Development of a Single Target Pattern

Expanding target patterns in the Belousov-Zhabotinsky reaction were first discovered by Zaikin and Zhabotinsky (1970). In their experiment, they used a spontaneously oscillating thin layer of solution which was contained in a Petri dish of diameter 100 mm. The reagent contained bromate, bromomalonic acid and ferroin. With this prescription, one may observe periodic alternation of oxidized and reduced forms of the catalyst through a dramatic color change of the solution between red (reduced state) and blue (oxidized state). Some features of the pattern observed by them and by later experimenters are the following .  

1) Blue waves are sent out periodically from an isolated point (called a pacemaker), and they propagate outward in the form of concentric rings or a target pattern. 

2) Some such target patterns may coexist in the same medium. The frequencies at which the waves are emanated, which we call the pacemaker frequencies, differ from pacemaker to pacemaker, but they are definitely higher than the frequency of the uniform oscillation. 

3) The propagation velocity of the waves is approximately the same for all target patterns which coexist. These waves can be blocked by impermeable barriers, implying that they represent trigger waves. 

4) The waves annihilate each other on head-on collisions. Consequently, a pair of colliding circular waves forms an angular structure in the wave front. 

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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... 

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