The imaging semiconductor pixel detector Timepix allows measurement of charge collected in each of its 256x256 pixels (55 um pitch). This feature makes it suitable for applications where energy and position of incoming radiation needs to be measured. We are developing a novel fast neutron spectroscopy and radiography technique based on tracking of protons recoiled by fast neutrons. The proposed setup consists of a polyethylene (PE) bead placed above the Timepix detector surface and irradiated by fast neutrons. Protons recoiled by neutrons from the PE bead hit the detector and generate a track. Analysis of the track gives energy, position and direction of flight of the proton. This information is used to reconstruct energy of the incoming neutron. The neutron source position can be calculated as well. If both the source position and spectrum are known, the PE bead can be replaced by an unknown hydrogen rich sample and 3D tomographic reconstruction of the sample can be done. A Monte-Carlo simulation of the fast neutron detection process was prepared. The code was based on combination of ROOT and SRIM/TRIM packages. The proton recoil and transport through the geometry was simulated. Energy deposited in the detector for each event was calculated. The code contains also a model for charge sharing between pixels to correctly simulate the detected proton tracks. Results of simulations compared with experiment and details of the neutron source spectrum/position and object 3D reconstruction is presented.