A radiolytic isotope, also referred to as neutronic radiation, was a particle which was toxic and deadly within three minutes to Humans, Vulcans, and Denobulans, among other species. Takrets were known to be immune to it.

In 2152, Enterprise NX-01 encountered a massive neutronic storm which was saturated with radiolytic isotopes, forcing the crew to take refuge in the catwalk, a maintenance shaft running the length of one of the warp nacelles. (ENT: "The Catwalk")