GEANT4 Simulation of the Gamma-Ray Total Absorption Facility

To fulfill the needs of neutron capture reaction cross-section measurement in the keV energy region in the field of nuclear astrophysics and advanced nuclear energy system development, the 4π BaF_2 Gamma-Ray Total Absorption Facility (GTAF) developed by the Key Laboratory of Nuclear Data of the China Institute of Atomic Energy (CIAE) was transplanted and installed at the Back-streaming White Neutron Source (Back-n) of the China Spallation Neutron Source (CSNS) in 2019. A series of results has been achieved and published based on the GTAF since then, and it has been identified that the need of reducing backgrounds is becoming increasingly urgent. In order to understand the origins of backgrounds and to optimize the facilities, a detailed simulation program using GEANT4 toolkits was established and is presented in this paper. The symmetry in the geometric arrangement of the 4π BaF2 detector array plays a critical role in ensuring uniform detection efficiency and accurate reconstruction of gamma-ray spectra, which is essential for neutron capture studies. To demonstrate the availability of the proven codes, several practical examples of assisting the process of experimental data and helping verify the optimization proposition are also shown in this paper.