We ask for 4 days beam time on GEM to study the dehydrogenation and subsequent rehydrogenation of Mg(11BD4)2. Mg(BH4)2 is currently one of the most promising lightweight hydrogen storage materials. We have shown that dehydriding begins to occur at 500K releasing 14.4 wt% and that ~6.1wt% can be reversibly stored subsequently. We believe that MgB12H12 is a likely intermediate and are asking for beam time on GEM to study the initial dehydrogenation and subsequent rehydrogenation using the IGAn. This experiment will allow us to measure the mass loss and gain in these processes while studying the detailed crystallography of the various phases produced during the experiment. There are amorphous components and we will perform a full PDF analysis of these phases. A detailed structural understanding of the 6.1wt% reversibility will help give us important insights into borohydride systems.