Thermionic radiation is a form of energetic radiation.

The atmospheres of Y-class planets emit discharges of thermionic radiation, that can pose a threat to starships in orbit. (VOY: "Demon")

Thermionic radiation is harmful to lifeforms, but dissipates relatively quickly. In 2376, Captain Rudolph Ransom claimed that the USS Equinox's research lab was inaccessible due to thermionic radiation. Seven of Nine later discovered that the radiation was being deliberately maintained by three EPS conduits, to keep the USS Voyager crew from discovering their exploitation of nucleogenic lifeforms. (VOY: "Equinox")