Nuclear and Particle Physics: Atomic Structure

Atomic Structure

Fundamental Particles

Particles that make up matter are called fundamental particles.
These include: quarks, leptons, and exchange particles.
Quarks are included in particles called hadrons. There are six types of quarks: up, down, charm, strange, top, and bottom.
Leptons are fundamental particles not made up of quarks. This includes electrons, muons, tau particles, and their associated neutrinos.
Exchange particles, also known as gauge bosons, mediate the four fundamental forces: The photon (electromagnetic), W and Z bosons (weak nuclear), gluon (strong nuclear), and graviton (gravity).

An atom consists of a central nucleus and surrounding electron cloud.
The nucleus consists of protons (with a +1 charge) and neutrons (no charge).
Electrons occupy energy levels or shells around the nucleus. They are much lighter than protons or neutrons and carry a -1 charge.

The atomic number, or proton number (Z), defines the element and gives the number of protons in the nucleus.
The mass number (A) is the total number of nucleons (protons and neutrons combined) in the nucleus.
Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons.

Some atomic nuclei are unstable and emit particles and/or radiation - this property is known as radioactivity.
Types of radioactive decay include alpha (α) decay, beta (β) decay, and gamma (γ) emission.
Balance of equations - the overall charge and nucleon number must be conserved in radioactive decay equations.

The strong nuclear force binds the nucleons together in the nucleus, overcoming the electrostatic repulsion between protons.
The range of the strong nuclear force is very short and it is essentially zero beyond about 10-15 m.
The weak nuclear force is responsible for radioactive decay or beta decay.

Nucleon separation - nucleons are spaced evenly within the nucleus; it’s not an atom with a ‘solid’ nucleus.
Charge distribution - the positive charge of the nucleus is distributed evenly throughout.
The radius of the nucleus (R) is proportional to the cube root of the mass number (A) of the nucleus. The size of the nucleus increases as the number of nucleons increases.

For every particle, there is a corresponding antiparticle with the same mass but opposite charge. For example, the positron is the antiparticle of the electron.
When a particle encounters its antiparticle, an annihilation reaction happens, producing energy in the form of photons.