Fluorescent nuclear track detector (FNTD). (a) Two FNTDs (8 × 4 × 0.5 mm3). Courtesy of M.S. Akselrod, Landauer Crystal Growth Division. (b) Fluorescent image of the 270.55 MeV u −1 carbon-ion tracks propagating perpendicular to the FNTD crystal surface. The brightest spots (physical energy deposition events) are attributed to carbon ions with a full width half maximum (FWHM) of approximately 500 nm . The smaller, less intense spots to less densely ionizing particles like protons. The small structures around the carbon ion tracks arise from secondary electrons (sec e-) . Insert: magnification of a single track spot. The track core is encoded by dark red. Scale bar, 5 μ m. (c) FNTD image after carbon irradiation (initial 270.5 MeV u −1) parallel to the polished crystal surface. Secondary electron structures (small trajectories branching from the ion track) are visible. Instead of homogeneous energy deposition discrete blobs (bright spots) occur along the particle tracks. This is an illustration of stochastic nature of energy deposition along the heavy charged particle track. Courtesy of F. Lauer. Scale bar, 5 μ m.