NORTH DAKOTA
| Bismarck | 46D 46M North / 100D 45M West |
| Fargo | 46D 54M North / 96D 46M West |
| Williston | 48D 11M North / 103D 38M West |
SOUTH DAKOTA
| Aberdeen | 45D 27M North / 98D 26M West |
| Huron | 44D 23M North / 98D 13M West |
| Rapid City | 44D 03M North / 104D 04M West |
| Sioux Falls | 43D 34M North / 96D 44M West |
TEXAS
| Austin | 30D 18M North / 97D 42M West |
| Corpus Christi | 27D 46M North / 97D 30M West |
| Houston | 29D 58M North / 95D 21M West |
| San Antonio | 29D 32M North / 98D 28M West |
WASHINGTON, D.C.
| Dulles Airport | 38D 57M North / 77D 27M West |
| National Airport | 38D 51M North / 77D 02M West |
WYOMING
| Casper | 42D 55M North / 106D 28M West |
| Cheyenne | 41D 09M North / 104D 49M West |
| Lander | 42D 49M North / 108D 44M West |
| Sheridan | 44D 46M North / 106D 58M West |
Radioactive fallout is created by thermonuclear weapons as a result of residual radiation, that is, radiation that occurs or is induced in particulate matter approximately one minute after detonation. In thermonuclear weapons especially, large numbers of high-energy neutrons are produced, which interact with elements in the air and on the ground; these elements then become radioactive and in turn emit beta and gamma radiation.
Fallout may be considered of two kinds: early and delayed. Early fallout occurs within 24 hours and is the most severe. Fallout of this type produces contamination and presents a biologic hazard. Delayed fallout produces very fine particles of radiated material that are spread in the atmosphere. The hazard with delayed fallout is long term, especially because of elements with very long half-lives, such as cesium 137 and strontium 90.
Airbursts are more likely to produce delayed fallout because of the height of detonation. Surface bursts, conversely, produce fallout that is more localized but more intense.
Radioactive particles generally vary in size from 1 micron to several millimeters. The larger particles tend to fall within 24 hours and are the most radioactive. Between 50 and 70 percent of total radioactivity is produced as early fallout.
Weapons can be made to produce larger amounts of radioactive elements, hence the term “dirty weapons.”
