Abstract
Accurate reconstruction of neutron spectra is essential for fissile material identification and nuclear safeguard applications. However, most existing studies only reconstructed neutron spectrum above 1-2 MeV, leaving the detector response in low energy region poorly constrained. This study introduces a unified experimental-simulation framework for high-fidelity spectrum unfolding in EJ-301 liquid scintillators. Detailed Geant4 Monte Carlo simulations were performed to model energy deposition and light-output processes for both gamma rays and neutrons, generating ideal response functions. To reproduce real detector behavior, energy-resolution parameters were experimentally calibrated using Compton-edge measurements from (137)Cs and (22)Na sources for 1-inch and 2-inch detectors. Validated by accurate reconstruction of (22)Na gamma spectra, the calibrated response matrices were then applied in iterative unfolding algorithms(GRAVEL and MLEM) to reconstruct the neutron spectrum of a (252)Cf source. The proposed approach achieves a lower energy threshold of 0.35 MeV and maintains an average deviation below 4.28%, with the best agreement of 1.42% from ISO 8529-1 reference data. The 2-inch detector demonstrated higher efficiency and resolution. This experimentally validated framework bridges the gap between ideal simulations and practical detector performance, providing a robust pathway for precise neutron spectroscopy and quantitative nuclear safeguards verification.