Gamma radiation calculations and gamma blocker design for the high-energy beam transport region of the European Spallation Source

The purpose of this paper is to present the Monte-Carlo calculations performed to design a special element called gamma blocker (GB), necessary to stop the gamma radiation in the Accelerator-to-Target (A2T) section of European Spallation Source (ESS) linac. Very high levels of gamma radiation emitted backward from the activated target through the beam pipe could effectively block any human intervention close to the beam transport system. The residual dose rate in the linac tunnel was calculated without and with different GBs as a function of time. The final GB material and dimensions are proposed.