Molecular structure, electric property, and scintillation and quenching of liquid scintillators

Liquid scintillators are widely used in particle and nuclear physics. Understanding the scintillation and quenching mechanisms is a fundamental issue in designing a high-light-yield liquid scintillator. In this work, the basic scintillation process for two-component liquid scintillators is reviewed, highlighting the processes of excitation, ionization, anion-cation recombination, and electric dipole-dipole energy transfer. A molecule's polar group, polarization characteristics, and the corresponding material's dielectric constant are found to be correlated with a liquid scintillator's scintillation efficiency. Polar groups and high relative dielectric constant (permittivity) can cause severe quenching and should be avoided. The tellurium loading scheme in the liquid scintillator of the SNO+ experiment, TeBD, is discussed. The hydroxyl groups introduce polar structures in the TeBD, and the relative dielectric constant of our reproduced sample is measured to be $17\pm2$. These discussions explain part of the quenching of the TeBD liquid scintillator.