Key Terms

alpha (α) decay

loss of an alpha particle during radioactive decay

alpha particle

(α or ${}_{\mathbf{2}}^{\mathbf{4}}\mathbf{\text{He}}$ or ${}_{\mathbf{2}}^{\mathbf{4}}\mathbf{\text{α}})$ high-energy helium nucleus; a helium atom that has lost two electrons and contains two protons and two neutrons

antimatter

particles 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) decay

breakdown of a neutron into a proton, which remains in the nucleus, and an electron, which is emitted as a beta particle

beta particle

$\mathbf{\text{(β}}$ or ${}_{\mathbf{-1}}^{\mathbf{0}}\mathbf{\text{e}}$ or ${}_{\mathbf{-1}}^{\mathbf{0}}\mathbf{\text{β}}\mathbf{\text{)}}$ high-energy electron

binding energy per nucleon

total binding energy for the nucleus divided by the number of nucleons in the nucleus

chain reaction

repeated fission caused when the neutrons released in fission bombard other atoms

chemotherapy

similar 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 rod

material inserted into the fuel assembly that absorbs neutrons and can be raised or lowered to adjust the rate of a fission reaction

critical mass

amount 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 $\times$ 10¹⁰ disintegrations/s

daughter nuclide

nuclide produced by the radioactive decay of another nuclide; may be stable or may decay further

electron capture

combination 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 therapy

radiation delivered by a machine outside the body

fissile (or fissionable)

when a material is capable of sustaining a nuclear fission reaction

fission

splitting of a heavier nucleus into two or more lighter nuclei, usually accompanied by the conversion of mass into large amounts of energy

fusion

combination of very light nuclei into heavier nuclei, accompanied by the conversion of mass into large amounts of energy

fusion reactor

nuclear reactor in which fusion reactions of light nuclei are controlled

gamma (γ) emission

decay of an excited-state nuclide accompanied by emission of a gamma ray

gamma ray

(γ or ${}_{\mathbf{0}}^{\mathbf{0}}\mathbf{\text{γ}}\mathbf{\text{)}}$ short wavelength, high-energy electromagnetic radiation that exhibits wave-particle duality

Geiger counter

instrument 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 (t_1/2)

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 radiation

radiation that can cause a molecule to lose an electron and form an ion

magic number

nuclei with specific numbers of nucleons that are within the band of stability

mass defect

difference 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 equation

Albert 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 $\times$ 10¹⁰ disintegrations/s

nonionizing radiation

radiation 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 energy

energy lost when an atom’s nucleons are bound together (or the energy needed to break a nucleus into its constituent protons and neutrons)

nuclear chemistry

study of the structure of atomic nuclei and processes that change nuclear structure

nuclear fuel

fissionable isotope present in sufficient quantities to provide a self-sustaining chain reaction in a nuclear reactor

nuclear moderator

substance that slows neutrons to a speed low enough to cause fission

nuclear reaction

change to a nucleus resulting in changes in the atomic number, mass number, or energy state

nuclear reactor

environment that produces energy via nuclear fission in which the chain reaction is controlled and sustained without explosion

nuclear transmutation

conversion of one nuclide into another nuclide

nucleon

collective term for protons and neutrons in a nucleus

nuclide

nucleus of a particular isotope

parent nuclide

unstable nuclide that changes spontaneously into another (daughter) nuclide

particle accelerator

device that uses electric and magnetic fields to increase the kinetic energy of nuclei used in transmutation reactions

positron $\text{(}{}_{\mathrm{+1}}^0\text{β}$ or ${}_{\mathrm{+1}}^0\text{e}\text{)}$

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 dosimeter

device that measures ionizing radiation and is used to determine personal radiation exposure

radiation therapy

use of high-energy radiation to damage the DNA of cancer cells, which kills them or keeps them from dividing

radioactive decay

spontaneous decay of an unstable nuclide into another nuclide

radioactive decay series

chains 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

radioactivity

phenomenon 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 dating

highly accurate means of dating objects 30,000–50,000 years old that were derived from once-living matter; achieved by calculating the ratio of ${}_6^{14}\text{C}\text{:}{}_6^{12}\text{C}$ in the object vs. the ratio of ${}_6^{14}\text{C}\text{:}{}_6^{12}\text{C}$ in the present-day atmosphere

radioisotope

isotope that is unstable and undergoes conversion into a different, more stable isotope

radiometric dating

use of radioisotopes and their properties to date the formation of objects such as archeological artifacts, formerly living organisms, or geological formations

reactor coolant

assembly 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 counter

instrument 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 force

force of attraction between nucleons that holds a nucleus together

subcritical mass

amount of fissionable material that cannot sustain a chain reaction; less than a critical mass

supercritical mass

amount of material in which there is an increasing rate of fission

transmutation reaction

bombardment of one type of nuclei with other nuclei or neutrons

transuranium element

element with an atomic number greater than 92; these elements do not occur in nature