Development of a target imaging system for the European Spallation Source

At the European Spallation Source (ESS) neutrons will be produced by a proton beam impinging on a rotating target wheel. The technology of the target wheel, which comprises a large number of closely spaced tungsten bricks and is cooled by helium, is largely untested. The durability of the target wheel and hence the overall ESS neutronic performance depend on the integrity of the tungsten bricks. In order to monitor whether the target geometry is preserved over the expected 5 year lifetime of the target wheel, we propose a Target Imaging System (TIS). The TIS consists of a scintillator array detecting the collimated single photon emission (decay gammas) from the activated tungsten bricks. Preliminary Monte Carlo simulations support the feasibility of this imaging system. As a proof-of-principle, an experimental test-rig is being constructed allowing to test the main aspects of the imaging system under conditions relevant to ESS.