Detection of Gunshot Residue on the Hands by Neutron Activation and Atomic Absorption Analysis

Neutron activation analysis (NAA) for antimony and barium has been described as the most effective technique for the detection of gunshot residues on the hands of a suspect [1,2]. The method, however, is not used routinely for a number of reasons. Among the reasons are the complex nature of the statistical treatment of the data and the difficulty experienced by individual laboratories of collecting the voluminous background data required for these calculations. One of the important aspects of the technique is that the sample has to be collected with extreme care so that the contamination is minimal. Because the amounts of the elements analyzed are at microgram levels, specially designed procedures and training are required to be able to collect the samples without contamination. The existing techniques, such as paraffin lift and cotton swabbing, are found to be unsatisfactory in this respect. By taking repeated samples from hands by these procedures, it was found that three or four collections are required for complete removal of the trace elements. Thus, a single collection by these methods is not quantitative, and therefore, any subsequent calculation would be in error.