Activation calculations for the target of a spallation ultra-cold neutron source at PSI

A spallation ultra-cold neutron source--UCN source--is scheduled to start operation at PSI in 2006 using up to 2 mA 590 MeV protons from the ring cyclotron. It will be operated in a pulsed mode with an average current of 20 microA. For safe maintenance, during operation as well as handling, transport and storage of the UCN target assembly after its lifespan, detailed knowledge about the activation induced by the impinging protons and secondary radiation fields is required. The Monte Carlo transport code MCNPX was coupled with the European Activation System--EASY--to calculate the residual nuclide production in the UCN target assembly. The nuclide inventory is finally used to design the shielded exchange flask that is needed to safely remove and transport the UCN target assembly after its lifespan to a hotcell for dismantling.