DECAY CONSTANT The number of atoms decaying per atom per unit of time (0.693/half-life).
ELECTRON CAPTURE A nuclear process in which the nucleus of an atom captures an electron from one of the inner shells.
ELECTRONS Elementary particles with a unit negative electrical charge and a mass 1/1837 that of the proton, or 9.12 × 10⁻²⁷ gram. Electrons surround the atom’s positively charged nucleus and determine the atom’s chemical properties.
GAMMA RAYS Electromagnetic radiation from an atomic nucleus.
GEIGER COUNTERS Instruments that count pulses produced by radioactivity, consisting of a counting tube with a central wire anode, usually filled with a mixture of argon and organic vapor.
HALF-LIFE The time it takes for half the atoms in a radioactive substance to decay.
ION An atom or molecule that has lost or gained one or more electrons and is thus electrically charged.
ISOTOPE DILUTION An analytical technique involving addition of a known amount of an isotopic mixture of abnormal composition to the unknown amount of an element of normal or known isotopic composition.
ISOTOPES Nuclides of the same atomic number but different atomic weight. Isotopes of a given element have an identical number of protons but different numbers of neutrons in their nuclei.
LAW OF SUPERPOSITION Statement that overlying strata must be younger than underlying strata if there has been no inversion.