Thorium
Thorium is a metallic element, number 90 on the periodic table, and a member of the actinide series. It is slightly radioactive.

During the Bajoran political coup d'état of 2370, a group of Starfleet officers led by Dr. Julian Bashir captured a five-man unit of Militia members loyal to the Alliance for Global Unity in Deep Space 9's Cargo bay 6. The doctor warned the Bajoran soldiers that their health would eventually be compromised by prolonged radiation exposure from a container of thorium isotope stored among the cargo bay's inventory. ()

When Benjamin Sisko asked Miles O'Brien to give his son some engineering experience, but not make it too easy, O'Brien replied that he would have Jake "up to his elbows in thorium grease." ()

In 2370, the Maquis Sakonna asked Quark to obtain for her some cobalt-thorium devices, among other weapons. ()

On the mirror universe  in 2370, the mirror  told  that the station's thorium containment cells needed to be upgraded. The Kira Nerys and Julian Bashir from the prime universe later used a thorium leak as cover from their escape. ()

The technology of the Caatati is dependent on thorium isotopes. When the Borg assimilated their homeworld, they lost the knowledge to synthesize thorium. In 2374, Seven of Nine provided the surviving Caatati with an energy matrix to synthesize thorium, allowing them to become self-sufficient again. ()

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Elements