Reparable and Irreparable Damage in Yeast Cells after Low LET-Irradiation
Diploid yeast cells in early Gl phase were irradiated with 60Co-γ-rays or 30 MeV electrons (mean LET, L̄ =0.2 keV/µm) and with x-rays (effective photon energy = 40 keV; L̄ = 3 keV/µm). The dose rates of the irradiation were so low (Ḋ = 27 rad/min) that maximum repair occurred during irradiation.
60Co-γ-rays produce no irreparable damage up to absorbed doses D of about 120 krads. X-rays on the other hand cause irreparable damage in the same dose range, yielding a survival fraction of 0.25 at D = 120 krads.
Comparing the cumulative fractional absorbed dose distributions in L100 for 60Co-γ-rays and for x-rays (Eeff = 40 keV), the irreparable damage due to x-irradiation cannot be caused by the high LET fraction of the absorbed dose (L ≥ 10 keV/µm). In fact, the x-ray-induced irreparable damage is caused by the fraction of the absorbed dose in the LET range from about 1 keV/µm to 10 keV/µm.
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- International Commission on Radiation Units and Measurements: Linear Energy Transfer, ICRU Report 16, p. 12, Washington, 1970Google Scholar