On the outside of the bomb there is a hard shell made of metal. Right underneath the shell there is a layer of explosives under the explosives there is a pusher under the pusher there is either Plutonium or Uranium 235. When the explosives explode they push the pusher that’s surrounding the metal you’re using into the metal making it much smaller than it was. The metal will shrink until there there is no space for it to get any smaller. The atoms inside the metal start to fire into each other causing fission. The atoms start to break apart into two when fission occurs. When an atom splits in half huge amounts of energy form. When an atom splits in half the two pieces fire into other atoms causing more atoms to split. This is called a chain reaction. All these atoms splitting let’s out tremendous amounts of energy. Finally the bomb shell cracks and the explosion occurs. This whole process takes approximately 0.0000000000018 seconds.
Radiation is formed because the smaller atoms that were part of the bigger atoms are unstable which means they let of radiation. There are three different types of radiation Alpha particles, Beta particles, and Gamma rays. The most dangerous type of radiation is called Gamma rays this type of radiation can enter your DNA and it can cause leukemia cancer and other types of cancer.
]A mushroom cloud is formed when all the heat released out of the bomb rises up which causes the stem part of the mushroom form and then the top part of the mushroom is formed when the heat of the bomb hits cooler air up in the atmosphere which causes it to flatten out.
If you would like to see an atomic bomb exploding click here.