An Introduction to Atomic and Nuclear Physics-WWII-Definitions

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absorption spectrum
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a continuous spectrum interrupted by dark bands obsessed when light passing through a substance is absorbed at specific frequencies
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alpha decay
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radioactive decay by emission of an alpha particle
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alpha particle
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the nucleus of a helium atom, consisting of two protons and two neutrons, which is emitted during alpha decay
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antiparticle
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an antimatter particle with the same mass and opposite charge as a corresponding matter particle
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atom
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the basic building block of matter; the smallest particle of an element that retains the chemical properties of that element
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atomic clock
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a timekeeping device that uses the frequency of a specific atomic transition as a standard for measuring time
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atomic mass number
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a number equal to the total number of nucleons in an atom
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atomic number
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a characteristic number for each element, equal to the number of protons in the nucleus of an atom of that element
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atomic spectroscopy
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the process of identifying the elemental makeup of a given sample by analyzing the wavelengths of light it emits or absorbs
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atomic theory
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a scientific theory which states that matter is composed of atoms
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background radiation
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ionizing radiation from naturally occurring sources, such as cosmic rays
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becquerel (Bq)
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the standard unit of radioactivity, equal to one decay per second
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beta decay
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radioactive decay by emission of an electron or positron
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beta particle
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term for an electron or positron emitted as a result of beta decay
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binding energy
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the energy required to split a nucleus apart into its component nucleons
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blackbody
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an idealized physical body that absorbs all radiation incident upon it
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Bohr radius
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a physical constant equal to the most probable distance between the electron and the nucleus in the ground state of hydrogen
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Bose-Einstein condensate
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a state of matter in which a collection of bosons is cooled to very nearly absolute zero, at which point a large fraction of the bosons occupy the lowest energy (i.e., ground) quantum state
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boson
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any particle with integer spin, including photons; bosons do not obey the Pauli exclusion principle
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break-even
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the point at which the energy output from a fusion reactor equals the energy input to heat the plasma
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breeder reactor
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a nuclear fission reactor that produces more nuclear fuel than it takes in, while generating power
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bubble chamber
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a device for visualizing the path of radiation as a trial of bubbles in a superheated liquid
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cathode ray
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a beam of electrons observed when an electric voltage is placed across a vacuum tube
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chain reaction
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a self-sustaining series of reactions that tends to be accompanied by a large release of energy
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cloud chamber
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a particle detector in which ionizing radiation passing through a vapor-filled chamber forms a visible trail
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coherent
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describes waves that are in-phase; that is, the peaks of each wave are aligned with one another
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corpuscular theory
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a theory, made famous by Isaac Newton, stating that light is made up of a stream of particles
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correspondence principle
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a principle put forward by Niels Bohr which states that the predictions of quantum mechanics should agree with classical (pre-quantum) physics in the limit of large energies
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cosmic rays
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high-energy radiation that originates from outside the Solar System
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critical mass
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the minimum ,mass of fissile material required for a chain reaction to be self-sustaining
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curie (Ci)
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a non-standard unit of radioactivity, equal to 3.7 x 10^10 decays per second
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Curie temperature
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the characteristic temperature of a magnetic material above which its magnetic properties undergo an abrupt change
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cyclotron
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a type of particle accelerator, invented by Ernest Lawrence, that accelerated charged particles along a spiral path
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daughter nucleus
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a nucleus resulting from the radioactive decay of an another (parent) nucleus
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decay chain
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a series of decays that certain radioactive isotopes go through until reaching a stable isotope
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decay constant
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a characteristics quantity of a radioactive isotope that is inversely proportional to its half-life
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decay rate
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the rate at which radioactive isotopes undergo radioactive decay, expressed in the number of decay events per unit time
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decommissioning
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the process of closing a nuclear power plant after it has passed its effective lifetime
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deuterium
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a stable isotope of hydrogen consisting of a proton, a neutron, and an electron
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diamagnetic
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describes materials in which the magnetic moments of individual atoms tend to oppose an externally applied magnetic field
