The decrease in radionuclide concentration from a contaminated pasture, and the effect of rainfall on the removal of this deposited activity were determined on 3 experimental plots (220 m2), which were prepared by transplanting the upper 10 in. of a Wisconsin-type soil profile plus a 2 in, sod layer. In the spring of 1966, 10 niCi each of R5Sr and 134C:s was deposited over 140 m2 of this area with a controlled spraying mechanism. Portions of the grass were protectd from precipitation by automatically closing covers. The height of the grass in discrete plots was 2 in. or 6 in. Replicate samples from the protected plots were clipped at intervals of 1-8 days, while the exposed sections were sampled after each of the 20 rains during the 75-day expcriment.The disappearance curves, from a statistical analysis of the activity per dry weight, showed two effective half-times. For the protected areas, the first component was approximately ten days for *%r and fifteen days for 134Cs. The second component for both tracers ranged from 25 to more than 50 days. Samples from the exposed areas were generally lower in activity after each rain. The first half-time component for s5Sr and lsaCs averaged 3 -4 days, respectively, whereas the second component for the exposed area ranged from approximately 25 to more than 50 days.
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