Hydrogen storage in metal hydrides has recently been studied as a possible way to store energy. One of the possible options is magnesium, which is abundant and cheap and it has a high hydrogen storage capacity. However, its ability to release the hydrogen fast is limited. To overcome this problem, alternative approaches have been developed including the use of nanostructures or thin film systems. Recently, the loading and unloading of Mg thin films have been studied with optical hydrogenography. Results were interpreted as a two-phase system (Mg / MgH2), where the kinetics are described by a nucleation and growth process. Studies of hydrogen loading of nano-sized Mg particles suggest more complicated kinetics. We propose to study this process in more detail by means of specular and off-specular neutron reflectometry.