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double-slit interference
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a phenomenon in which a wave passing through two narrow openings is observed to form a pattern of alternating bright and dark fringes on a screen
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electromagnetic spectrum
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the range of all possible electromagnetic radiation, ordered by frequency
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electron
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a negatively charged subatomic particle that exists outside the nucleus of the atom
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electron capture
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a decay process by which a nucleus absorbs an electron from the atomic cloud, thereby converting a proton into a neutron
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electron volt (eV)
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a unit of energy equal to 1.6 x 10^-19 joules, used to quantify energy transfers on the atomic scale
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emission spectrum
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bands of light at specific frequencies, emitted by a source of electromagnetic radiation
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endothermic reaction
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a reaction that requires an input of energy in order to take place
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energy level
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one of several discrete values for energy that a quantum system can have
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enrichment
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the process of increasing the fraction of a fissile isotope within a sample so that it can sustain a nuclear chain reaction
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excited state
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any state of an atom that is higher in energy than its lowest (ground) state
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exothermic reaction
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a reaction that results in a net release of energy
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exponential decay
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a mathematical relationship describing a quantity that decreases at a rate proportional to how much is remaining
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fermion
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any particle with half-integer spin, including electrons; all fermions obey that Pauli exclusion principle
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ferromagnetic
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describes materials in which the magnetic spins of nearby atoms tend to align with one another, resulting in a permanent magnet
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fissile
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describes a material that will undergo fission upon collision with slow neutrons
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fission products
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the largest “fragments” of nucleus resulting from a fission reaction
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frequency
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the number of oscillations per unit time of a wave or other repeating event
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fusion ignition
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the point at which a nuclear fusion reaction becomes self-sustaining
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gamma decay
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radioactive decay bt emission of a gamma ray
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gamma ray
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extremely high frequency electromagnetic radiation
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Geiger counter
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a device for detecting the presence of ionizing radiation using a gas-filled chamber surrounding a charged wire
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ground state
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the lowest possible energy state of an atom
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half-life
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the time required for half of the radioactive atoms in a given sample to undergo decay
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Heisenberg uncertainty principle
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a quantum mechanical principle stating that the position and momentum of a particle cannot both be precisely known at the same time
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induced radioactivity
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the initiation of a radioactive decay process through artificial means, such as particle bombardment
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ionization energy
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the energy required to completely remove the outermost electron from an atom
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ionizing radiation
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any form of radiation with enough energy to remove electrons from atoms
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isotopes
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atoms with the same number of protons but a different number of neutrons
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laser
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a device that emits a beam of monochromatic, coherent light; laser is an acronym for “light amplification of stimulated emission of radiation”
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laser cooling
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the technique of slowing atoms using specially tuned laser light
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magnetic moment
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a measure of an object’s tendency to align with a magnetic field
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meltdown
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an informal term for overheating of a nuclear reactor, resulting in severe damage to the reactor core
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moderator
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a substance that surrounds the nuclear fuel in a reactor and slows emitted neutrons in order to make them more likely to be absorbed and thus initiate subsequent fission reactions
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neutrino
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an electrically neutral particle with an extremely small mass that tends to pass straight through ordinary matter
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neutron
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an electrically neutral particle located in the nucleus of the atom
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neutron number
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the number of neutrons in the nucleus of an atom
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nuclear fission
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a nuclear reaction in which a heavy nucleus splits into two lighter nuclei
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nuclear force
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a short-range attractive force between protons and neutrons in the nucleus
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nuclear fusion
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a nuclear reaction in which two light nuclei combine to form a heavier nucleus
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nuclear physics
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the branch of physics concerned with the properties and structure of the atomic nucleus
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nuclear reaction
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a process in which two nuclei collide and recombine to form entirely different nuclei
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nuclear reactor
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a device for generating and controlling nuclear chain reactions
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nucleon
