Critical values of linear energy transfer, dose rates and doses for radiation hormesis

Estimates are given of the critical values of linear energy transfer (LET), dose rate and dose, below which radiation hormesis is likely to occur but above which it is unlikely to occur. The critical value of LET is estimated to be 15 congruent to 20 keV/micron, and hence radiation hormesis may occur with beta, gamma or x rays, but is unlikely to occur with alpha radiation. The critical value of dose rate is estimated to be 1 congruent to 10 mGy d-1 for the lifetime exposure, but could be higher than this value for the short period exposure. These estimates are consistent with experimental data. The critical value of dose is also estimated, but cannot be compared with experiment because of lack of data. Brief comparison of plants with animals is made, and it is suggested that the value of the critical dose rate for plants in dry conditions, such as seeds or bulbs, could be higher than the above estimate by about a factor 1000. Some sociological considerations are also given.