Neutronic limits in various target mediums driven by a proton beam of 1 GeV energy

The concept of accelerator-driven system (ADSs) combines a particle accelerator with a subcritical core. The basic process in an AD is nuclear transmutation, and in general, an ADS consists of three parts: (1) accelerator, (2) spallation-neutron target (SNT) and (3) sub-critical core which surrounds the SNT. This study presents the neutronic characteristics of integral data in an infinite target medium driven by an isotropic point source of 1 GeV incident proton. Lead bismuth eutectic, mercury, tungsten, uranium, thorium, chromium, cupper and beryllium are considered as the target material because of their favorable spallation-neutron production characteristics. In order to be able to simulate the infinite target medium by eliminating the spatial dependence, a spherical target is considered, and its radius is increased gradually up to adequate radius ensuring the infinite target medium. In this way, the radius value ensuring the maximum neutron leakage out of the target would be determined. Numerical calculations were performed with the high-energy Monte Carlo code MCNPX in coupled neutron and proton mode using the LA150 library. The results bring out that a significant ratio (92-99%) of the leaking neutrons is below 20 MeV in the lead-bismuth eutectic, mercury, tungsten and uranium target materials. The maximum neutron leakage quantities for chromium, cupper and beryllium are an extremely low for a SNT