Definitions

Alpha Decay

• Definition: Alpha decay is a type of radioactive decay where an unstable nucleus releases an alpha particle, which consists of two protons and two neutrons. This process reduces the mass and atomic number of the original nucleus, making it more stable.

Annihilation

• Definition: Annihilation occurs when a particle collides with its antiparticle. This collision converts their combined mass into energy, typically released as two gamma photons. The energy released is in line with Einstein's E = mc² principle.

Antiparticle

• Definition: Every particle has a corresponding antiparticle that shares the same mass but has opposite charge and other opposite properties, such as baryon and lepton numbers.

Baryon Number

• Definition: A conserved quantum number representing the number of baryons (heavy particles) in a system. Baryons have a baryon number of +1, while antibaryons have -1. This number remains unchanged in particle interactions.

Baryons

• Definition: Baryons are a group of hadrons made up of three quarks. The proton is the only stable baryon, while the neutron, also a baryon, is stable only within a nucleus.

Beta Decay

• Beta-Minus Decay: A neutron in a nucleus converts into a proton, emitting an electron (beta particle) and an antineutrino.
• Beta-Plus Decay: A proton converts into a neutron, emitting a positron and a neutrino. This type of decay is common in proton-rich nuclei.

Electron Diffraction

• Definition: When electrons pass through a small gap comparable to their de Broglie wavelength, they exhibit wave-like properties, spreading out in a pattern.
• Significance: Electron diffraction is evidence of wave-particle duality in electrons, supporting the idea that particles can behave as waves under certain conditions.

Electron Volt (eV)

• Definition: An electron volt (eV) is the energy gained by an electron when it is accelerated through a potential difference of 1 volt. 1 eV is equal to 1.6 × 10⁻¹⁹ joules.
• Application: The electron volt is a convenient unit of energy, particularly in atomic and nuclear physics, due to the small energies involved.

Energy Levels

• Definition: Electrons within an atom exist at specific energy levels or shells. Electrons cannot exist in-between these levels.

Excitation

• Definition: Excitation occurs when an electron absorbs exactly the right amount of energy to move to a higher energy level within an atom.

Gauge Boson

• Definition: Gauge bosons are particles that mediate the four fundamental forces. Each force has its corresponding boson: photons for electromagnetism, W and Z bosons for the weak force, gluons for the strong force, and gravitons (hypothetical) for gravity.

Ground State

• Definition: The ground state is the lowest energy level that an electron can occupy in an atom. It is the most stable state.
• Importance: Electrons in higher energy levels naturally return to the ground state, releasing energy as they do so.

Hadrons

• Definition: Hadrons are particles that are subject to the strong nuclear force and are composed of quarks. There are two main categories:
  • Baryons (three quarks), such as protons and neutrons.
  • Mesons (quark-antiquark pairs), like pions and kaons.

Ionisation

• Definition: Ionisation is the process where an atom loses or gains an electron, becoming a charged ion.

Isotope

• Definition: Isotopes are atoms of the same element with the same proton number but different neutron numbers.

Pair Production

• Definition: Pair production occurs when a high-energy photon is converted into a particle-antiparticle pair (such as an electron and a positron) near a nucleus.

Photon

• Definition: A photon is a quantum of electromagnetic radiation and acts as a particle of light.
• Energy: Given by E = hf, where h is Planck's constant and f is the frequency of the radiation.

Strange Particles and Strangeness

• Definition: Strange particles are created through the strong interaction but decay via the weak interaction.
• Strangeness: A quantum number conserved in strong interactions but can change in weak interactions, reflecting that strange particles are typically produced in pairs.

Strong Nuclear Force

• Definition: This is the fundamental force that binds protons and neutrons within the nucleus, overcoming the electromagnetic repulsion between protons.
• Range: It acts attractively up to about 3 femtometres (fm) and becomes repulsive below 0.5 fm to prevent the collapse of nucleons.

Threshold Frequency

• Definition: The minimum frequency of light required to release electrons from a metal's surface through the photoelectric effect.
• Relation to Work Function: Threshold frequency is calculated as f_min = φ/h, where φ is the work function, and h is Planck's constant.

Work Function

• Definition: The work function is the minimum energy needed to release an electron from a metal surface.
• Application: In the photoelectric effect, only photons with energy equal to or greater than the work function can eject electrons.