Biophysical studies with spatially correlated ions

An analysis is given of previously reported results of experiments in which cells have been irradiated with pairs of ions of variable mean separation.These studies were motivated by the theory of dual radiation action and specifically by the postulate that the lesions responsible for cell impairment by ionizing radiation are formed by the combination of pairs of sublesions that are molecular alterations produced by individual energy transfers in the cell nucleus.It is concluded that the observations are consistent with dual radiation action, and the most striking finding is that there appears to be a bimodal distribution of interaction distances with maxima at less than 0.1 and more than 1 /xm.Single tracks cause primarily the lesions produced in short-range interactions but they also contribute, at least in late S phase, a relatively small proportion of the long-range interactions which are principally due to a twotrack mechanism.The experiments suggest that the radiation-sensitive components of the cell are arranged in a highly nonuniform pattern which may take the form of floccules having diameters of less than 100 nm.