Radioactivity Processes - Smoke Alarms & Nuclear Fission

• The Alpha particles ionise the molecules of the air forming ions & electrons which are attracted to a pair of charged plates.
• When the ions & electrons hit the plates they provide a small amount of electricity.
• This current stays constant & is monitored by the smoke alarm
• When smoke enters the smoke detector, the smoke particles near to the radioactive source absorb many of the alpha particles before they can ionise the air between the charged plates decreases & so the current which is passed also decreases.
• The smoke detector notices the decreases in current & sets off the alarm

Nuclear Fission is used to release energy form large unstable atoms by splitting them into smaller atoms.

• Usually, the nucleus has to absorb a neutron before it will split.
• When the atom splits it forms two new lighter elements that are roughly the same size.
• Two or three neutrons are also released when an atom splits. 
• If any of these neutrons are moving slow enough to be absorbed by another nucleus, they can cause a chain reaction.
• The energy not transferred to the nuclei is given out /carried away as gamma rays

• The amount of fission in a nuclear reactor is controlled by changing how quickly the chain reaction can occur.
• This is done using control rods, which are lowered are lowered and raised inside a nuclear reactor to absorb neutrons, slow down the chain reaction and control the amount of energy released
• Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion - this is how nuclear weapons works