Peripheral blood analysis of numbers, n, of eLTRC surviving irradiation plotted as a function of dose. Seventy-day n, □; and 130-day n, ▪. Because of the break in the curve below 4.0 Gy, the regression line was fitted by least-squares method to data points from 4.5 Gy to 6.5 Gy for the 130-day samples. Negative inverse of the slope or D₀ was calculated to be 0.82 Gy ± 0.27 Gy (mean ± SE). The y-intercept or total number, N, of eLTRC per mouse was calculated to be 8,709, +32,299, −6,859 cells (mean ± SE). The 7.0-Gy data points were corrected for survival as described in text. Dotted lines define n = 1.36 for the observed LD_50/30 of 7.15 Gy.