A nadion is an artificially-generated particle. Among other uses, phasers produce nadions when they are fired.
Nadion radiation would accelerate the development of Tuvan Syndrome. (DS9: "Inter Arma Enim Silent Leges")
During the Occupation of Bajor, Doctor Crell Moset exposed Tabor's grandfather to nadion radiation as part of his medical experiments. It took six days for Moset's victim to die. (VOY: "Nothing Human")
In 2367, a particle pulse gauged by Data and Geordi La Forge while verifying the origin of a Type-III phaser rifle, was later determined to be Romulan in origin. (TNG: "The Mind's Eye")
In an alternate timeline, in 2371, Captain Janeway closed a subspace fracture generated by the crew with her phaser, in order to avert a polaric ion explosion. On the other side, Lieutenant Torres registered a nadion particle resistance that was preventing them from opening the fracture. (VOY: "Time and Again")
In 2374, Tuvok tried to use nadion bursts to disperse the pool of Silver Blood that was threatening to sink USS Voyager. (VOY: "Demon")
In late 2375, Dr. Bashir suggested using nadion bursts to slow the progress of Odo's disease. (DS9: "Extreme Measures")
The Bussard collectors on an Intrepid-class starship do not produce nadion emissions. (VOY: "The Haunting of Deck Twelve")