Use of photoluminescence to investigate apparent suicides by firearms.

A photoluminescence technique, which detects lead and antimony in gunshot residue, was evaluated for use in investigations of apparent gunshot suicides. The study was conducted in conjunction with forensic science laboratories in five U.S. cities. Samples were collected by the adhesive lift method from the backs of the hands of 67 gunshot suicide victims, 41 subjects who died of other causes, and 31 live subjects with high occupational exposure to lead and antimony. Tentative simultaneous threshold levels of 0.85 microgram for lead and 0.01 microgram for antimony were selected as criteria for presuming the presence of gunshot residue on samples from the hands of these suicide victims. Although blood decreases the detectability of lead and antimony in the samples, 48% of the suicide cases involving handguns other than .22 revolvers exceeded the threshold levels for both lead and antimony. Methods are suggested for eliminating the effects of blood, which should significantly increase the success rate for cases involving these guns. A much lower success rate was obtained for cases involving .22 revolvers and long guns, as expected from the sparse amounts of residue found in previous test firings of these guns.

Evaluation of a photoluminescence technique for the detection of gunshot residue.

More than 170 gunshot residue samples were analyzed by the inorganic luminescence technique to assess various factors affecting the utility of this and similar methods of elemental gunshot residue detection. Indoor firings consistently produced more residue in samples than did outdoor firings. Experiments were conducted to determine the effects of activity after firing on the ability to subsequently detect residue in samples. It was shown that residue can be transferred from hand to hand and can be detected in pockets under suitable conditions. Antimony, when present in the ammunition, was found to be the most useful indicator for the presence of residue, in that nearly all firings resulted in more Sb than was found in any of 45 handblank analyses obtained in these studies. Data obtained with a .32 pistol suggest that Sb normally exceeds environmental levels when residue is collected from the hand following delays up to several hours after firing. However, it will rarely exceed the currently used threshold levels of 0.1 to 0.2 microgram. Therefore, elemental analysis is best suited to screening applications for which threshold levels can be greatly reduced.

Carbon: a suggested new hexagonal crystal form.

Evidence for a new polymorphic form of carbon, similar to but distinct from chaoite, has been discovered. It is trigonal, with a(0) = 5.33 angstroms and c(0) = 12.24 angstroms. It is produced along with chaoite on the surfaces of graphitic carbons under free-vaporization conditions at low pressures, with temperatures above approximately 2550 degrees K.