The areas in which plutonium contamination would be significant enough to require evacuation and subsequent decontamination are roughly estimated to be about 100 times the areas subjected to a lethal dose. About a dozen grams of plutonium dispersed throughout the largest enclosed building in the world might make the entire building unusable for the many weeks that would be required to complete costly decontamination operations.

The dispersal in large open areas of plutonium with lethal concentrations of radioactivity is likely to be much more difficult to carry out effectively than dispersal indoors. The height of the affected zone would be difficult to hold down to a few feet. Even a very gentle, two-mile-per-hour breeze would disperse the suspended material several kilometers downwind in an hour. This would make it extremely difficult to use less than about one kilogram of plutonium to produce severe radiation hazards. With a few dozens of grams of plutonium, however, it would be relatively easy to contaminate several square kilometers sufficiently to require the evacuation of people in the area and necessitate a very difficult and expensive decontamination operation.

After the plutonium-bearing particles settled in an area, they would remain a potential hazard until they were leached below the surface of the ground or were carried off by wind or surface water drainage. As long as the particles remained on the surface, something might happen to draw them back into the air. Contamination levels of about a microgram of plutonium per square meter would be likely to be deemed unacceptable for public health. Thus, in an urban area with little rainfall, a few grams of plutonium optimally dispersed out of doors might seriously contaminate a few square kilometers, but only over a very much smaller area would it pose a lethal threat.

So far in our discussion, we have considered only plutonium–239, the isotope of plutonium that is produced in the largest quantities in nuclear reactors. Plutonium–238, which is also made in significant quantities in some reactors, is considerably more toxic than plutonium–239. Its half-life for emitting alpha particles is only about eighty-seven years, instead of about 25,000 years; one gram of plutonium–238 therefore emits alpha particles at approximately 300 times the rate that plutonium–239 does. As a result, the lethal dose of plutonium–238 is about 1/300 of what it is for plutonium–239. We mention this because plutonium–238 has been used in radioisotope-powered nuclear "batteries," and is being seriously considered for use in power supplies for heart pumps in people suffering from certain types of heart disorders. As much as sixty grams of plutonium–238, the equivalent in toxicity of almost twenty kilograms of plutonium–239, may be in each such heart-pump battery. This is enough material to produce serious contamination of hundreds of square miles, if dispersed in the form of small particles.

A variety of ways to disperse plutonium with timed devices are conceivable. These would allow the threatener to leave the area before the material is dispersed. Any plutonium contained inside such a device would not be a hazard until it was released.