Gadolinium-Based Hybrid Ultra-Low-Background Material for Protecting the Darkside20k Dark Matter Detector from Background Neutrons

A laboratory technique was developed for obtaining an ultra-low-background hybrid material based on organic glass — polymethyl methacrylate (PMMA). 157Gd nuclei are used as an efficient absorber of thermal neutrons in the hybrid material. A uniform distribution of gadolinium in the PMMAmatrix is achieved by introducing the gadolinium in the form of a coordination compound — gadolinium acetylacetonate — into the hybrid material. A uniform gadolinium distribution was achieved in a 5 cm thick matrix of hybrid material with gadolinium mass content from 1.0 to 1.5%. It is shown that at 298 K the mechanical characteristics of the hybrid material samples coincide with nominally pure PMMA, but at 77 K the hybrid material is inferior to pure PMMA within admissible requirements.