Theory of RBE: Seventh triennial report, 1 January 1967 to 31 December 1987

This study investigates the probability of inactivation of the sensitive targets of a detector by gamma-rays as a function of dose can be mapped into the region surrounding the path of an energetic heavy ion through the ''local dose'' deposited by its delta rays. This system yields a detailed picture of the track of a single particle and a means of calculating the action cross-section. The action cross-section may be understood as the probability per unit path length of generating an observed end-point in a medium. We find the action cross-section for heavy ion interaction by radially integrating the probability. Our interpretation branches depending on whether the action cross-section is smaller or greater than its ''plateau value'', which is the case of cell killing or the induction of chromosome aberrations approaches the geometric cross-sectional area of the nucleus. We refer to the smaller cross-sections as in the track-width regime because of the characteristic appearance of these tracks, like an irregularly spaced string of beads or a hairy rope, respectively, where in nuclear emulsion one counts grains or measures the track width. Our ideas have resulted in a substantial clarification of radiation effects in a variety of detectors, including biological cells. For 1-hit detectors we can predict the high LET response from their response to gamma rays, and conversely we can predict the response to gamma rays if we know the high LET response over an adequate range of bombardments. Biological cells have a more complex structure. We cannot predict their detailed high LET response from their response to gamma rays