Initial radioactive contamination fallout

The following steps give an indicative estimate of the dose from the fallout of an explosion  

This method does not take into account the shielding effect of the ground roughness, nor the dimensions of the initial radioactive cloud. These effects, given the largely indicative character of these estimates, are to be considered as secondary. 

Rain or snow are much more important than these effects on the distribution of the contamination by causing a washout of the radioactive cloud and a patchy distribution of the unit dose. 

---

Half-lives span a very wide range (Table 17.5). Consider strontium-90, for which the half-life is 28 a. This nuclide is present in nuclear fallout, the fine dust that settles from clouds of airborne particles after the explosion of a nuclear bomb, and may also be present in the accidental release of radioactive materials into the air. Because it is chemically very similar to calcium, strontium may accompany that element through the environment and become incorporated into bones once there, it continues to emit radiation for many years. About 10 half-lives (for strontium-90, 280 a) must pass before the activity of a sample has fallen to 1/1000 of its initial value. Iodine-131, which was released in the accidental fire at the Chernobyl nuclear power plant, has a half-life of only 8.05 d, but it accumulates in the thyroid gland. Several cases of thyroid cancer have been linked to iodine-131 exposure from the accident. Plutonium-239 has a half-life of 24 ka (24000 years). Consequently, very long term storage facilities are required for plutonium waste, and land contaminated with plutonium cannot be inhabited again for thousands of years without expensive remediation efforts. 

Epidemiological studies of populations in the FSU exposed to fallout from the 1986 nuclear reactor explosion at Chernobyl and releases from the Chelyabinsk-65 complex demonstrate the health effects associated with exposure to radioactive iodine, strontium, and caesium. A study of 2.81 X 10" individuals exposed along the Techa River, downstream from Chelyabinsk-65, revealed that a statistically significant increase in leukemia mortality arose between 5 yr and 20 yr after the initial exposure (37 observed deaths versus 14-23 expected deaths see Cochran et al. (1993) and cited references and comments). There has been a significant increase of thyroid cancers among children in the areas contaminated by fallout from the Chernobyl explosion (Harley, 2001 UNSCEAR, 2000). The initial external exposures from Chernobyl were due to and short-lived isotopes. Subsequently, external exposures to Cs and nd internal... 

---