NOTCH SENSITIVITY: A measure of the reduction in strength of a metal caused by the presence of stress
concentration. Values can be obtained from static, impact or fatigue tests.
NOZZLE: The outlet end of a gooseneck, or the fitting that joins the gooseneck to the sprue hole of the die.
NUCLEAR REACTION: A reaction involving an atoms nucleus, such as fission, neutron capture, radioactive decay,
or fusion, as distinct from a chemical reaction, which is limited to changes in the electron structure surrounding the
NUCLEAR REACTOR: A device by means of which a fission chain reaction can be initiated, maintained, and
controlled. Its essential component is a core with fissionable fuel. It usually has a moderator, a reflector, shielding,
and control mechanisms.
NUCLEAR TRANSITION (RT): A change in the energy state or level of an atomic nucleus which may, or may not,
result in the emission of radiation.
NUCLEUS: The heavy central part of an atom in which most of the mass and the total positive electric charge is
concentrated. With the exception of the nucleus of hydrogen, nuclei are composed of protons and neutrons. The
charge of the nucleus, an integral multiple of the charge of the electron, is the essential factor that distinguishes one
element from another chemically.
NUCLIDE: Any species of atom that exists for a measurable length of time. A nuclide can be distinguished by its
atomic weight, atomic number, and energy state. The term is used synonymously with isotope. A radionuclide is a
NUCLIDE (RT): A species of atom characterized by its mass number, atomic number, and nuclear energy state, and
that has a measurable mean life.
OBJECT-TO-FILM DISTANCE (RT): The distance from the tube or source side of the irradiated specimen to the film
surface, i.e., inclusive of specimen thickness. Abbreviation: ofd.
OCCUPANCY FACTOR (RT): The factor by which the workload should be multiplied to correct for the degree or type
of occupancy of the area in question. Symbol: T.
OCCUPATIONAL DOSE: The dose received by an individual in a restricted area or in the course of employment in
which the individual's assigned duties involve exposure to radiation. Occupational dose does not include dose received
from background radiation, as a patient from medical practices, from voluntary participation in medical research
programs, or a member of the general public.
OERSTED (MT): A unit of field strength that produces magnetic induction designated by the letter H. The Oersted is
numerically equal in air or in a vacuum. Oersted (H) refers to the magnetizing force tending to magnetize an
unmagnetized body, and Gauss refers to the field (B) so induced in the body.
OHM: The ohm is the unit of electrical resistance. It is the value of a resistance that will pass one ampere of current at
a potential of one volt.
OIL-COOLED TUBE (RT): An X-ray tube in which the heat produced is dissipated, directly or indirectly, by means of
OIL-IMMERSED TUBE (RT): An X-ray tube designed for operation in oil.