Neutronic Calculations for the Shielding Design of the VESPA Instrument at the European Spallation Source

Abstract: The European Spallation Source is being built in Lund, Sweden and it’s planned to be the brightest pulsed spallation source for thermal and cold neutrons (<1 eV). Neutrons will be produced by a 2 GeV accelerated proton beam hitting a tungsten target wheel, then they are moderated by liquid hydrogen and water based moderator system and delivered to 42 beam-ports. Neutrons are transported via reflections to a set of instruments connected to the beam-ports through neutron guides. Undesired fast neutrons can cause a radiation safety issue, since they can find their way down the beam-lines and thus generate a large dose. A designed shielding structure is needed to minimize such effect during the beam at the target phase. We present the results of neutronic calculations to optimize the guide shielding for the VESPA instrument.