Patent Number: 039327485
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to a method of determining the distance between an area under fire and the muzzle of the weapon by means of autoradiography of the irradiated firing residues on this area. Determining the distance between a fire arm and the point of impact is a very important problem in criminal investigation. In doubtful cases of suicide, justifiable self-defense, or even when determining whether a specific hole was caused by the impact of a bullet, the immediate environment of the point of impact is a very important source to be investigated. A large number of methods of identification of traces of shots are known; but, so far neither chemical analysis nor purely quantitative determination through neutron activation analysis (NAA) permit a satisfactory assessment of the distance to be made. Among other disadvantages, these methods do not operate in the non-destructive mode because the irradiated filters with the traces of shots had to be destroyed for measurement so that the spurious activity of the matrix was removed. Autoradiography has already been used to identify impacts of bullets as such by irradiating a piece of material fired at and afterwards contacting it with X-ray film. This film was then processed into prints or radiographs, respectively. However, this type of investigation of the hole made by a bullet does not allow any conclusions to be drawn as to the range from which a shot was fired. SUMMARY OF THE INVENTION The method according to the present invention in a general sense relates to the detection of the traces of antimony following the bullet and ejected by the weapon. These are always contained in the primer or in the bullet in addition to barium and lead. These particles accumulate on the material stopping a bullet as the bullet penetrates, and are retained and partly burned into this area. The characteristic distribution of such particles in the area around a bullet hole is unambiguous and cannot be placed there in any other way. As has been shown in qualitative analyses of the bullet, powder, primer and shell, the main source of the traces of antimony is the bullet, some of it stemming from the powder as well as the primer. Most probably a certain quantity is rubbed off the bullet as the bullet very rapidly passes the rifling on the inside of the barrel, follows the bullet as a powder or in molten form and is precipitated around the point of impact. As far as the analysis of traces at the point of impact is concerned, it is a particularly fortunate coincidence that the element antimony is very easy to ascertain after neutron activation. The present invention is concerned with a non-destructive and thus reproducible method which can be used to determine the distance between the point of impact of a bullet and a weapon. The structure of the background at which the bullet was fired should not be able to falsify the result, and the evaluation should be very simple and quick. In the present invention, this problem is solved in the method outlined above in that several carrier areas are fired at from various distances. The carrier areas afterwards are activated by neutron irradiation and then contacted with a film sensitive to nuclear radiation. The series of autoradiographs produced after development of the film are compared with the autoradiograph produced in the same way of the trace on the area under fire of the shot to be investigated and are used as a distance standard for that trace. In this method the carrier areas may be made out of the same material as the area under fire. For the case of a highly radioactive carrier area containing, for instance, antimony, it is suggested in accordance with the present invention that the residues of the shot after irradiation are transferred from the carrier areas and/or the area under fire onto a new carrier which is then used to produce the autoradiographs. In accordance with the present invention a very advantageous method of transfer is contacting the area containing the residues of the shot with an adhesive foil under pressure, afterwards separating the area and the foil from each other and covering the adhesive side of the foil with another foil. It is furthermore suggested in the present invention that the total density and the number of particles be measured either visually or by means of image analyzers in evaluating the autoradiographs as the distance standard.