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Glossary
alpha particle
A positively charged particle made up of two neutrons and two protons emitted by certain radioactive nuclei. Alpha particles can be stopped by thin layers of light materials, such as a sheet of paper, and pose no direct or external radiation threat. However, they can pose a serious health threat if ingested or inhaled. [For additional information see Understanding Radiation: Alpha Particles.]
ambient air
The portion of the atmosphere external to buildings; the outside environment. The air that surrounds us.
background (radiation)
Natural radiation caused by sun exposure, cosmic rays from space, and radioactive elements found in the earth's crust. Radon, which emanates from the ground, is an example of natural radiation. Cosmic rays include energetic protons, electrons, gamma rays, and x-rays. The primary radioactive elements found in the earth's crust are uranium, thorium, and potassium, and their radioactive derivatives.
baseline
The concentration of a nuclide or radiation level that is considered "normal" under routine conditions. Baseline is generally obtained from evaluation (typically an average) of numerous background measurements. Baseline results are used for comparisons to individual sample results to determine if abnormalities may exist.
beta particles
An electron or positron emitted by certain radioactive nuclei. Beta particles can be stopped by aluminum. They can pose a serious direct or external radiation threat and can be lethal depending on the amount received. They also pose a serious internal radiation threat if inhaled or ingested. [For additional information see Understanding Radiation: Beta Particles.]
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curie (Ci)
A unit quantity of any radioactive nuclide in which there are 37 billion atomic transformations (disintegrations) in one second. A measure of radioactivity based on the observed decay rate of approximately one gram of radium. The Curie was named in honor of Pierre and Marie Curie, pioneers in the study of radiation. [For additional information see Understanding Radiation: Curies.]
| Units | |||||
|---|---|---|---|---|---|
| Factor | Prefix | Symbols | Factor | Prefix | Symbols |
| 1018 | exa | E | 10-1 | deci | d |
| 1015 | peta | P | 10-2 | centi | c |
| 1012 | tera | T | 10-3 | milli | m |
| 109 | giga | G | 10-6 | micro | µ |
| 106 | mega | M | 10-9 | nano | n |
| 103 | kilo | k | 10-12 | pico | p |
| 102 | hecto | h | 10-15 | femto | f |
| 101 | deka | da | 10-18 | atto | a |
dose
Denotes the quantity of radiation or energy absorbed. Dose may refer to the following:
--absorbed dose, the amount of energy deposited per unit mass;
--equivalent dose, the absorbed dose adjusted for the relative biological effect of the type of radiation being measured; and
--committed dose, a dose that accounts for continuing exposures over long periods of time (such as 30, 50, or 70 years).
[For additional information see Health Effects or Radiation Protection Basics.]
exposure
A term relating to the amount of ionizing radiation that strikes a living or inanimate material. (This is a general definition. In health physics, exposure is specifically defined as a measure of ionization in air caused by x-ray or gamma radiation only.) [For additional information see Understanding Radiation: Exposure Pathways.]
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fission
The splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation.
gamma rays
High-energy electromagnetic radiation emitted by certain radionuclides when their nuclei transition from a higher to a lower energy state. These rays have high energy and a short wavelength. All gamma rays emitted from a given isotope have the same energy, a characteristic that enables scientists to identify which gamma emitters are present in a sample. Gamma rays are very similar to x-rays. [For additional information see Understanding Radiation: Gamma Rays.]
ionizing radiation
Emissions from naturally occurring and man-made radionuclides, including alpha, beta, and gamma emissions.
isotope
A nuclide of an element having the same number of protons but a different number of neutrons. [For additional information see Nuclides and Isotopes.]
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monitoring
The use of sampling and detection equipment to determine the levels of radiation or other toxic materials in land, air, or water.
neutron
A small particle possessing no electrical charge and typically found within an atom's nucleus. A neutron has about the same mass as a proton. [For additional information see Understanding Radiation: What is an Atom?.]
nuclear energy
The heat energy produced by the process of nuclear reaction (fission or fusion) within a nuclear reactor or by radioactive decay.
nuclear fallout
Emission into the environment of radionuclides produced during a nuclear fission event.
nuclear fission
A type of nuclear reaction in which the nucleus of an atom splits into two nearly equal parts, rather than ejecting one or a few small nuclear particles, as in most nuclear reactions.
nuclear radiation
Particles (alpha, beta, neutrons) or photons (gamma) emitted from the nucleus of unstable radioactive atoms as a result of radioactive decay.
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particulates
Minute separate particles of material, typically airborne.
pathways
The ways in which people are exposed to radiation or other contaminants. The three basic pathways are inhalation (contaminants are taken into the lungs), ingestion (contaminants are swallowed), and direct (external) exposure (contaminants cause damage from outside the body).
picocurie (pCi)
One one-trillionth (1/1,000,000,000,000) of a curie.
proportional counter
A gas filled radiation detector that produces a signal which is proportional to the energy deposited by the ionizing radiation (alpha, beta, or gamma) that passes through or into it. Low background versions of these detectors are heavily shielded to exclude natural background radiation and so enhance detection sensitivity.
proton
A small particle, typically found within an atom's nucleus, that possesses a positive electrical charge. The number of protons is unique for each chemical element.
quality assurance (QA)
An integrated system of management activities involving planning, implementation, assessment, reporting, and quality improvement to ensure that a process, item, or service is of the type and quality needed and expected by the client.
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radioactive decay
The spontaneous disintegration of the nucleus of an atom with the emission of (alpha, beta, gamma, or x-ray) radiation.
radionuclides
"Versions" of chemical elements that are not stable, or in other words, are susceptible to undergoing radioactive decay.
risk
The probability of injury, disease, or death under specific circumstances. Risk can be expressed as a value that ranges from zero (no injury or harm will occur) to one hundred percent (harm or injury will definitely occur). Risk-based standards limit the risk that releasing a contaminant to the environment may pose rather than limiting the quantity that may be released.
absolute risk is the excess risk attributed to irradiation and usually expressed as the numeric difference between irradiated and non-irradiated populations (e.g., 1 case of cancer per million people irradiated annually for each rad). Absolute risk may be given on an annual basis or lifetime basis.relative risk is the ratio between the number of cancer cases in the irradiated population to the number of cases expected in the unexposed population. A relative risk of 1.1 indicates a 10 percent increase in cancer due to radiation, compared to the "normal" incidence.
station or site
Any installation, facility, or discrete, physically separate parcel of land, or any building or structure or portion thereof, that is being considered for survey and investigation.
x-rays
High-energy electromagnetic radiation emitted by atoms when electrons fall from a higher energy shell to a lower energy shell. These rays have high energy and a short wave length. X-rays are very similar to gamma rays.
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