Detection efficiency of the ESS target imaging system: Monte Carlo simulations

A Target Imaging System (TIS) is proposed for the European Spallation Source (ESS) aiming at detecting damaged areas of the spallation wheel, e.g. due to erosion or cracking of the spallation tungsten bricks. The TIS is a collimator imaging camera consisting of an array of scintillators individually coupled to an image-intensified sCMOS camera; the TIS records the 1D radial distribution of decay gammas from the activated target material while 2D image reconstruction is achieved through rotation of the target wheel. To investigate the efficiency of the TIS in detecting errors in the tungsten brick geometry, numerical simulations of the gamma fluxes are performed using MCNPX and CINDER90 software packages and image reconstruction algorithms are described that will allow detection of anomalies, e.g. in the form of brick fragments trapped in the cooling channels between the tungsten bricks. Preliminary results indicate that the TIS will be capable of detecting such anomalies in the target wheel.