Fallout 137Cs: Direct aerial transfer as an important source of foliar deposition

Abstract

Listen

Translate article

A 4 acre stand of alfalfa was systematically sampled and analyzed for 137Cs during the 1965 growing season. In addition, the deposition of fallout 137Cs in rainfall and surface air concentrations were measured. A small section of the field was covered to exclude fallout deposition by rainfall. The 137Cs in alfalfa in the open field increased during rainless periods, while during the rainy periods the alfalfa levels often decreased. While the levels in the open field were higher than under the shelter, the differences were not great enough to indicate that deposition from rainfall was a primary factor in the contamination of alfalfa in the normal environment. Overall deposition velocities for transfer of surface air 137Cs to vegetation were calculated by neglecting the possibility of contamination for rain, but considering the exponential decay-rate of deposited 137Cs. Overall deposition velocities were calculated for transfer of surface air 137Cs to vegetation without regard for deposition from rain in the open field and compared with the deposition velocities calculated for the covered alfalfa. For a first cutting of alfalfa, which grew from late May through July, the deposition velocities were 920 and 690 m/day, for unsheltered and sheltered alfalfa, respectively. The equivalent deposition velocities for a second harvest were 260 and 310 m/day for unsheltered and sheltered alfalfa.