Interception and Retention of Fallout by Desert Shrubs

Abstract

Abstract

Concentrations of 131I and 89Sr on plants contaminated by fallout from Project Sedan tended to decrease with increasing distance from ground zero and increasing time after the detonation. Microscopic and radiometric examinations of foliage indicated that most of the activity deposited on leaves was probably due to particles < 5 μ in diameter, and virtually none of it was due to particles >44 μ in diameter. A comparison between the theoretical and observed interrelations of gamma dose rates, 131I and 89Sr deposition rates, and 131I and 89Sr interception by desert shrubs indicated a deficiency of 131I relative to 89Sr in areas more than 40 miles from ground zero and an excess of both 131I and 89Sr relative to dose rates in areas about 100 miles from ground zero. The effective half lives of 131I and 89Sr on plants were shorter than their radioactive half lives, and a comparison of environmental half lives suggested that 131I may have been lost from plants by some process, such as vaporization, which had no effect on the retention of 89Sr. Statistical analyses indicated that the frequency distributions of variates representing maximum concentrations of 131I and 89Sr on plants, and in the tissues of rabbits collected at the same times and locations in the fallout field, were not normal but lognormal. Similar analyses indicated that the frequency distributions of effective half life estimates could be treated as either normal or lognormal.