Alpha particle: Charged particles emitted from a radioactive atom. Each charged particle consists of two protons and two neutrons.

Atom: This is the smallest unit of an element. It contains a nucleus with neutrons and protons, surrounded by orbiting electrons.

Atomic mass: The mass of an atom usually expressed as atomic mass unit (amu).

Beta particle: (often designated beta rays) Charged particles emitted from a radioactive atom. These particles are identical except for their charge. The charge is classified as positive (positron) or negative (electrons or negatron).

Cathode rays: Electrons originating at the cathodes of gaseous discharge devices. These electrons are often focused in a small area such as a tube and intensified on a surface. The most familiar form of a cathode-ray tube is the television picture tube.

Conductivity: The ratio of electric current to the electric field in a material. Passage of electric charge which can occur a variety of ways such as passage of electrons or ionized atoms.

Electrons: A negative charged particle that orbits the nucleus of an atom. It is lighter in weight than a proton or neutron.

Elements: An element is a substance made up of atoms with the same atomic number. 75% of the elements are metals and the others are nonmetals. A few examples are oxygen, iron, gold, chlorine, and uranium.

Fluorescence: Electrons absorb energetic radiation (for example ultraviolet light) raising an electron to a higher "Bohr" orbit. The energized electron soon drops down in a series of steps through lower energy states and in the process releases photons at lower energy states corresponding to visible light. The bright color occurs because the photons are concentrated in a narrow range of wavelengths.

Half-life: The period of time it takes for half the nuclei of a radioactive element to undergo decay to another nuclear form.

Isotope: An atom having the same number of protons in its nucleus as other varieties of the element but has a different number of neutrons.

Magnetic field: All magnetic fields are created by moving electric charge. The single moving electron around a nucleus is a tiny electric current. These orbiting electrons create magnetic fields and their net effect is to provide the atom with a magnetic field.

Neutron: A particle with no charge that is located in the nucleus of an atom.

Nuclear physics: A branch of physics that includes the study of the nuclei of atoms, their interactions with each other, and with constituent particles.

Nucleus: The central part of every atom that contains protons and neutrons.

Pitchblende: A brown to black fine grained, amorphous, variety of uraninite which has a dull luster and contains small quantities of uranium. Also called pitch ore or nasturan.

Phosphorescence: Luminescence that persists after a light source has been removed. Materials such as phosphors or phosphorogens are activated from a light source to emit the light in the form of photons of light.

Photosynthesis: The conversion of light to chemical energy. Using light energy, organic compounds are synthesized from carbon dioxide and water in the presence of chlorophyll.

Polonium: A chemical element, Po, atomic number 84. It is used in photographic film to reduce the static charge.

Proton: A positively charged particle that is located in the nucleus of an atom.

Radioactivity: A behavior of an element in which nuclei are undergoing change and emitting particles. This occurs naturally in approximately fifty elements. It can be produced artificially.

Radium: A chemical element, Ra, that has an atomic number 88. It is used as a source of neutrons and makes lightning rods more effective.

Thorium: A chemical element, Th, that has an atomic number 90. It is used in the manufacturing of sun lamps.

Transmutation: A nucleus process in which one nuclide is transformed into the nuclide of a different element.

Uranium: A chemical element, U, that has an atomic number 92. It reactive with nearly all nonmetals and is used as fuel for nuclear reactors.

X rays: Invisible electromagnetic radiation with wavelengths shorter than visible light. X rays are produced when high energy charged particles collide with other charged particles or with atoms.