Lateral distribution of the 10B isotope within a boron carbide film of 550 nm maximum thickness deposited on silicon wafer using pulsed laser deposition technique has been determined taking advantage of the high cross section for (n,α) reaction and nuclear tracks detectors (NTD - LR-115 Kodak Pathé). A radioisotope neutron source (252Cf, 20 μg) and a 60 × 60 × 80 cm3 graphite cube as moderator produce a relatively uniform thermal neutron field. Details of the passive detector etching process and data processing are included. The track density reveals the boron density spatial distribution. A 3D picture is produced to visualize the boron-10 spatial distribution. The result suggests that a gradient in the boron distribution exists to almost a factor of three. The advantages of the technique are discussed. © 2009 Elsevier Ltd.