Cobalt bomb
From Memory Alpha, the free Star Trek reference
A Cobalt bomb was a type of nuclear weapon that had less than 1/10,000th of the destructive yield of an ounce of antimatter.
In 2268, Ensign Garrovick compared the explosive forces of the two weapons to Captain James T. Kirk. (TOS: "Obsession")
An ounce of antimatter corresponds to an explosion of 1.22 megatons. This indicates 23rd century cobalt bombs had yields of less than 122 tons of TNT.
