Radioactive Materials Section
General Definitions used in Health Physics & Radiation Protection

H

Half-life
The time in which one half of the atoms of a particular radioactive substance disintegrates into another nuclear form. Measured half-lives vary from millionths of a second to billions of years. Also called physical or radiological half-life.

Half-life, Biological
The time required for the body to eliminate one half of the material taken in by natural biological means.

Half-value, layer
The thickness of any given absorber that will reduce the intensity of a beam of radiation to one half of its initial value.

Health Physics
The science concerned with recognition, evaluation, and control of health hazards from ionizing radiation.

Health Physicist
A person who works in the area of environmental health engineering that deals with the protection of the individual and population groups against the harmful effects of ionizing and non-ionizing radiation. The health physicist is responsible for the safety aspects in the design of processes, equipment, and facilities utilizing radiation sources, so that radiation exposure to personnel will be minimized, and will at all times be within acceptable limits.

High radiation area
An area, accessible to individuals, in which radiation levels from sources external to the body could result in an individual receiving a dose equivalent in excess of 0.1 rem (1 mSv) in one hour at 30 centimeters from the radiation source or from any surface that the radiation penetrates.

Hospital
A facility that provides as its primary functions diagnostic services and intensive medical and nursing care in the treatment of acute stages of illness.

Human use
The internal or external administration of radiation or radioactive materials to human beings.

I

Individual
Any human being.

Individual monitoring means:

Individual monitoring devices or individual monitoring equipment
Devices designed to be worn by a single individual for the assessment of dose equivalent such as film badges, thermoluminescence dosimeters (TLDs), pocket ionization chambers, and personal ("lapel") air sampling devices.

Industrial radiography
The examination of materials by nondestructive methods utilizing sources of radiation.

Inhalation class
(see "Class" defined above).

Inspection
An official examination or observation to determine compliance with rules, orders, requirements and conditions of the agency or the Commission.

Internal dose
That portion of the dose equivalent received from radioactive material taken into the body.

Ion

Ionization
The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules, thereby creating ions. High temperatures, electrical discharges, or nuclear radiations can cause ionization.

Ionization Chamber
An instrument that detects and measures ionizing radiation by measuring the electrical current that flows when radiation ionizes gas in a chamber, making the gas a conductor of electricity.

Ionizing Radiation
Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions.  Some examples are alpha, beta, gamma, X-rays, neutrons. High doses of ionizing radiation may produce severe skin or tissue damage.

Isotope
One of two or more atoms with the same number of protons, but different numbers of neutrons in their nuclei. Thus, carbon-12, carbon-13, and carbon-14 are isotopes of the element carbon, the number denoting the approximate atomic weights. Isotopes have very nearly the same chemical properties, but often different physical properties (for example, carbon-12 and -13 are stable, carbon-14 is radioactive).

J

Joule
The SI unit of work and energy.  It represents the work done when a force on one (1) Newton is exerted through a distance of one (1) meter. 

K

K-capture
The radioactive transformation process by which one of the extra-nuclear electrons is captured by the nucleus, and unites with an intra-nuclear proton to form a neutron and emit a neutrino.

Kilo-
A prefix that multiplies a basic unit by 1,000.

L

Lethal Dose 50/30 (LD_50/30)
The dose of radiation expected to cause death within 30 days to 50% of those exposed.   Generally accepted to range from 400 to 600 rem (4-6 Gray)received over a short period of time.

Lens Dose Equivalent or "LDE"
applies to the external exposure of the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 cm (300 mg/cm²)

License
Except where otherwise specified, means a license issued pursuant to Section .0300 of the North Carolina Regulations for Protection Against Radiation.

Licensee
Any person who is licensed by the agency pursuant to Section .0300 of the North Carolina Regulations for Protection Against Radiation.

Licensing state
Any state designated as such by the Conference of Radiation Control Program Directors, Inc. Unless the context clearly indicates otherwise, use of the term Agreement State in this Chapter shall be deemed to include licensing state with respect to naturally occurring and accelerator produced radioactive material (NARM).

Limits or dose limits
The permissible upper bounds of radiation doses.

Linear Energy Transfer (LET)
The measure of the linear rate of energy absorption by the absorbing medium as the ionizing radiation traversed the medium.

Lost or missing licensed radioactive material
Licensed radioactive material whose location is unknown. It includes material that has been shipped but has not reached its destination and whose location cannot be readily traced in the transportation system.

Low-level radioactive waste
Means low-level radioactive waste as defined in North Carolina General Statute 104E-5(9a) and includes naturally occurring and accelerator produced radioactive material which is not subject to regulation by the U. S. Nuclear Regulatory Commission under the Atomic Energy Act of 1954, as amended, and is suitable for land disposal under the provisions of 15A NCAC 11 .1200 "Land Disposal of Radioactive Waste."

Lung class
(see "Class" as defined above).

M

Mega-
A prefix that multiplies a basic unit by 1,000,000.

Member of the public
Any individual except when that individual is receiving an occupational dose.

Micro-
A prefix that divides a basic unit into one million parts (i.e., 1/1,000,000).

Milli-
A prefix that divides a basic unit by 1,000 (i.e., 1/1000).

Minor
An individual less than 18 years of age.

