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Modern Physics

Definitions

TermDefinition
Electron Indivisible quantity of charge that orbits the nucleus of an atom
Thermionic Emission Emission of electrons from the surface of a hot metal
Work Function Minimum energy needed to remove the loosest electrons from the surface of a metal
X-rays Electromagnetic radiation of extremely high frequency and short wavelength
Photoelectric Effect Emission of electrons from the surface of a metal due to electromagnetic radiation of a suitable frequency hitting the metal
Photon Bundle of light energy
Threshold Frequency Minimum frequency needed to cause photoelectric emission
Protons Positively charged nucleons, with the same size charge as the electron
Neutrons Electrically neutral nucleons, with slightly larger mass than protons
Atomic Number Number of protons in the nucleus of an atom
Mass Number Number of protons plus neutrons in the nucleus of an atom
Isotopes Atoms of the same atomic number but different mass number
Radioactivity Spontaneous emission of radiation due to the natural disintegration of an unstable nucleus
Ionisation The charging of a neutral atom or molecule when it loses or gains one or more electrons
Penetration Distance that radiation travels through a medium
Radioisotope An unstable isotope of an element that decays spontaneously emitting radiation
Alpha Emission The emission of a helium nucleus from a large atom
Beta Emission The emission of an electron when a neutron decays into a proton
Gamma Emission The emission of high energy photons from an unstable nucleus
Radioactive Activity The rate of emissions from a radioactive source
Half-life Time taken for half of the nuclei in a given sample of radioactive isotope to decay
Nuclear Fission The splitting of a large nucleus into two smaller nuclei of roughly equal mass, with emission of neutrons and release of energy
Nuclear Fusion The combining of two small nuclei to form a single larger nucleus, with the release of energy
Chain Reactions Where at least one neutron is released during each fission reaction
Critical Mass Minimum amount of fissile material needed in order for chain reactions to occur
Radiation Emission of particles of matter or photons of energy
Background Radiation Radiation that comes from environmental sources including the Earth's crust, the atmosphere, cosmic rays and radioisotopes
Created by: conordesmond