Astatine

Astatine is a radioactive element.

A planet in the Orellius system colonized in 2360 by the SS Santa Maria's colonists had several deposits of astatine. The colonists believed the astatine was the source of the duonetic field that prevented their technology from working. In 2370, Miles O'Brien discovered the astatine was not the source, as in actuality it was a device of Alixus' design. 

In 2381, the Starfleet Corps of Engineers team on the USS Musgrave used astatine to no success in an attempt to destroy the farantine deposits on Maxia Zeta IV.