. Elementary biophysics: selected topics . 10 20 30 X-ray dose (kr) 40 Fig. 54. Bacterial survival after various x-ray doses. The age of the culture in hours is listed with the survival curve for bacteria of that age. (From Stapleton, J. Bacteriology, 20, 357, 1955; courtesy the author and Williams and Wilkins Co., Baltimore, Md.) we obtain a multitarget curve as a result of an experiment, we simply draw a line of the same slope so as to pass through the 100% survival point, and we can then calculate the value of n. In addition, from the mononucleate survival curve, we can find the 37% surviva
. Elementary biophysics: selected topics . 10 20 30 X-ray dose (kr) 40 Fig. 54. Bacterial survival after various x-ray doses. The age of the culture in hours is listed with the survival curve for bacteria of that age. (From Stapleton, J. Bacteriology, 20, 357, 1955; courtesy the author and Williams and Wilkins Co., Baltimore, Md.) we obtain a multitarget curve as a result of an experiment, we simply draw a line of the same slope so as to pass through the 100% survival point, and we can then calculate the value of n. In addition, from the mononucleate survival curve, we can find the 37% survival dose, and then obtain the radiosensitive volume as before. The value of n can also be found by extrapolating the straight-line portion of the survival curve back to the zero dose line; the intercept is the nuclear number itself. That this is true can be seen from the last equation: log (N/N0) = log n — D. If we set D equal to zero, we obtain log (N/N0) = log n. This way of finding n is illustrated in Fig. 53 by extrapolating the n = 2 and n = 10 curves back to the zero dose line. The student should be warned that there are serious possible com- plications which can arise in a radiobiological experiment. For example, there are cases of irradiation of polyploid yeasts in which the target
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