PROTONS Elementary particles with a single positive electrical charge and a mass approximately 1837 times that of the electron. The atomic number of an atom is equal to the number of protons in its nucleus.
RADIOACTIVE DECAY The change of one nuclide to another by the emission of charged particles from the nucleus of its atom.
RADIOACTIVITY The property of some nuclides to decay by themselves into others.
RADIOGENIC Formed as the result of radioactive decay.
RARE EARTH Any of the elements from atomic number 57 (lanthanum) to 71 (lutetium).
SAMPLE COUNTER An instrument into which a sample of material can be placed to have its radiation measured.
SECULAR EQUILIBRIUM The production of a radioactive substance at a rate equal to its decay.
SPECIFIC ACTIVITY The number of atoms decaying per unit time per unit weight of the total amount being tested.
SPIKE A known amount of an element of unusual isotopic composition used in isotope-dilution analysis.
STATISTICAL ERROR The error associated with nuclear measurements and arising from the random distribution of nuclear events.