Abstract
An apparatus designed to simulate the decay of radioactive fallout from nuclear detonations is briefly described and data are reported from experiments undertaken to determine the relative effectiveness of similar total exposures of 137Cs gamma radiation given at uniform exposure rates vs. simulated fallout decay. Seedlings of pea, maize, cabbage and radish were given three different treatments (16-hr and 36-hr uniform dose-rate exposures, and a 36-hr simulated fallout decay exposure with changing dose rates). Seedlings were exposed to 137Cs γ-radiation and transplanted to the field (maize and cabbage) or moved to a greenhouse for observation (radish and pea). Data on plant survival, gross vegetative growth, crop yield and pollen abortion are reported from scorings made weekly for up to about three months. Comparisons were made among the three radiation treatments for the survival end points (LD 10, LD 60, LD 90 and LD 100) and the 50 per cent reduction in fresh weight and crop yield. In all experiments the simulated fallout decay gamma exposure produced more deleterious effects than an equivalent total exposure delivered at uniform rates. (The 16-hr exposure produced more severe effects than similar exposures delivered in 36 hr.) When the results of 36-hr uniform exposures were compared to those from the 36-hr simulated fallout decay, the average increase in effectiveness varied from a factor of 1·79 to a factor of 2·04, with the average for all end points being 1·93 (almost a factor of 2 greater). Exposures which gave reductions of 50 per cent in fresh weight and crop yield for the same two radiation treatments varied by a factor of 1·59 to a factor of 2·11 with an average increase in effectiveness for all end points of 1·80 for the simulated fallout exposures. Predicted ld 50 s for 16-hr uniform and 36-hr FDS exposures based on measured interphase chromosome volumes are given for 49 varieties of economic plants.
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