Comment, the Evidentiary Uses of Neutron Activation Analysis
Dennis S. Karjala
Arizona State University College of Law
California Law Review, Vol. 59, p. 997, 1971
Neutron activation analysis (NAA) is a method of detecting with great sensitivity the presence and concentrations of most chemical elements in materials, without, in most cases, destroying the sample analyzed. It permits identification and measurement of concentrations of elements which are present in only minute or trace quantities, such as specks of paint, which because of their size are not susceptible to other techniques. Also, under appropriate circumstances, NAA can identify both large and small pieces of material by accurately analyzing their trace element concentrations. Such identifications rely on the fact that, although concentrations of the major constituents of similar specimens such as two pieces of glass may be nearly the same, impurity trace elements sometimes show a wide variation from one source to another because manufacturers make no effort to control the quantities of these elements in their products. Besides its high sensitivity, NAA's potential for nondestructive measurement provides the further advantage that the samples which are measured can be preserved for production in court or for further tests.
NAA, properly applied, can be a valuable forensic tool. However, the interpretation of the analysis presents difficult legal problems that depend almost entirely on the circumstances of the individual case. The analytical chemist is qualified to present the results of the analysis, but his subjective interpretation, as a chemist, is worthless; an expert in statistics is required to present a legal interpretation of the analysis. The expert must have a solid, objective basis for any statement beyond the composition of the measured samples, and the burden of laying an objective foundation for the testimony should rest on the party seeking to introduce the results of the tests. The expert must use well-defined terms which fit the legal issue presented by the facts of the case, and must present his testimony in such a way that the trier of fact clearly understands the limitations of the analysis.
Number of Pages in PDF File: 84
Keywords: Neutron Activation Analysis, Forensics, Evidence
Date posted: July 23, 2009
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