Biomedical subjects

Robert D Koons

Publications and source records attributed to Robert D Koons.

4 recordsLinked to original sources

PubMed2005

Forensic significance of bullet lead compositions.

The concentrations of seven elements in projectile lead specimens received as evidence were used to assess the frequency of the occurrence of two unrelated samples having indistinguishable compositions. A set of data from 1837 samples was selected for this study from a sampling of 23,054 lead bullets and shot pellets received as evidence in the FBI Laboratory over the period 1989 through 2002. The method used for selection of samples from case submissions ensured that no two samples of the same general type from the same case were included and that no bias was introduced concerning representation of manufacturers or production sources. A total of 1,686,366 pairwise lead sample comparisons were made using the concentrations of the elements Sb, Cu, As, Ag, Bi, Sn, and Cd using a match criterion of two times the sum of the standard deviations of the paired samples. Of the 1837 samples, 1397 samples, or 76%, are distinguishable from every other sample in this study. The total number of indistinguishable sample pairs is 674, for a frequency of 1 out of every 2502 comparisons. The frequency of occurrence of matching samples decreases as the number of measured elements is increased and as the precision of the measurements improves. For bullets in which all seven elements were determined, the match frequency is 1 in 7284. Compositional comparison of bullet lead provides a reliable, highly significant point of evidentiary comparison of potential sources of crime-related bullets.

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PubMed2005

Development and evaluation of a standard method for the quantitative determination of elements in float glass samples by LA-ICP-MS.

Forensic analysis of glass samples was performed in different laboratories within the NITE-CRIME (Natural Isotopes and Trace Elements in Criminalistics and Environmental Forensics) European Network, using a variety of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) systems. The main objective of the interlaboratory tests was to cross-validate the different combinations of laser ablation systems with different ICP-MS instruments. A first study using widely available samples, such as the NIST SRM 610 and NIST SRM 612 reference glasses, led to deviations in the determined concentrations for trace elements amongst the laboratories up to 60%. Extensive discussion among the laboratories and the production of new glass reference standards (FGS 1 and FGS 2) established an improved analytical protocol, which was tested on a well-characterized float glass sample (FG 10-1 from the BKA Wiesbaden collection). Subsequently, interlaboratory tests produced improved results for nearly all elements with a deviation of < 10%, demonstrating that LA-ICP-MS can deliver absolute quantitative measurements on major, minor and trace elements in float glass samples for forensic and other purposes.

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PubMed2002

Interpretation of glass composition measurements: the effects of match criteria on discrimination capability.

The concentrations of ten elements in 209 unrelated glass specimens received as evidence were used to assess the frequencies of errors of false association (Type II errors) using several comparison criteria at specified significance levels (Type I errors). Pairwise comparisons of the samples using either the equal-variance t-test or Welch's modification (unequal variances) result in a small number of errors of false association, even when adjusting the significance level (Bonferroni correction) for multivariate comparisons. At the 95% confidence level (overall Type I error of 0.05, or individual element comparison error of 0.005), only two Type II errors are made in 21736 comparisons (0.009%) when using the equal-variance t-test for comparison of sample means. In this study, the range overlap test using three replicate measurements per specimen results in no errors of false association. Most specimen pairs in this data set are readily discriminated either by differences in the concentrations of several elements or by an extremely large difference in the concentrations of one or more element.

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PubMed2002

Compositional variation in bullet lead manufacture.

The concentrations of antimony, copper, tin, arsenic, silver, bismuth, and cadmium in lead alloys produced by two smelters and one ammunition manufacturer were determined using inductively coupled plasma-atomic emission spectrometry. These element concentrations were used to measure the variations in composition of lead products that result from various processes involved in the manufacture of lead projectiles. In general, when a pot containing molten lead is used to cast a number of objects, these objects are similar, although not necessarily analytically indistinguishable in their elemental compositions. In each subsequent step in the processing of lead at the smelter and at the ammunition manufacturer, the size of an individual homogeneous melt of lead decreases as more distinct compositions are formed as a result of remelting and mixing of sources, including lead scrap. The ammunition manufacturer in this study produced at least 10 compositionally distinguishable groups of bullet wire in a 19.7-h period. The largest group could potentially be used to produce a maximum of 1.3 million compositionally indistinguishable 40 grain bullets.

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