shapes are found to exhibit asymmetric Gaussian profiles with well-defined rise times and slow decay components, which are effectively captured by the EGH-2 model. The model demonstrates high fidelity in replicating both the fast rise and prolonged decay characteristics of neutron and γ-ray pulses across the full energy range. For each LO window, the central values and spread of all the fitting parameters are presented for both particle types, enabling their potential use in reconstructing the simulated pulse shapes within the required LO window. The proposed EGH-2 model provides a reliable and physically meaningful approach to model pulse shapes in organic scintillators.