# Quantum and Nuclear Physics Vocabulary Paula Corcoran
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Photoelectric effect

The observation that metals and other materials emit electrons when light (photons) are incident upon them
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Threshold frequency

The minimum frequency that photons may have to emit an electron when incident on a specific surface
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Work function

The energy required (by the photon) to overcome the attractive forces the electrons contain within the metal
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Photoelectron

The electron that has been emitted from a surface due to the incidence of photons
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Wave-particle duality

The phenomena in which light appears to have some characteristics of both waves and particles
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The de Broglie wavelength

The necessary wavelength for a specific particle of matter to exhibit wave-like characteristics
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The Bohr Model

The model of the atom in which electrons can only occupy orbits of specific radii. It contains the following assumptions: 1) Electrons in an atom exist in stationary states 2) Electrons may move from one stationary state to the next by absorbing or emitting a quantum of electromagnetic radiation 3) The angular momentum of an electron in a stationary state is quantized in integral values of h/2π
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Quantum mechanics

The mathematical description of the motion and interaction of subatomic particles, incorporating the concepts of quantization of energy, wave-particle duality, the uncertainty principle, and the correspondence principle.
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Schrödinger’s wave function

A theoretical value that has no meaning on its own. However, the square of its magnitude is proportional to probability per unit volume of finding the particle (probability density)
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The Copenhagen Interpretation

An expression or meaning of quantum mechanics that is summarized as “nothing is real unless it is observed.” The wave function collapses as it is observed and returns to the classical case and the particle is detected.
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Pair production

When a photon (containing the right energy close to a nucleus) turns into a particle and its antiparticle pair. The minimum energy to do this is given by E = 2mc^2
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Pair annihilation

When a particle meets its antiparticle and annihilate each other resulting in 2 photons. The total energy of the photons is equal to the total mass-energy of the annihilating particles.
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Quantum tunneling

The quantum mechanical phenomenon where a particle tunnels through a barrier that it classically could not surmount. The wave function indicates that there is a small probability of the particle being anywhere in the universe at the same time.
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Unified atomic mass unit

One-twelfth of the rest mass of an unbound atom of carbon-12 in its nuclear and electronic ground state
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Gravitational force

A weak force that has infinite range and acts on all particles. It is always attractive and over astronomical distances it is the dominant force while on an atomic or subatomic scale it is negligible
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Electromagnetic force

A force that electric and magnetic effects over infinite distances. It is much stronger at shorter distances and has either attractive or repulsive effects and acts on all charged particles
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Strong nuclear force

A very strong force that acts on hadrons (quarks, nucleons) but has very short range.
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Weak nuclear force

The force that is responsible for radioactive decay and neutrino interactions. It acts over very small distances and on all particles.
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Standard model

A mathematical description of the elementary particles of matter and the electromagnetic, weak, and strong forces by which they interact.
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Half-life

The time taken for half of the total number of nuclei initially in the sample to decay (or the initial activity of a sample to fall by half)
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Background count

The background radiation detected in a given area in a Geiger counter
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Zone of stability

The pattern that is formed when a graph of the variation of the neutron number and proton number for a stable nuclei is made
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Binding energy

The energy required to dismantle a nucleus into all of its constituent nucleons and overcome the strong nuclear force acting between them
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Mass defect

The loss of mass due to the energy required to form the nucleus from its individual parts. (The total mass of the individual nucleons making up a nucleus must be greater than the mass of that nucleus)
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Nuclear fusion

The joining together of small nuclei to give larger ones
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Nuclear fission

The breaking of larger nuclei into smaller ones
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Positron

The antiparticle of the electron
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Leptons

Particles that are members of the electron family and consist of the electron, the muon, and the tau, their antiparticles plus three neutrinos associated with each of the particles and three neutrinos associated with each of the antiparticles
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Quarks

Any of a number of subatomic particles carrying a fractional electric charge, postulated as building blocks of the hadrons
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