Barack Obama has arrived in Europe for The Nuclear Security Summit at the Hague . An emergency G7 summit on the Ukraine crisis will be held on the sidelines of the nuclear summit . This was widely interpreted as a `` wake-up call '' about the possibility that a terrorist group could detonate a small nuclear weapon , or a radiological dispersal device ( a so-called `` dirty bomb '' ) . Comment: Obama sees enhancing global nuclear security as a key part of his legacy , Hammond says .
Barack Obama has arrived in Europe for The Nuclear Security Summit at the Hague . An emergency G7 summit on the Ukraine crisis will be held on the sidelines of the nuclear summit . Comment: Obama sees enhancing global nuclear security as a key part of his legacy , Hammond says .