Nuclear Fission and Fusion

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Nuclear Fission

• Nucleus of an atom is bombarded with neutrons to split the heavier nucleus into smaller and lighter nuclei
• This makes the nucleus so unstable that it splits into 2
• A lot of energy is released
• Occur artificially
• Little energy is required to split an atom
• Atomic bomb is based on concept of nuclear fission
• Often involves releases of gamma rays and free neutrons ${}_0^{1}n{+}_{92}^{235}U-{>}_{56}^{141}Ba{+}_{36}^{92}Kr+3_0^{1}n$

Nuclear Fusion

• 2 or more lighter nuclei combine to form a heavier nucleus
• An enormous amount of energy is released, much larger than nuclear fission
• Occurs in stars and the sun
• Huge amount of energy is required to bring 2 atoms together
• Therefore, happens in very, very hot conditions
• Cold fusion is a concept that entails nuclear fusion happening at room temperature
• Hydrogen bomb is based on concept of nuclear fusion
• Usually releases neutrons or protons as well as new nucleus
• Strong magnetic field is required for magnetic confinement
• Ensures plasma doesn’t escape
• Confinement ensures that fusion occurs, and makes it safe

Mass defect

• The total mass of a stable nucleus is always less than the combined masses of the nucleons
• Mass defect: difference between total mass of the individual nucleons, and the mass of the nucleus as a whole 
• The difference in mass is considered to be the binding energy of the nucleus
• We can calculate the energy through $e=m{c}^2$
• e = energy in J
• m = mass in kg
• c = speed of light, or 300 000 000 m/s

Binding Energy

• The difference in mass (mass defect) is considered to be binding energy
• If the mass of 4He was equal to the mass of 2 protons + 2 neutrons, the nucleus would fall apart without any input of energy
• To be stable, its mass must be less than that of its constituents combined 
• The nuclear binding energy represents the amount of energy that must be put into a nucleus to break it apart into its individual nucleons

Nuclear Energy

1. Element is bombarded with neutrons
2. Neutrons are absorbed
3. Nucleus becomes unstable and splits into smaller nuclei, radioactive energy and lone neutrons