Antimatter radiation

From Memory Alpha, the free Star Trek reference.

Antimatter radiation is a type of radiation emitted by antimatter. Exposure to the radiation can cause severe illness and even death. In high enough doses, it can disintegrate organic tissue.

In 2374, Dejaren claimed to B'Elanna Torres that the lower deck of his ship was flooded with lethal antimatter radiation. However, this was a lie to prevent her from discovering the bodies of the murdered crew. (VOY: "Revulsion")

In 2377, the USS Voyager discovered that the Earth probe known as Friendship 1 had inadvertently led to an antimatter disaster on a planet in the Delta Quadrant. The atmosphere had been heavily contaminated with antimatter radiation, devastating the population. Voyager eventually cleared the radiation by triggering an isolytic reaction with its photon torpedoes. (VOY: "Friendship One")

Theta radiation is likely a related form of radiation.

Although it was never specifically referenced on-screen, the type of radiation to which Spock was exposed in Star Trek II: The Wrath of Khan when he was attempting to fix the warp drive of the USS Enterprise may have been antimatter radiation. Then again, warp cores are also known to emit theta radiation and neutron radiation.