Particle distributions, entering the vacuum tube, from an 80 x 80 x 60 cm3 lead target.

The neutron Time of Flight (n_TOF) facility at CERN is a source of neutrons produced by spallation of 20 GeV/c protons onto a solid lead target. The outstanding characteristics of this facility (very high intensity, 200m flight path, wide spectral function) make it an extremely useful tool that provides the necessary data for the design and understanding of Accelerator Driven Systems. Simulating geometries like the n_TOF tunnel, with a long flight path, and with the imposed background conditions, is a very difficult and time consuming task. To accomplish it, several software packages have been assembled using specially written interfaces. This report, describes the simulations performed, for the collection of data of the particles entering the neutron tube, necessary for the subsequent parametrization of their distributions.