A field study was carried out in which a beta-emitting fallout simulant was applied to a 35-day-old pea crop. Upon deposition of the simulant, almost all of the material came to rest on the soil surface and not on the plant. A dosimetry system was developed for measurement of the beta dose received by the plants. The fallout simulant consisted of yttrium-90 fused on very fine sand. An application of <tex-math>$55\ {\rm mCi}/{\rm m}^{2}$</tex-math> resulted in a surface dose of 1,690 rads to plant tissue in the region of the shoot meristems. This level of radiation reduced yield of peas to 39% of the control. Higher radiation levels reduced pea yield to zero, but 38,500 rads were required to materially reduce vegetative growth. Thus it was observed that reproductive tissue was much more sensitive to beta-radiation damage than was vegetative tissue. On the basis of theoretical calculations, it is suggested that the beta-radiation component in fallout may be more significant than the gamma component in adversely affecting the yield of a pea crop under the condition of this experiment.

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