Today the most reliable method for detecting gunshot residue is through the combined use of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In recent years, this same methodology is beginning to find use in detecting and characterizing pyrotechnic reaction residue particles (PRRP) whether produced by explosion or burning. This is accomplished by collecting particulate samples from a surface in the immediate area of the pyrotechnic reaction. Suspect PRRP are identified by their morphology (typically 1 to 20 micron spheroidal particles) using a SEM and then analyzed for the elements they contain using X-ray EDS. This can help to identify the general type of pyrotechnic composition involved. Further, more extensive laboratory comparisons can be made using various known pyrotechnic formulations.
In planning and interpreting airborne gamma‐ray surveys, an important consideration is the relative contribution of surface areas of a homogeneous radioactive source to the detected radiation. Numerical calculations have shown that along a flight line the width of the strip that produces a fixed percentage of the detected radiation is significantly less than the diameter of the circle contributing the same percentage of the radiation detected by a stationary gamma‐ray detector. Experimental angular sensitivity measurements of typical sodium‐iodide detectors were incorporated into the calculations and showed that the results were not strongly dependent on the detector configuration. The results are shown to have applications in estimating the count rate from small sources and in the design of an optimum ground survey grid for test strips selected for the calibration of airborne gamma‐ray spectrometers.
Several electrooptic digital light deflection techniques have been proposed. The maximum number of resolvable deflection positions for all methods is determined, essentially, by economic reasons, the tolerable amount of background light, and aberrations. In this paper, three different types of deflection methods (split angle, total internal reflection, Wollaston prism) are described. Design, construction details, and performance of three deflector models are reported. Combined deflection systems use the advantageous properties of each of these methods to economically obtain the maximum number of resolvable deflection positions. A suggested combination to achieve 1024x1024 positions arranged in a two-dimensional field would consist of one total internal reflection stage, seven stages of split angles, and two stages of Wollaston prisms for each dimension.
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