In the real world, there are often many reasons _why_ this kind of analysis is used. As in the situations described here, it may be the only workable method. Sometimes there may be a choice of methods, but activation analysis is used because it has certain peculiar advantages or because it happens to be the most convenient. There are other times, however, when other analytical methods can and should be used. Such situations arise when the element sought is not easily activated, or when a satisfactory alternative method exists that is more economical or more convenient. The points to remember about the use of activation analysis are that: 1. In many cases, no elaborate sample preparation procedure is required. 2. For many elements, it is the most sensitive analytical technique known. The diversity of _applications_ in which activation analysis is used is enormous and will probably continue to be. The examples given here represent only a tiny fraction of circumstances in which the method has been used. Consider that it has been used successfully: 1. In the microscopic world of biology and medicine; 2. For meteorites arriving from the vast reaches of space; 3. In the production lines of consumer products; 4. For precious samples of moon rocks; 5. In the most “down-to-earth” business of hunting for new mineral sources; 6. For exploring the causes of Napoleon’s death nearly 150 years earlier (see photograph on next page). Today, there is virtually no field of science and technology that is untouched by this method. The illustrations of _procedures_ used in the situations described in this booklet are typical of some in use today. There are many other situations that require still other techniques. One of the most exciting, which will be used with increasing frequency in the future, involves the use of computers. It has been shown that data collected by high-resolution gamma-ray spectrometers can be “fed” directly to a computer. The computer can be programmed to identify unknown components and to determine the concentrations of elements of interest to the analyst. It is entirely possible to include corrections for radioactive decay, possible interferences from other elements present, and many other factors. It appears quite likely that the kinds of analyses described here (as well as others) may someday be accomplished automatically, with far smaller chances for error and probably more economically. [Illustration: Hair sample] Samples of Napoleon’s hair. Neutron activation analysis of these hairs revealed that he had been poisoned with arsenic. (He died, however, not from arsenic poisoning, but from acute mercury intoxication.)