Misadministration
Means the administration of the following:

Mobile nuclear medicine service
Means the transportation and medical use of radioactive material.

Molecule
A group of atoms held together by chemical forces. A molecule is the smallest unit of a compound that can exist by itself and retain all of its chemical properties.

Monitoring ("radiation monitoring" or "radiation protection monitoring")
The measurement of radiation levels, concentrations, surface area concentrations or quantities of radioactive material and the use of the results of these measurements to evaluate potential exposures and doses.

N

Nano-
A prefix that divides a basic unit by one billion (i.e., 1/1,000,000,000).

Natural radioactivity
Radioactivity of naturally occurring nuclides.

Neutrino
A electrically neutral particle of very small (probably zero) rest mass and of spin quantum number  �.  Postulated by Pauli in explaining the beta decay process.   Neutrinos and antineutrinos can penetrate amounts of matter measured in light years without appreciable attenuation.

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.

Noble Gas
A gaseous chemical element that does not readily enter into chemical combination with other elements. An inert gas.

NORM
An acronym for Naturally Occurring Radioactive Material

Nonstochastic effect
Health effects, the severity of which varies with the dose and for which a threshold is believed to exist. Radiation-induced cataract formation is an example of a nonstochastic effect (also called a deterministic effect).

NRC
United States Nuclear Regulatory Commission or its duly authorized representatives.

Nucleus; nuclei (plural)
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. This is the same for all the atomic nuclei of a given chemical element. The total number of neutrons and protons is called the mass number.

Nuclide
A general term referring to all known isotopes, both stable (279) and unstable (about 5,000), of the chemical elements.

O

Occupational dose
The dose received by an individual in the course of employment in which the individual's assigned duties involve exposure to radiation or radioactive material from licensed and unlicensed sources of radiation, whether in the possession of the licensee or registrant or other person. Occupational dose does not include dose received from background radiation, as a patient from medical practices, from exposure to individuals administered radioactive material and released in accordance with 15A NCAC 11 .0358 of this Chapter, from voluntary participation in medical research programs, or as a member of the general public.

P

Parent
A radionuclide that upon radioactive decay or disintegration yields a specific nuclide (the daughter).

Particle accelerator
Any machine capable of accelerating electrons, protons, deuterons, or other charged particles.

Periodic Table
An arrangement of chemical elements in order of increasing atomic number. Elements of similar properties are placed one under the other, yielding groups or families of elements. Within each group, there is a variation of chemical and physical properties, but in general, there is a similarity of chemical behavior within each group.

Person
Any individual, corporation, partnership, firm, association, trust, estate, public or private institution, group, agency, political subdivision of this state, any other state or political subdivision or agency thereof, and any legal successor, representative, agent or agency of these entities.

Periodic training
A periodic review conducted or provided by the licensee or registrant for its employees on radiation safety aspects of radiography. The review shall include the results of internal inspections, new procedures or equipment, accidents or errors that have been observed, and opportunities for employees to ask safety questions.

Permanent radiographic installation
An enclosed shielded room, cell, or vault in which radiography is performed.

Personnel monitoring equipment
Devices, such as film badges, pocket dosimeters, and thermoluminescent dosimeters, designed to be worn or carried by an individual for the purpose of estimating the dose received by the individual.

Pharmacist
An individual licensed by this state to compound and dispense drugs, prescriptions and poisons.

Physician
An individual currently licensed to practice medicine in this state.

Pico-
A prefix that divides a basic unit by one trillion (i.e., 1/1,000,000,000,000).

Planned special exposure
An infrequent exposure to radiation, separate from and in addition to the annual dose limits.

Positron
A particle with the same mass as an ordinary electron.  It has a positive electrical charge of exactly the same amount as an electron.  Positrons are created either by radioactive decay of certain unstable nuclei, or in collisions between photons of greater than 1 MeV and electrically charged particles or photons.  A positron does not decay, but rather will collide with an ordinary electron and in this collision, the positron-electron pair is annihilated.  This results in the coincident emission of two photons, each with an energy of 0.511 MeV.  These photons are are emitted 180� apart, making spatial localization possible.

Prescribed dosage
The quantity of radiopharmaceutical activity documented in a written directive by an authorized user.

Prescribed dose means:

Projection sheath
A flexible or rigid tube for guiding the source assembly and the attached control cable from the exposure device to the exposure head. When the source assembly is fully extended to the exposure head, the sealed source is in what is commonly called the working position.  Commonly called a guide tube or "J" tube.

Proton
An elementary nuclear particle with a positive electric charge and a mass slightly less than that of a neutron but about 1836 times greater than that of an electron,   located in the nucleus of an atom.

Public dose
The dose received by a member of the public from exposure to radiation or radioactive material released by a licensee or registrant, or to another source of radiation within a licensee's or registrant's control. It does not include occupational dose or doses received from background radiation, as a patient from medical practices, from exposure to individuals administered radioactive material and released in accordance with Rule .0358 of this Chapter, or from voluntary participation in medical research programs.

NCDENR .  Division of Radiation Protection .  1645 Mail Service Center, Raleigh, NC 27699-1645 . Voice: (919)-571-4141 .  Facsimile: (919) 571-4148 . Questions/Comments?