Residue, firearm

The concept of Neutron Activation Analysis (NAA) of barium and antimony present in primers as a means of firearm residue detection is now ten years old and it appears appropriate to point out the salient points of the development of the technique. 

The bivariate-log-normal analysis of data collected by Guinn and co-workers appears to be the only comprehensive statistical treatment of firearm residue detection by NAA (11). Suspects handswabs were interpreted in terms of accumulated firing test data and handblanks collected from individuals of different occupational backgrounds. A somewhat more empirical interpretation of the same data is also reported (12). Additional data from smaller scale collection of handblanks have been published recently (13,14). 

The final paper in this volume (Jones) is concerned with the application of a less familiar technique, photoluminescence, to a wide range of investigations, including sensitive firearm residue detection, the discrimination between different glass, polymer, and hair samples, and the identification of seminal stains. The promise here is of relatively inexpensive equipment with wide applicability in the criminalistics laboratory. 

J. S. Wallace, and R. H. Keeley, A Method for Preparing Firearms Residue Samples for Scanning Electron Microscopy, Scanning Electron Microscopy 2 (1979). 

At the start of 1978 the particle analysis method183 replaced the flameless atomic absorption bulk elemental method184 as the firearm residue detection method in the NIFSL. Since then the particle analysis method has been substantially improved by the use of a sample concentration/cleanup procedure,185 the addition of a backscattered electron detector, and the development of an automated residue detection system.186 187 Despite these improvements the technique remains costly and labor intensive. Certain aspects of the system required further work, in particular, the particle classification scheme discharge particles from mercury fulminate-primed ammunition and discharge particles from new primer types (Sintox). 

The detection and identification of the organic constituents in FDR has the potential to be used either as a screening technique or, much more likely, as a complementary technique to the particle analysis method. The particle analysis method has proved very satisfactory and has been well tried and tested in casework and court. The objective is to devise an efficient system for organic firearm residue detection that is entirely compatible with the particle analysis method. As a suspect may need to be examined for both firearm and explosive residue the method must also be compatible with organic explosive residue detection techniques. 

The ratio of indicative to unique particles is markedly different from that of firearm discharge. From firearm residue casework statistics, based on cases with at least one particle in the unique category, the ratio of indicative to unique particles is approximately 35 1. For starting pistol discharge residue particles the overall ratio is in the region of 1 10. 

In this part, the development of a clothing sampling method, common to both explosive and firearm residue is described. 

In the process of discharging a firearm, residue may or may not be deposited on the firer and when deposited the residue varies markedly in concentration. This occurs even with repeat firings under identical conditions where the only obvious variables are the date and time. 

Rowe WF (2000) Firearms residues. In Siegel JA (ed.) Encyclopedia of Forensic Sciences, vol. 2. San Diego Academic Press. 

Projectiles, cartridge cases, firearms residues in barrels of firearms and in gunshot entries Pb isotope ratios MC-ICP-MS [13]... 

Nondestructive NAA can thus be used for the detection and measurement of Ba, Sb (and also Cu) from residue samples collected from the floor surface after the single firing of a handgun. By constructing a unique distribution pattern of these residues, it is possible to establish the flight path of the bullet and the proximity of the gun with respect to the target. The development of this information, particularly in the absence of a firearm, a bullet or an eyewitness, can be of considerable value in criminal investigations... 

The NAA method for the determination of firearm discharge residue has been generally accepted, but applications have been limited to just a few laboratories. In the process of establishing NAA capability for the State of Illinois crime laboratories we re-examined the standard techniques (10). In the course of our work it became clear that post-irradiation is the cause of several constraints which have discouraged a more widespread use of NAA. The inherent time limitation due to the 87 min. half-life of 139Ba necessitates fast manipulations of radioactive solutions which in turn requires an experienced radiochemist. In addition to an ever present danger of overexposure and contamination, typically only a dozen samples can be irradiated per batch, which makes the method quite expensive. The developed statistical bivariate-normal analysis (11) is convenient for routine applications. With this in mind, a method was developed which a) eliminates post-irradiation radiochemistry and thus maximizes time for analysis b) accommodates over 130 samples per irradiation capsule (rabbit) c) does not require a collection of occupational handblanks and d) utilizes a simplified statistical concept based on natural antimony and barium levels on hands for the interpretation of data. The detailed procedure will be published elsewhere (15). 

Several techniques have been utilized for the detection of firearms discharge residue on the hands of an individual who has recently handled or discharged a weapon. Testing for the presence of nitrates proved unreliable and was discarded. Colorimetric tests for barium and antimony from primer composition were found to lack sufficient sensitivity for general application. 

Neutron activation analysis (NAA) with a rapid radiochemical separation has been the method generally used in recent years, but requires substantial investment, has high operating cost and limited availability. Modem flameless atomic absorption (AAS) instruments provide sensitivity approaching that of NAA and offer a viable alternative for the detection of firearms discharge residue. 

In 1959 Harrison and Gilroy (3) demonstrated the detectability of barium, antimony and lead in firearm discharge residue using a specific "spot" test for each element. Inadequate colorimetric sensitivity for barium and antimony (I4.) has severely restricted the use of the method as a field tool. 

The development of neutron activation analysis (NAA) as a sensitive and specific method of trace elemental analysis led to its application during the 1950 s for the detection of firearm discharge residue. Its ability to detect and identify very low concentrations of barium and antimony, elements associated with most primer compositions, was encouraging. 

A major problem confronting forensic laboratories interested in employing NAA is the scarcity of suitable reactor facilities. If firearms discharge residue analysis is to be widely employed, an alternate technique must be developed. Atomic absorption... 

Table III shows that two quite different analytical techniques, Flameless Atomic Absorption Spectroscopy and Neutron Activation Analysis, yield equivalent frequencies of detection of firearms discharge residue.

A "positive" firearms discharge residue result, as referred to here, is based upon occupational hand blank studies reported by several investigators (20,26,27,28). The 0.30 and 0.20 micrograin quantities for barium and antimony are conservative statistical estimates from average levels of these elements found in hand blank determinations. 

It should be further emphasized that the critical element in firearms discharge residue determination is Sb, because of its uncommon environmental occurrence. However, this common characteristic has led some investigators to consider using Sb alone for the determination of GSR (26). The two methods are in good agreement with regard to incidence of positives as indicated by Table III. 

Since both methods yield comparable results, which method should a laboratory use for firearms discharge residue detection Three factors must be kept in mind cost, turn-around-time and personnel requirements. 

In short, NAA is an excellent analytical tool, but for firearms discharge residue, FAAS is the more practical technique. 

Scott, H. D., Coleman, R. F. and Cripps, F. H. "Investigation of Firearm Discharge Residues" Atomic Weapons Research Establishment Report AWBE 0-5/66, England, (1968)... 

Numerous terrorist activities as well as many serious criminal offensives involve firearms. When a firearm is discharged, a variety of materials is emitted by the muzzle (accompanying the projectile), including primer and gunpowder (propellant) residues... 

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