This study presents the neutronic behavior of integral data in an infinite target medium driven by an isotropic point source of 1000 MeV incident proton. Lead-bismuth cutectic, mercury, tungsten, uranium, thorium, chromium, copper and beryllium are considered as the target material because of their favorable spallation-neutron production characteristics. Furthermore, the calculations are performed for also dual mixture of some of them. 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 mixing of the LBE with a solid target material (such as W, U and Th) lowers significantly the target radius ensuring the maximum neutron leakage. (c) 2007 Elsevier Ltd. All rights reserved.