Calorimetric Analysis of the Effect of 60Co .GAMMA.-rays on the Growth of Saccharomyces cerevisiae.

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Using a heat conduction type multiplex calorimeter equipped with 24 calorimetric units the heat evolution from growing 60Co γ-irradiated Saccharomyces cerevisiae was detected in the form of growth thermograms. 60Co γ-irradiation affected the growth pattern in which a dose-dependent reduction of the growth rate constant was obsereved together with the retardation in growth, indicating an involvement of bactericidal and bacteriostatic effects. These effects were quantitatively analyzed in terms of the bactericidality as a function of dose intensity, which was defined in the previous paper.It was shown that the bactericidal effect of γ-ray irradiation was dominant within lower doses and decreased almost linearly with the increasing doses up to 3kGy. An equation to determine the number of survivors on the basis of the parameters calorimetrically determined was developed. The survival rate obtained by a proposed equation was in good agreement with that determined from the colony counting up to a dose range of 4kGy. However, a remarkable difference was found to exist between the two results obtained at doses higher than 4kGy. The discrepancy was discussed in terms of action mechanism of irradiation.
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