Fission and Fusion

• Nuclear fission & fusion are nuclear reactions that change the nucleus of an atom to produce high amounts of energy from the energy stored in the nucleus of an atom
• Nuclear fission is defined as the splitting of a large, unstable nucleus into two smaller nuclei
• During fission:

  • A neutron collides with an unstable nucleus
  • The neutron and the nucleus are the reactants
  • The nucleus splits into two smaller nuclei (called daughter nuclei) and two or three neutrons
  • The daughter nuclei and the neutrons are the products of the reaction
  • Gamma rays are also emitted
• Nuclear fission process

  • A neutron is fired into the target nucleus, causing it to split

  A) neutron

  B) target nucleus

  C) neutron

  D) fission product

  E) neutron

  F) fission product

  G) neutron

  
• • An example of a nuclide equation for the fission of uranium-235 is:
  • Where:
  • U is an unstable isotope of uranium
  • n is a neutron
  • Kr is an unstable isotope of krypton
  • Ba is an unstable isotope of barium
• Nuclear fission of uranium-235

  • Large nuclei can decay by fission to produce smaller nuclei and neutrons with a lot of kinetic energy

  A) neutron

  B) uranium

  C) 235

  D) daughter nuclei

  E) 2 or 3 neutrons

  
• Energy is conserved in a nuclear fission reaction
• In the example:

  A) sum

  B) nucleon

  C) reactants

  D) equal

  E) sum

  F) nucleon

  G) products

  H) proton

  
• The products of fission move away very quickly

  • During a fission reaction, energy is transferred from nuclear energy store of the parent nucleus to the kinetic energy store of the reactants
• The mass of the products is less than the mass of the original nucleus

  • This is because the remaining mass has been converted into energy, which is released during the fission process
• Large isotopes with a large nucleon number, such as uranium and plutonium, both undergo fission and are used as fuels in nuclear power stations
• Nuclear fusion is defined as when two light nuclei join to form a heavier nucleus
• Stars use nuclear fusion to produce energy

  • In most stars, hydrogen nuclei (light nuclei) are fused together to form a helium nucleus (heavier nucleus) and massive amounts of energy is produced
• Nuclear fusion of hydrogen

  A) energy

  
• Nuclear fusion requires extremely high temperature and pressure

  • So fusion is very hard to reproduce on Earth
• An example of a nuclide equation for fusion is:

  • Where:
  • 2H1is deuterium (isotope of hydrogen with 1 proton and 1 neutron)
  • 1H1 is hydrogen (with one proton)
  • 3He2 is an isotope of helium (with two protons and one neutron)

  
• The energy produced during nuclear fusion comes from a very small amount of a particle’s mass converted into energy

  • Therefore, the mass of the product (fused nucleus) is less than the mass of the two original nuclei (reactants)
  • The remaining mass has been converted into the energy released when the nuclei fuse
• The amount of energy released during nuclear fusion is huge:

  • The energy from 1 kg of hydrogen that undergoes fusion is equivalent to the energy from burning about 10 million kilograms of coal