Samples which have been irradiated in a thermal neutron flux are first allowed to decay for an appropriate period. The distribution of isotopes which decay by beta emission is then detected using a specific nuclear track emulsion. Data are presented to show the relative sensitivities of all elements which emit beta particles after thermal neutron capture and to demonstrate their relative rates of decay. The technique may be used most sensitively to locate minerals containing high concentrations of Sc, Co, Y, Sb, Cs, rare earth elements, Ta, Re, Ir, Au, Th, and U. Potential applications in the systematic search for rare earth element-bearing minerals in granitic rocks and platinum-group element minerals in chromitites.--Modified journal abstract.