NARM	Any naturally occurring or accelerator produced radioactive materials. Does not include byproduct, source, or special nuclear material.
NATURAL RADIATION	Ionizing radiation arising from radioactive material other than the one directly under consideration. Natural radiation due to cosmic rays, soil, natural radiation in the human body. The levels of natural radiation vary with location, weather patterns etc. It is not from man-made sources.
NEUTRON	An uncharged elementary particle with a mass slightly greater than that of the proton and found in the nucleus of every atom heavier than hydrogen.
NON-REMOVABLE	Contamination adhering to the surface of structures, objects, areas or personnel that will not be removed or wiped up by physical or mechanical means during the course of a survey or during decontamination efforts.
NORM	Naturally occurring radioactive material.
NUCLEAR REGULATORY COMMISSION (NRC)	An independent federal regulatory agency responsible for licensing and inspecting nuclear power plants, universities and other facilities using radioactive materials. Licensees are required to comply with the NRC rules and regulations.
NUCLEUS	The small, central, positively charged region of an atom that carries essentially all the mass. Except for the nucleus of ordinary (light) hydrogen, which has a single proton, all atomic nuclei contain both protons and neutrons. The number of protons determines the total positive charge or atomic number (Z). The total number of neutrons and protons is called the mass number (A).
NUCLIDE	A species of atom characerized by its mass number, atomic number, and energy state of its nucleus, provided that the atom is capable of existing for a measurable time.