Thoron radiation is a type of radiation with many uses.

It was used primarily as a method of interfering with sensors and transporter systems, (DS9: "Emissary", "The Way of the Warrior"; VOY: "Basics, Part II", "The Cloud") seen as a byproduct of alien appearances, (DS9: "If Wishes Were Horses"; VOY: "Sacred Ground") used for medical purposes, (VOY: "Basics, Part II", "Flashback") and used as a basis for weaponry (although it could result in instability in the weapon). (VOY: "Retrospect", "Warlord")

High levels of thoron radiation were found around the Nechisti shrine. (VOY: "Sacred Ground")

Antithorons can be generated on a large scale by Intrepid-class starships and have been used both to interfere with force fields and decontaminate planetary crusts prior to mining. (VOY: "Hunters", "Tattoo") Thoron radiation may also hinder transporter operations, presumably by interfering with sensor readings.

To 21st century science, thoron is a naturally-occurring radioactive isotope created by the decay of thorium. It is also known as radon-220, has a very short half-life of about one minute, exists as a gas at room temperature, and produces alpha radiation. It presents a radiation health hazard in nature much like radon, but is sometimes used in radiotherapy. To 24th century science, thoron radiation appears to be something wholly distinct from simple alpha radiation.
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