An exploratory study of a tellurium-loaded liquid scintillator based on water and p-dioxane

TL;DR

The paper investigates a surfactant-free, water-containing approach to loading tellurium into a liquid scintillator based on p-dioxane, naphthalene, and PPO, aiming to enable high Te loadings for neutrinoless double-beta decay searches. By constructing a TeA–water–p-dioxane phase diagram and evaluating fluorescence, absorption, and relative light yield against a LAB–PPO reference, the study reveals a fundamental trade-off: increasing tellurium loading or water content enhances Te incorporation but quenches scintillation light, while incorporating naphthalene helps mitigate quenching up to practical solubility limits. TeA itself reduces light yield, likely by disrupting energy-transfer processes, even though TeA absorbs little in the PMT window. The results provide practical benchmarks for designing high-loading, surfactant-free, water-containing scintillators and guide future investigations into the mechanisms by which inorganic dopants affect scintillation efficiency.

Abstract

Tellurium-loaded liquid scintillators are critical for neutrinoless double-beta decay experiments. However, conventional organic scintillators are constrained by the limited solubility of organic tellurium compounds compared with that of inorganic ones in water, whereas water-based scintillators are likely constrained by the destabilization of surfactants caused by inorganic tellurium compounds. In this work, a surfactant-free water-containing route is explored, in which an aqueous telluric acid solution is introduced into a water-miscible organic scintillator comprising p-dioxane, naphthalene, and PPO. The phase behavior of this system is mapped to delineate homogeneous-mixture domains and to estimate practical upper bounds on tellurium loading. Optical properties are characterized by UV-visible absorption spectroscopy and fluorescence spectroscopy. The scintillation light yield is obtained with a relative method that compares to a reference LAB-PPO scintillator. The measurements demonstrate scintillation quenching induced by water and by tellurium acid. These results provide benchmarks for water-containing and surfactant-free formulations and support the development of high-loading liquid scintillators for future detector design.

Figures (11)

• Figure 1: Ternary solubility phase diagram for the TeA--water--p-dioxane system, showing the boundary between soluble and insoluble regions.
• Figure 2: Maximum naphthalene solubility as a function of water content in p-dioxane solutions. The dashed line serves as a visual guide.
• Figure 3: Fluorescence emission spectrum of p-dioxane excited at 185nm with a low-pressure mercury lamp.
• Figure 4: Fluorescence emission and absorption spectra of (a) 10mg/L naphthalene in ethanol, excited at 283nm, and (b) 10mg/L PPO in ethanol, excited at 330nm.
• Figure 5: Fluorescence emission spectra of p-dioxane alone and in mixtures with naphthalene and/or PPO, compared with the quantum efficiency of bialkali PMTs (plotted in red).