A Changed Dose-response in Saccharomyces at Dose-rates above 10⁷ Rad Per Sec

Summary

The dose-response of a haploid wild-type Saccharomyces and its mutants r^s₁ and r^s₂ to ionizing radiation of a dose-rate of 1·2 × 10⁷ rads/sec and 1 pulse per second was compared with that of dose-rates of 1·6–9·8 × 10⁹ rads/sec and varying pulse frequencies in hypoxic conditions.

Lower dose-rate exposures produced exponential, higher dose-rate exposures concave survival curves. Budding cells did not influence the shape of the survival curves.

At the 10 per cent survival level, all cells are 30 per cent less sensitive at the lower than at the higher dose-rates. At lower survival levels the situation reverses. The change in sensitivity may be due to a fast healing process at the lower dose-rates and radical–radical interactions at higher dose-rates.