Cell inactivation studies on yeast cells under euoxic and hypoxic condition using electron beam from microtron accelerator

In the case of sparsely ionizing radiation such as electron, the dose rate and the pattern of energy deposition of the radiation are the important physical factors which can affect the amount of damage in living cells. In the present study, the differences in the cell survival efficiency and dose rate effect in diploid yeast strains Saccharomyces cerevisiae X2180 and Saccharomyces cerevisiae D7 under euoxic and hypoxic condition have been quantified. Irradiation was carried out using 8 MeV pulsed electron beam from Microtron accelerator. The dose per pulse and pulse width of the beam used was 0.6 Gy and 2.3 μs, respectively, which correspond to an instantaneous dose rate of 2.6 × 10⁵ Gy s⁻¹. For survival studies doses were delivered at a rate of 50 pulses per second (an average dose rate of 1,800 Gy s⁻¹). Fricke and alanine dosimeters were used to measure the dose delivered to the sample. A significant difference in the dose response has been observed under euoxic and hypoxic condition. Dose rate effect has been studied by changing the pulse repetition rate of the Microtron and the dose rate used was from 180 to 1800 Gy min⁻¹. A significant dose rate effect was observed under euoxic condition for Saccharomyces cerevisiae X2180 but the same was absent under hypoxic condition. The dose rate effect was absent for Saccharomyces cerevisiae D7 under both irradiation condition. The survival curves are found to be sigmoidal in shape under both condition but with a wider shoulder under hypoxic condition. The D₀ value and the Oxygen Enhancement Ratio (OER) at that point have been derived.