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

TL;DR

This paper investigates the fundamental mechanisms of scintillation and quenching in liquid scintillators, emphasizing molecular and dielectric properties that influence efficiency and discussing specific loading schemes like TeBD.

Contribution

It provides a detailed analysis of excitation, ionization, and recombination processes, and links molecular polar groups and dielectric constants to scintillation efficiency and quenching.

Findings

Polar groups and high dielectric constant can cause quenching.

The dielectric constant of TeBD is measured as 16±1.

Hydroxyl groups contribute to quenching in TeBD.

Abstract

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 discussed, highlighting the processes of excitation, ionization, and anion-cation recombination. 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 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 for the first time, the relative dielectric constant of TeBD is measured to be $16\pm1$. These discussions explain part of the quenching of the TeBD liquid scintillator.