Ultritium 283

From Memory Alpha, the free Star Trek reference.

Ultritium 283 is a form of ultritium, one of many explosive materials available to the crew of the USS Enterprise-D in 2367 when they were trapped in a Tyken's Rift.

According to the database, this material is an "industrial chemical explosive used in mining applications intended for precision-charge patterns using standard microwave pulse ignition devices." (TNG: "Night Terrors")

Atoms of this material appeared in an okudagram display of explosives listed in the Enterprise-D library computer.