A new hybrid gadolinium nanoparticles-loaded polymeric material for neutron detection in rare event searches

Experiments aimed at direct searches for WIMP dark matter require highlyeffective reduction of backgrounds and control of any residual radioactivecontamination. In particular, neutrons interacting with atomic nuclei representan important class of backgrounds due to the expected similarity of aWIMP-nucleon interaction, so that such experiments often feature a dedicatedneutron detector surrounding the active target volume. In the context of thedevelopment of DarkSide-20k detector at INFN Gran Sasso National Laboratory(LNGS), several R&D projects were conceived and developed for the creation of anew hybrid material rich in both hydrogen and gadolinium nuclei to be employedas an essential element of the neutron detector. Thanks to its very highcross-section for neutron capture, gadolinium is one of the most widely usedelements in neutron detectors, while the hydrogen-rich material is instrumentalin efficiently moderating the neutrons. In this paper results from one of theR&Ds are presented. In this effort the new hybrid material was obtained as apoly(methyl methacrylate) (PMMA) matrix, loaded with gadolinium oxide in theform of nanoparticles. We describe its realization, including all phases ofdesign, purification, construction, characterization, and determination ofmechanical properties of the new material.