The main purpose of the experiment proposed here is to study the effects of thermalisation on Artificial Spin-Ice (ASI) systems formed by nanomagnets with sub-100 nm lateral dimensions, by means of Polarized Neutron Reflectivity (PNR) analysis on different Bragg peaks. With this experiment we will be able to prove the existence of ground-state ordering in sub-100 nm ASI systems, as well as to quantitatively determine the disorder (deviation from ground-state) for any magnetization configuration present in the ASI pattern. These measurements will be the first-ever proof of the existence of ground-state ordering in sub-100 nm ASI systems, as current imaging techniques used so far to image ASI systems are beyond the resolution limit for such small nanomangets.