PARTICLE ACCELERATOR	Any machine capable of accelerating electrons, protons, deuterons, or other charged particles in a vacuum and of discharging the resultant particulate or other radiation into a medium at energies usually in excess of 1 MeV.
PERSONNEL MONITORING	The determination of the degree of radioactive contamination on individuals using surevy meters or the determination of radiation dosage received by means of dosimetry devices.
PHOTON	A quantum or packet of energy emitted in the form of electromagnetic radiation. Gamma rays and x-rays are examples of photons.
PIG	A container, usually lead, used to ship or store radioactive materials. The thick walls protect an individual handling the container from radiation. Large containers are commonly called casks.
POCKET DOSIMETER	A small ionization detection instrument that indicates radiation exposure directly. An auxiliary charging device is usually necessary.
POSITRON	A particle equal in mass, but opposite in charge, to the electron; a positive charge.
PRINCIPAL INVESTIGATOR	A faculty member, assistant professor or higher, appointed by the licensee, who has been approved through the Radiation Safety & Radioisotope Committee for the purchase and use of radioactive materials.
PROTECTIVE BARRIERS	Barriers of radiation absorbing material, such as lead, concrete, plaster and plastic, that are used to reduce radiation exposure.
PROTON	An elementary nuclear particle with a positive electric charge located in the nucleus of an atom.