Simulations of Optical Photons for the EJ-309 Organic Liquid Scintillator

Liquid-organic scintillators play important role in many areas of research and field applications, including nuclear nonproliferation, reactor instrumentation, particle physics, material science, dosimetry, and astrophysics. The production of scintillation light as a result of particle interactions with the hydrogen and carbon nuclei is dependent upon the type and energy of the particle. The resulting recoil nuclei are charged particles which produce (typically) visible light in scintillators. Prompt and delayed scintillation light is emitted in transitions between singlet and triplet states of an organic molecule. The scintillation light is then collected by the photocathode through a coupler, converted into electrical signal, and amplified by a photomultiplier tube into a measurable voltage pulse. Studying the scintillation process of a detector through simulations is useful for gaining in-depth knowledge of the detector. Liquid scintillators are sensitive to both gamma rays and neutrons which require the knowledge of standard electromagnetic and hadronic physics processes. However, for detailed simulations, production of optical photons requires the implementation of additional processes such as scintillation, Cherenkov emission, bulk absorption, Rayleigh scattering, and boundary physics. This paper presents the scintillation response of EJ-309 liquid scintillator cells, simulated using the Geant4 Monte Carlo code. To the best knowledge of the authors, full optical-photon simulations have not been previously done for the EJ-309 liquid scintillator. This work will further enhance the Detection for Nuclear Nonproliferation Group’s simulation capabilities, which currently consist of the Monte Carlo code MCNPX-PoliMi with custom-made dataprocessing software.