Dry Artemia eggs were used to determine the biological effectiveness of a 29-MeV electron beam at depths of 2.3 cm (2× 108 rads/second), 11.3 cm (1× 108 rads/second), and 13.0 cm (5× 107 rads/second) in a water phantom. It appears that a significant difference in effectiveness exists at these three depths as measured by the hatchability and hatching delay of the eggs. The effect at the 11.3- and 13-cm depths is 1.16 and 1.32 times greater than at the 2.3-cm depth. Experiments to determine the effect of dose rates ranging from 1× 107 to 2× 108 rads/second at the same depth demonstrated an apparent lower effectiveness of radiation exposure when delivered at extremely high dose rates. From the results of these experiments, we conclude that the difference in biological effectiveness of 29-MeV electrons at various depths is the result of a dose-rate effect.

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