Nuclear Fission and Fusion: Unit IV: Atomic Physics Welter Class Notes
Nuclear Fission and Fusion: Unit IV: Atomic Physics Welter Class Notes
Nuclear Fission and Fusion: Unit IV: Atomic Physics Welter Class Notes
The mass of the nucleus is actually about 1% smaller than the mass of its
individual protons and neutrons. This difference is called the mass defect.
The mass defect results from the energy released when the protons and neutrons
bind together to form the nucleus. This energy is called the nuclear binding
energy.
The binding energy determines which nuclei are stable and how much energy is
released in a nuclear reaction. The higher the binding energy, the more stable the
nucleus.
Very heavy nuclei and very light nuclei have low binding energies. This implies:
1. a heavy nucleus will release energy when it splits apart (what we call
fission)
2. two light nuclei will release energy when they join (what we call fusion).
The mass defect and binding energy are
related by Albert Einstein's formula, E =
mc2 which shows that matter and
energy are interchangeable.
This equation is key to the power of nuclear weapons and nuclear reactors.
Nuclear Fission
Very large nuclei (mass number greater than 230) tend to be unstable and can
split into two or more parts. This is called fission.
Fission is not a spontaneous process. It can only occur when a slow moving
neutron strikes an unstable nucleus.
In this decay process, the nucleus will split into two nearly equal nuclei and
release several free neutrons and huge amounts of energy.
These nuclei are isotopes of more stable elements. If left alone, they decay
radioactively by emitting alpha or beta particles.
If these neutrons are absorbed by other nuclei, this causes a chain reaction.
Notice:
The mass numbers balance (235 + 1 = 90 + 143 + 3).
Solution:
Nuclear Fusion
Very light nuclei can combine to form heavier atoms in a process known as
fusion.
When fusion happens, the products have a larger binding energy than
the reactants. The mass defect results in the release of huge amounts of
energy.
Actually produces more energy per gram of products than fission and
produces no by-products