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Recent analyses of track structure show that the parameters describing a radiation field are not separable from those describing a detecting system; that is, it is impossible to write an expression describing the effect of irradiation as a product of 2 factors, one of which contains only parameters describing the detecting system, while the other contains parameters describing only the radiation field. From this perspective it is difficult to understand the use of a “quality factor,” applicable to all biological substances and given as a function of the “effective LET,” for the conversion of rads to rems. One cannot define, nor can a single instrument measure, a universal “radiation quality.”
Nevertheless, it is possible to generate a useful, simplified description of the interaction of a radiation field with a particular detector in a particular ambient environment, by specifying the “equivalent track-segment bombardment.” For cells, this is the bombardment yielding equal survival for equal dose, under the specified conditions.