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a particle that exists in the nucleus of the atom; includes protons and neutrons
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nucleus
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the positively charged central “core” of an atom, which contains both protons and neutrons and makes up most of an atom’s mass
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paramagnetic
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describes materials in which the magnetic moments of individual atoms tend to align with an externally applied magnetic field, but which become demagnetized when the field is removed
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parent nucleus
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the original nucleus that transforms as a result of radioactive decay
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Pauli exclusion principle
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a quantum mechanical principle stating that two identical fermions cannot occupy the same quantum state; equivalently, no two fermions can have the same set of values for their quantum numbers
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photoelectric effect
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the emission of electrons from the surface of a material when it is illuminated with light of certain frequencies
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photon
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a quantum of electromagnetic radiation that has energy proportional to its frequency
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Planck’s constant
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a fundamental constant of quantum mechanics, equal to 6.63 x 10^-34 J.s
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plasma
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a state of matter composed of free electrons and positively charged ions
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population inversion
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a necessary condition for laser operation, in which more members of a collection of atoms are in an excited state than are in lower energy states
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positron
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the antiparticle of the electron
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probability density
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the probability per unit volume of being detected within a given volume at a given instant
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proton
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a positively charged particle located in the nucleus of the atom
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proton-proton chain
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a series of nuclear fusion reactions in many stars, including the Sun, that gradually convert hydrogen into helium while producing energy
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Q value
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a characteristic value of a nuclear reaction, equal to the difference in mass between the parent nucleus and daughter nuclei
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quantum
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a discrete unit of energy
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quantum mechanics
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the branch of physics concerned with the probabilistic nature of the world at the subatomic scale
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quantum numbers
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a set of values that uniquely describe a quantum state
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quantum theory
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a theory developed in the early twentieth century to describe the world at scales smaller than the atom; precursor to quantum mechanics
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quantum tunneling
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a phenomenon in which the wave properties of matter allow a particle to exist in a region where it would otherwise be forbidden according to classical mechanics
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radiation therapy
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the medical use of radiation to kill harmful cells, such as cancerous tumors
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radioactive
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describes any material that spontaneously undergoes radioactive decay
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radioactive decay
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the process by which an unstable nucleus changes its form by emitting radiation
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radioactivity
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see radioactive decay; can also refer to the rate of decay
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radiometric dating
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a technique for estimating the age of a material by comparing the decay rates of radioactive isotopes it contains with known decay rates
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relative atomic mass
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the average atomic mass of an element, weighted by occurrence in nature, which is often included on periodic tables
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Rydberg formula
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a formula that describes the wavelengths of light within emission spectra of various elements
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scintillation counter
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a device for detecting and measuring ionizing radiation by allowing it to excite a scintillator material
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sievert (Sv)
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a unit of effective dose of ionizing radiation
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stimulated emission
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the process in which an incoming photon causes an excited atom to drop to a lower energy level, thereby emitting a photon in the same direction as the incident photon
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thermonuclear fusion
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the means of achieving nuclear fusion using extremely high temperatures
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threshold energy
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the minimum energy required to initiate an endothermic reaction
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tokamak
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a doughnut-shaped device for containing a plasma using overlapping magnetic fields
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tritium
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a radioactive isotope of hydrogen consisting of a proton, two neutrons, and an electron
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ultraviolet catastrophe
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the contradiction between the classical model of blackbody radiation with experimental results in the early twentieth century; resolved by the Planck hypothesis
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wave function
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a mathematical function that contains all information about a quantum state of one or more particles
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wave-partite duality
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the observation that quantum-scale objects such as subatomic particles exhibit properties of both particles and waves
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wavelength
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the distance between successive points on a wave (e.g., the distance between consecutive peaks)
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X-rays
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electromagnetic radiation with wavelengths between 0.1 and 10 nanometers; X-rays are more energetic that gamma rays
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Zeeman effect
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the splitting of atomic energy levels when an external magnetic field is applied

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