Potential Applications of Instrumental Neutron Activation Analysis (INAA) to Forensic Investigations.

Instrumental Neutron Activation Analysis (INAA) is a non-destructive highly sensitive technique that can be used to determine the concentrations of approximately 40 elements at the ppm to ppb level. Samples are exposed to a thermal neutron flux and radioactive isotopes are produced. Samples are irradiated “as is”. No sample preparation is required other than ensuring that the sample will fit inside the irradiation vial. The artificially produced radioisotopes then decay via the emission of a beta particle and the accompanying emission of a set of characteristic gamma rays. A solid state detector is used to sense the emitted gamma rays. The gamma ray energies are used to identify the isotope and the intensities of the gamma rays are used to quantify the abundance of the isotope. After corrections for potential interferences, neutron dose, and decay, the elemental abundances are calculated by reference to single element standards. Virtually any solid material can be analyzed using this technique. Unlike solution based techniques, where complete dissolution is a concern, INAA returns the total elemental content of a sample.

Potential forensic applications include: (1) The identification of maple syrup and maple sugars. Different sources have different trace element characteristics. (2) Ceramics, which vary in trace element chemistry in response to both the materials used to make the ceramic and the glaze. (3) Source of grasses. Elemental characteristics vary, even for the same species of grass, as a function of the soils in which they grow. In principle it should be possible to geo-locate grass samples. (4) Because different substrates and catalysts are used in the production of nanomaterials it is possible to identify a specific source. This has proven to be very useful for carbon nanotubes, which are essentially insoluble, but can be easily characterize by INAA. (5) Differentiation between mineral, rock, and soil samples all of which may be similar at the macroscopic level but which are distinguishable on the basis of trace element differences.