Particles

Particle Zoo

Leptons

Fundamental particles

E.g: Electron, muon, neutrino

Particle Forces

There are 4 fundamental forces in the universe, each mediated by an exchange particle, whose role it is to carry the force between the particles

Neutrino and Antineutrino

These leptons must exist to account for other particles from interactions having a range of possible energies-

Strong Nuclear Force

Responsible or keeping nucleons together in a nucleus

When this strong force is in balance with the repulsive EM force between protons, the nucleus is stable

Conservation Rules

Charge Q, Baryon number B and Lepton number L must all be conserved in any interaction

Alpha Decay

Occurs in larger nuclei

Nucleus ejects Helium nucleus (2 protons + 2 neutrons)

Larger nuclei → Helium Nucleus + Smaller Nuclei

Beta Decay

Occurs in smaller nuclei

A neutron decays into a proton + electron

• Gains proton, but mass is unchanged

Annihalation

The result of a particle and its respective antiparticle meeting. All mass is converted to energy in the form of two photons

Einstein’s Theory of relativity

E = mc²

E = rest energy (J)

m = mass (kg)

c = speed of light (3.0 × 10⁸ ms^-1)

Minimum Energy of photons

2mc² = 2hf

Pair Production

When a photon of sufficient energy is converted to its particle and antiparticle

Minimum frequency of photon required or pair production

hf = 2mc²

Energy levels

Specific, discrete levels of energy that electrons can take

Electrons can be excited to higher energy levels by

• Colliding with a free electron

• Absorbing a photon of energy equal to the difference in energy (all others will pass through)

De-excitation

When an electron drops in energy level back to the ground state, emitting photons.

Since E = hf = hc/λ, the bigger the drop in energy, the higher the frequency and the shorter the wavelength

If the incoming photon or free electron has enough energy, the electron can reach the ionisation level, causing it to leave the atom, leaving behind a positive ion

Electronvolt

1 eV = 1.6×10^-19J