The nematode Caenorhabditis elegans is up to 39 times more sensitive to gamma radiation generated from 137Cs than from 60Co.

Survival after gamma irradiation (generated from either a 137Cs or 60Co source) was determined for two strains of the nematode Caenorhabditis elegans. Animals were between 1.3 and 39 times more sensitive to cesium than to cobalt. The magnitude of this differential sensitivity was dependent upon the strain, developmental stage and sex tested. Several control experiments eliminated trivial explanations for this difference. Since cobalt- and cesium-generated gamma particles have nearly identical energy depositions, the differential sensitivity likely reflects different mechanisms of processing the slightly different spectra of DNA damage induced by these two radiations. Sex-specific differences in radiation sensitivity were also noted and were likely due to the fact that males possess a single X chromosome rather than two, as do hermaphrodites.