The oxygen effect has been studied in Escherichia coli B/r irradiated with high-intensity pulsed electrons as a function of oxygen concentration. The dose to the cells was delivered in single pulses of time duration 30 nanoseconds. As was observed previously at low oxygen concentrations, survival measured under pulsed conditions for higher concentrations is greatly different from that obtained under relatively low-dose-rate conditions. Typically, the survival curve for cells which are pulse-irradiated follows the oxygenated response to a point dependent on concentration before breaking away to parallel the slope of the survival curve measured under conditions of pure nitrogen. A plot of the "break-point dose" versus oxygen concentration appears linear. The data can be interpreted as further support for a hypothesis based on oxygen depletion within the cell by the first part of the electron pulse previously proposed for Serratia marcescens pulse-irradiated at low oxygen concentrations. The data can also provide a basis for the direct measurement of oxygen diffusion time in cells.

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