The approximation in the formulation for survival S = exp - (αD+βD2)

Attention is given to the nature and limitations of the approximation of this survival formula to the model based on the assumption that a break in the DNA double helix is the primary lethal lesion. Poisson statistics have been used to predict the chance of survival. It is concluded that the formula is valid for the purposes of interpretation either at very low dose or for very high values of m (the number of site-pairs corresponding to lesions), but not at high doses and with small values of m. (UK)