A liquid scintillator for a neutrino Detector working at -50 degree

TL;DR

This paper reports the development of a liquid scintillator capable of operating at -50°C for a neutrino detector, ensuring transparency and performance with SiPMs by addressing water content and solubility issues.

Contribution

The study introduces a low-temperature liquid scintillator formulation with enhanced transparency and stability suitable for neutrino detection at cryogenic temperatures.

Findings

Water removal improves transparency at low temperature

Ethanol addition maintains fluor solubility at -50°C

Gd-doped LS shows good transparency and light yield

Abstract

A liquid scintillator (LS) is developed for the Taishan Antineutrino Observatory (TAO), a ton-level neutrino detector to measure the reactor antineutrino spectrum with sub-percent energy resolution by adopting Silicon Photomultipliers (SiPMs) as photosensor. To reduce the dark noise of SiPMs to an acceptable level, the LS has to work at -50 degree or lower. A customized apparatus based on a charge-coupled device (CCD) is developed to study the transparency of the liquid samples in a cryostat. We find that the water content in LS results in transparency degradation at low temperature, which can be cured by bubbling dry nitrogen to remove water. Adding 0.05% ethanol as co-solvent cures the solubility decrease problem of the fluors PPO and bis-MSB at low temperature. Finally, a Gadoliniumdoped liquid scintillator (GdLS), with 0.1% Gd by weight, 2 g/L PPO, 1 mg/L bis-MSB, and 0.05% ethanol by weight in the solvent LAB, shows good transparency at -50 degree and also good light yield.