Ponente
Descripción
DarkSide-20k is a direct dark matter search experiment, that looks for Weakly Interacting Massive Particle (WIMP) events. The detector is based on an ultrapure liquid Argon double-phase Time Projection Chamber, which will be located at Laboratori Nazionali del Gran Sasso. In rare event search experiments (like the DarkSide case), it is crucial to keep under control any background sources. In particular, one of the most dangerous background sources are neutrons, which could induce nuclear recoils, producing a signal indistinguishable from that of the WIMPs. The strategy adopted in the DarkSide-20k experiment is to build a neutron veto detector, made of a thick plastic layer containing gadolinium, which has a high neutron capture cross section. The construction of 17 cm thick plates made of polymethylmethacrylate (PMMA) doped with a compound containing gadolinium was therefore adopted. The choice of PMMA is due to the high hydrogen content of this polymer, to moderate the neutrons. Then thermal neutrons will be captured on the gadolinium nuclei and will be revealed, exploiting the subsequent emission of an easily-detectable high energy γ ray cascade in the surrounding liquid Argon. All the components of the composite material must be screened to identify any traces of elements (such as uranium, thorium and potassium) whose descendant radioactive isotopes could affect the performance of the experiment. The DarkSide collaboration has developed two strategies for the realisation of gadolinium doped PMMA sheets, using two gadolinium-containing compounds: Gadolinium methacrylate and gadolinium oxide in the form of nanograins and the first strategy has been chosen for the construction of DS-20k detector. The contribution reviews the innovative working principle of the DarkSide-20k veto and the development of these innovative materials focusing especially on the gadolinium oxide strategy.
