A Liquid Scintillation Detector for Radioassay of Gadolinium-Loaded Liquid Scintillator for the LZ Outer Detector

Understand

We report on the design and performance of the LUX-ZEPLIN (LZ) "Screener", a small liquid scintillator detector consisting of $\approx 23$ kg of LAB-based gadolinium-loaded liquid scintillator (GdLS) to be used in the LZ Outer Detector.

• The Outer Detector will be filled with 17.3 tonnes of GdLS and will surround the central liquid xenon time projection chamber of LZ.
• Its primary function will be to veto neutron single-scatter events in the liquid xenon which could mimic a WIMP dark matter signal.
• To meet the requirements for the Outer Detector, the radioimpurity levels in the GdLS must be kept below $\lesssim0.07$ mBq/kg.