Material assay campaign of the DarkSide-20k experiment.

The DarkSide-20k experiment will search for dark matter in the form of WIMPs and has the potential to set the best limits for the spin-independent interaction of heavy WIMPs with nucleons (90% CL for σSI=10−48 cm at WIMP mass Mχ = 100 GeV/c2). The requirement for backgrounds of radiogenic origin is fewer than 0.1 events in 10 years of exposure. Such a stringent goal has not been achieved to date and imposes the establishment of rigorous requirements in terms of radiopurity of the detector materials. A thorough assay campaign has been running for five years to assess the radiopurity of candidate components, paying particular attention to the uranium and thorium decay chains. Different assay techniques are exploited: ICP-MS is sensitive to the chain precursors (232Th and 238U); HPGe to the gamma emitters through the chain; Po radiochemical separation to the often-ignored 210Po content in the bulk of the materials. In such a way, it is possible to have accurate estimates of the background accounting for the breaking of the secular equilibrium of the uranium decay chain in all the materials. Beyond its common application, mass spectrometry is used for assessing the overall chemical composition of critical items, focusing on the quantification of elements with high (α,n) cross section, hence minimizing the uncertainty in the neutron yield. In this work, the organization of the assay campaign and its results to date are presented. [ABSTRACT FROM AUTHOR]