Thermal neutrons are captured by several elements which emit charged particles as reaction products. These particles leave etchable damage tracks in detector materials placed against a sample, creating a map of the distribution and concentration of the target element. The most common applications are for trace U using fission fragment tracks and B using alpha tracks. Li, N and possibly S and O can also be determined. We have applied the technique to B in metals and coatings, Li in Al, N in glass and U in O-ring seals. Dectection limits are better than 10−11g/g for U, 10−9g/g for B, 10−6 g/g for Li and 0.1 wt % for N. Spatial resolution for mapping is about 25 μm.