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Chemistry LibreTexts

21.8: Key Terms

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    Example and Directions
    Words (or words that have the same definition)The definition is case sensitive(Optional) Image to display with the definition [Not displayed in Glossary, only in pop-up on pages](Optional) Caption for Image(Optional) External or Internal Link(Optional) Source for Definition
    (Eg. "Genetic, Hereditary, DNA ...")(Eg. "Relating to genes or heredity")The infamous double helix; Delmar Larsen
    Glossary Entries
    alpha (α) decayloss of an alpha particle during radioactive decay    
    alpha particle(α or or high-energy helium nucleus; a helium atom that has lost two electrons and contains two protons and two neutrons    
    antimatterparticles with the same mass but opposite properties (such as charge) of ordinary particles    
    band of stability(also, belt of stability, zone of stability, or valley of stability) region of graph of number of protons versus number of neutrons containing stable (nonradioactive) nuclides    
    becquerel (Bq)SI unit for rate of radioactive decay; 1 Bq = 1 disintegration/s    
    beta (β) decaybreakdown of a neutron into a proton, which remains in the nucleus, and an electron, which is emitted as a beta particle    
    beta particle or or high-energy electron    
    binding energy per nucleontotal binding energy for the nucleus divided by the number of nucleons in the nucleus    
    chain reactionrepeated fission caused when the neutrons released in fission bombard other atoms    
    chemotherapysimilar to internal radiation therapy, but chemical rather than radioactive substances are introduced into the body to kill cancer cells    
    containment system(also, shield) a three-part structure of materials that protects the exterior of a nuclear fission reactor and operating personnel from the high temperatures, pressures, and radiation levels inside the reactor    
    control rodmaterial inserted into the fuel assembly that absorbs neutrons and can be raised or lowered to adjust the rate of a fission reaction    
    critical massamount of fissionable material that will support a self-sustaining (nuclear fission) chain reaction    
    curie (Ci)larger unit for rate of radioactive decay frequently used in medicine; 1 Ci = 3.7 1010 disintegrations/s    
    daughter nuclidenuclide produced by the radioactive decay of another nuclide; may be stable or may decay further    
    electron capturecombination of a core electron with a proton to yield a neutron within the nucleus    
    electron volt (eV)measurement unit of nuclear binding energies, with 1 eV equaling the amount energy due to the moving an electron across an electric potential difference of 1 volt    
    external beam radiation therapyradiation delivered by a machine outside the body    
    fissile (or fissionable)when a material is capable of sustaining a nuclear fission reaction    
    fissionsplitting of a heavier nucleus into two or more lighter nuclei, usually accompanied by the conversion of mass into large amounts of energy    
    fusioncombination of very light nuclei into heavier nuclei, accompanied by the conversion of mass into large amounts of energy    
    fusion reactornuclear reactor in which fusion reactions of light nuclei are controlled    
    gamma (γ) emissiondecay of an excited-state nuclide accompanied by emission of a gamma ray    
    gamma ray(γ or short wavelength, high-energy electromagnetic radiation that exhibits wave-particle duality    
    Geiger counterinstrument that detects and measures radiation via the ionization produced in a Geiger-Müller tube    
    gray (Gy)SI unit for measuring radiation dose; 1 Gy = 1 J absorbed/kg tissue    
    half-life (t1/2)time required for half of the atoms in a radioactive sample to decay    
    internal radiation therapy(also, brachytherapy) radiation from a radioactive substance introduced into the body to kill cancer cells    
    ionizing radiationradiation that can cause a molecule to lose an electron and form an ion    
    magic numbernuclei with specific numbers of nucleons that are within the band of stability    
    mass defectdifference between the mass of an atom and the summed mass of its constituent subatomic particles (or the mass “lost” when nucleons are brought together to form a nucleus)    
    mass-energy equivalence equationAlbert Einstein’s relationship showing that mass and energy are equivalent    
    millicurie (mCi)larger unit for rate of radioactive decay frequently used in medicine; 1 Ci = 3.7 1010 disintegrations/s    
    nonionizing radiationradiation that speeds up the movement of atoms and molecules; it is equivalent to heating a sample, but is not energetic enough to cause the ionization of molecules    
    nuclear binding energyenergy lost when an atom’s nucleons are bound together (or the energy needed to break a nucleus into its constituent protons and neutrons)    
    nuclear chemistrystudy of the structure of atomic nuclei and processes that change nuclear structure    
    nuclear fuelfissionable isotope present in sufficient quantities to provide a self-sustaining chain reaction in a nuclear reactor    
    nuclear moderatorsubstance that slows neutrons to a speed low enough to cause fission    
    nuclear reactionchange to a nucleus resulting in changes in the atomic number, mass number, or energy state    
    nuclear reactorenvironment that produces energy via nuclear fission in which the chain reaction is controlled and sustained without explosion    
    nuclear transmutationconversion of one nuclide into another nuclide    
    nucleoncollective term for protons and neutrons in a nucleus    
    nuclidenucleus of a particular isotope    
    parent nuclideunstable nuclide that changes spontaneously into another (daughter) nuclide    
    particle acceleratordevice that uses electric and magnetic fields to increase the kinetic energy of nuclei used in transmutation reactions    
    positron or antiparticle to the electron; it has identical properties to an electron, except for having the opposite (positive) charge    
    positron emission(also, β+ decay) conversion of a proton into a neutron, which remains in the nucleus, and a positron, which is emitted    
    radiation absorbed dose (rad)SI unit for measuring radiation dose, frequently used in medical applications; 1 rad = 0.01 Gy    
    radiation dosimeterdevice that measures ionizing radiation and is used to determine personal radiation exposure    
    radiation therapyuse of high-energy radiation to damage the DNA of cancer cells, which kills them or keeps them from dividing    
    radioactive decayspontaneous decay of an unstable nuclide into another nuclide    
    radioactive decay serieschains of successive disintegrations (radioactive decays) that ultimately lead to a stable end-product    
    radioactive tracer(also, radioactive label) radioisotope used to track or follow a substance by monitoring its radioactive emissions    
    radioactivityphenomenon exhibited by an unstable nucleon that spontaneously undergoes change into a nucleon that is more stable; an unstable nucleon is said to be radioactive    
    radiocarbon datinghighly accurate means of dating objects 30,000–50,000 years old that were derived from once-living matter; achieved by calculating the ratio of in the object vs. the ratio of in the present-day atmosphere    
    radioisotopeisotope that is unstable and undergoes conversion into a different, more stable isotope    
    radiometric datinguse of radioisotopes and their properties to date the formation of objects such as archeological artifacts, formerly living organisms, or geological formations    
    reactor coolantassembly used to carry the heat produced by fission in a reactor to an external boiler and turbine where it is transformed into electricity    
    relative biological effectiveness (RBE)measure of the relative damage done by radiation    
    roentgen equivalent man (rem)unit for radiation damage, frequently used in medicine; 100 rem = 1 Sv    
    scintillation counterinstrument that uses a scintillator—a material that emits light when excited by ionizing radiation—to detect and measure radiation    
    sievert (Sv)SI unit measuring tissue damage caused by radiation; takes into account energy and biological effects of radiation    
    strong nuclear forceforce of attraction between nucleons that holds a nucleus together    
    subcritical massamount of fissionable material that cannot sustain a chain reaction; less than a critical mass    
    supercritical massamount of material in which there is an increasing rate of fission    
    transmutation reactionbombardment of one type of nuclei with other nuclei or neutrons    
    transuranium elementelement with an atomic number greater than 92; these elements do not occur in nature    

    21.8: Key Terms is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by LibreTexts.

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