Understanding the strong nuclear force led to the discovery of subatomic particles, requiring the reconciliation of quantum mechanics and special relativity.
Nuclear and radiation physics explain phenomena from smoke detectors to star evolution.
Atomic Number (Z)
Z is the number of protons in the nucleus.
In a neutral atom, the number of protons equals the number of electrons.
Electron configuration determines chemical properties, thus chemical properties depend on Z.
Elements are defined by Z.
Atomic Mass Number (A)
A is the total number of protons and neutrons (nucleons).
An element X is written as ^A_Z X for example \ _{92}^{235}U
Definitions
Nucleon: A nuclear constituent (proton or neutron).
Nuclide: A nucleus or atom with a specific nuclear makeup.
Isotopes: Atoms with the same number of protons but different numbers of neutrons.
Isotones: Atoms with the same number of neutrons but different numbers of protons.
Isobars: Atoms with the same number of nucleons but different numbers of protons.
Isomers: Atoms with the same number of protons and neutrons but different nuclear energy states (e.g., \ ^{m}Xe).
Atomic Mass Unit (amu)
Defined such that the atomic mass of Carbon-12 is exactly 12 amu.
Avogadro’s Number is the number of atoms in exactly 0.012 kg of Carbon-12.
1 \text{ amu} = 1.66 \times 10^{-27} \text{ kg}.
Energy Equivalent of Mass
Using E = mc^2, 1 \text{ amu} = 931.494 \text{ MeV}.
Strong Nuclear Force
Short-range attractive force between nucleons; holds the nucleus together.
The strongest of all forces, approximately 100 times stronger than electrostatic forces.
Overcomes electrostatic repulsion between protons.
Binding Energy
The mass of an atom's constituents is greater than the mass of the atom itself.
Mass defect (\Delta m): The difference between the mass of the atom and its constituent parts.
Binding energy is the energy required to break the atom into its constituents.
Greater binding energy implies a more stable atom.
Stability Diagram (Segrè Chart)
Graph of neutron number (N) vs. proton number (Z).
Stable nuclei reside within a band; larger nuclei require more neutrons to overcome proton repulsion.
Nuclear Reactions
Nuclear Decay
Nuclear Fusion: Joining smaller nuclei to form larger nuclei (mass number < 56).
Requires extremely high temperatures ($\sim 10^9 \text{ K}$).
Nuclear Fission: Breaking up larger nuclei to form smaller nuclei (mass number > 56).