In a recent publication (1), Nelson develops a modified description of the dose–response relationships for the yields of free radicals trapped in irradiated solids. He notes that the shape of the curves obtained when plotting such relationships has mostly been well described by the (1— exp) form originally found by Rotblat and Simmons (2), but he points out that deviations from this form occur at very high doses. The purpose of my communication is to offer alternative thoughts on the reasons for these deviations.

During the course of their original investigations, Rotblat and Simmons were possibly the first to observe that, at doses above about 50 Mrad (5 × 105 Gy), the ESR spectrum obtained from irradiated glycine decreased significantly in amplitude. These observations were noted briefly in ref. (2) and described in detail in a second...

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