Atomic Bomb

An Atomic Bomb is a Nuclear Weapon that creates an explosion through fission of a radioisotope at critical mass. The most common form uses a Radioactive element found in Seastone called Neptunium developed by Vegapunk using Ancient blueprints kept by the Sorcerers of Mahorela.

Mechanics
The most common form uses a radioactive element found in Seastone called Neptunium. According to Vegapunk the Neptunium found in Seastone is much easier to separate than those deposits found in other radioactive substances. Missiles equipped with warheads using this material are found on the Fallen Atlantis and the users of the Kaku Kaku no Mi can create these weapons at will. Explosives are employed as the implosion trigger that in turn press a tamper that causes a Critical Mass to undergo a Supercritical State and Explode in a Nuclear Inferno.

History of Usage
These weapons were used in the ancient war between the Great Kingdom and the Twenty Kingdoms. After which the weapons were quickly outlawed, that is until Vegapunk took up residence on Mahorela, where he rediscovered the secrets of Neptunium and began redeveloping nuclear weapons in secret for Mahorela in exchange for letting him study Sorcerer Culture. During the Mahorela Incident, the Sorcerers used these Atomic Weapons to destroy the Fleet of Marines wreaking havoc on their home. Any information remaining on these weapons are in the hands of the Archangel Pirates and the Revolutionary Army.

Trivia

 * Neptunium was chosen for this concept due to it's namesake and the fact it's never been used in Nuclear Weapons IRL due to it being difficult to separate from Uranium and Plutonium Deposits.