Glossary

Accuracy The closeness of a measurement to its true value. b-decay A form of ionizing radiation released by certain radioactive materials, consisting of high-energy

Electrons or positrons designated by the symbols p— and b+, respectively.

G-ray An energetic form of electromagnetic radiation equivalent to a high-speed photon produced by radioactive decay; denoted by the Greek letter g.

Half-life The length of time required for one-half of the initial activity of a radioisotope to decay; after one half-life, 50% of the original activity remains; after two half-lives, only 25% of the original activity remains.

Isotope Any of several different forms of an element with different atomic mass; isotopes of an element will have nuclei

Box 1 Elements and Isotopes

An element Xis defined by its atomic number Z(which represents the number of protons) and by its mass number A (which represents the sum of its protons and neutrons). An element can be designated as A X although Z is redundant with the chemical symbol X and is generally omitted. Electrons, arranged in a series of shells surrounding the nucleus, are equal in number to Z.

Isotopes of an element have the same number of protons, but different number of neutrons, i. e., same Z but different A. A few elements are ‘mono-isotopic’, that is, having only one natural isotope. Most elements, however, have more than one naturally occurring isotope, in which case the relative fractional abundance of the isotopes is generally constant or fixed.

For example, aluminum is mono-isotopic; all naturally occurring aluminum is 27Al.

In contrast, iron has four naturally occurring stable isotopes with the following abundances:

During irradiation, each isotope undergoes a distinct reaction and subsequent decay, and yields gamma rays characteristic of the specific isotope. Since most isotopic ratios are assumed to be constant (there are some important exceptions), any one isotope can be analyzed to determine the amount of element present.

The terms ‘radioisotope’ and ‘radionuclide’ refer to isotopes which are radioactive. These may be naturally occurring in the environment, or more typically, are created through activation by neutrons.

With the same number of protons but different numbers of neutrons.

Neutron flux The density of neutrons available to irradiate a sample, typically measured in neutrons per cm2 per second.

Precision The closeness of repeated measurements of the same quantity; measurement replicability.

Provenance The geographic origin of an artifact, object, or raw material.

Radioisotope A radioactive isotope of an element; the

Radioisotope may be naturally occurring or artificially produced through irradiation.

Radionuclide An atom with an unstable nucleus which undergoes radioactive decay by emitting a g-ray(s) and/or subatomic particles.

Sensitivity The smallest amount of a chemical or element detectable by an analytical method.