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A symbol for positron.

A symbol for electron.

An acronym for emergency core cooling system.

An acronym for effective dose equivalent.
Reference: 10CFR20.1003; 10CFR30.4; 10CFR70.4; 10CFR76.4; DOE-EH-413-9713; DOE Order 6430.1A.

effective dose
A measure of dose in which the type of radiation and the sensitivity of tissues and organs to that radiation is taken into account.

Related to effective dose equivalent.

effective dose equivalent
The sum of the dose equivalents to the organ or tissue (HT) and the weighting factors (WT) applicable to each of the body organs or tissues that are irradiated.

Symbol: HE.
Acronym: EDE.
Related to absorbed dose.
Related to collective dose.
Related to committed dose equivalent.
Related to committed effective dose equivalent.
Related to dose.
Related to dose equivalent.
Related to effective dose.
Related to integral absorbed dose.
Related to total effective dose equivalent.
Related to tissue weighting factor.

effective half-life
The time required for the concentration of a radionuclide in a biological system to be reduced by one half. An effective half-life includes all processes of elimination, including radioactive decay.

Related to biological half-life.
Related to half-life.

effective multiplication factor
The measure of criticality in a given system. Effective multiplication factor is an indication of whether the number of neutrons produced by a fissionable mass is increasing or decreasing. When the effective multiplication factor is less than 1.0, the system is sub-critical; when the effective multiplication factor exceeds 1.0, the system is super-critical; and when the effective multiplication factor is exactly 1.0, the system is critical.

Symbol: Keff.
Synonym: criticality factor.
Related to cent.
Related to dollar.
Related to inhour.
Related to reactivity.

The probability an incident radiation will interact with a detection medium forming a recordable event. Efficiency can also be defined as the probability an incident radiation will deposit all its energy inside the detection medium. This definition is especially appropriate for gamma-ray spectroscopy where Compton scattering and other photon-interaction processes result in a degraded electrical signal and thus a loss of detected energy.

An acronym for emergency feedwater.

A chemical element with atomic number 99. Einsteinium Albert Ghiorso, Glenn Seaborg, and colleagues discovered Einsteinium by studying debris from a 1952 thermonuclear explosion that occurred in the South Pacific. The name einsteinium was given in honor of Albert Einstein.

Symbol: Es.

A radiation, particle or ion produced as the result of a nuclear reaction. It is used in the context of a nuclear reaction where the projectile interacts with a target nucleus, producing a product nucleus and an ejectile.

Related to product nuclide.
Related to projectile.
Related to target nuclide.

electromagnetic radiation
Radiation consisting of interacting electric and magnetic waves. Examples include gamma rays, x-rays, ultraviolet and visible light.

Acronym: EMR.
Synonym: photon.
Related to gamma ray.
Related to ionizing radiation.
Related to nonionizing radiation.
Related to x-ray.

A basic constituent of the atom. The electron is a fundamental particle that has a mass of 0.000548579903 ± 0.000000000013 atomic mass units (0.51099907 ± 0.00000015 MeV). A free, unbound electron is stable against radioactive decay. The electron is a lepton with a spin of 1/2 and a charge of -1. The positron is the antiparticle of the electron.

Symbol: e-.
Synonym: corpuscle.
Synonym: negative thermion.
Synonym: negaton.
Synonym: negatron.
Related to positron.

electron binding energy
A synonym for ionization potential.

electron capture
A synonym for electron capture decay.

electron capture decay
Radioactive disintegration by capture of an atomic electron. Electron capture belongs to the general category of beta decay.

Symbol: e-c.
Synonym: electron capture.
Related to alpha decay. Related to beta decay. Related to spontaneous fission.

electron volt
A unit of energy defined as 1.60919x10-19 joules. It is the energy required to raise an electron through a potential difference of 1 volt. The electron volt is not an SI unit but its use is valid unit within the International System of units.

Symbol:  eV.
Symbol: (obsolete) ev.
Related to joule.

(1) One or more nuclides, or a population of such nuclides with a specific number of protons. A chemical element.
(2) The chemical elements uranium or plutonium.

element X
(obsolete term)

A synonym for holmium.

elemental abundance
The relative concentration of a particular element (in any chemical form) as found in nature. This term should not be confused with isotopic abundance.

Related to cosmic abundance.
Related to isotopic abundance.

A symbol for emanation.

(obsolete term)

Symbol: Em.
A synonym for radon.

(obsolete term)

A synonym for radon.

emergency core cooling system
A backup coolant system for reactors that automatically activates when the primary coolant system fails. It is designed to limit the temperature of the reactor core and thereby prevent damage. Upon activation of the backup coolant system, the reactor scrams, reducing the heat output of the core. Latent heat produced from the decay of fission products in the core requires continued cooling after the reactor has been scrammed.

Acronym: ECCS.

emergency feedwater
Acronym: EFW.
A synonym for auxiliary feedwater.

An acronym for electromagnetic radiation.

The capacity for doing work.

energy level diagram
A synonym for level scheme.

enriched uranium
Uranium in which the nuclide 235U has an isotopic abundance of greater than is found in nature. It is greater than approximately 0.711%.

Related to depleted uranium.
Related to natural uranium.

Synonym for isotopic enrichment.

Environmental Protection Agency
[From the Environmental Protection Agency Web Site.]

The mission of the U.S. Environmental Protection Agency is to protect human health and to safeguard the natural environment--air, water, and land--upon which life depends.

EPA's purpose is to ensure that:
  • All Americans are protected from significant risks to human health and the environment where they live, learn and work.
  • National efforts to reduce environmental risk are based on the best available scientific information.
  • Federal laws protecting human health and the environment are enforced fairly and effectively.
  • Environmental protection is an integral consideration in U.S. policies concerning natural resources, human health, economic growth, energy, transportation, agriculture, industry, and international trade, and these factors are similarly considered in establishing environmental policy.
  • All parts of society--communities, individuals, business, state and local governments, tribal governments--have access to accurate information sufficient to effectively participate in managing human health and environmental risks.
  • Environmental protection contributes to making our communities and ecosystems diverse, sustainable and economically productive.
  • The United States plays a leadership role in working with other nations to protect the global environment.
Acronym: EPA.
Web Site: EPA

Synonym for Environmental Protection Agency.

epithermal neutron
A neutron with an energy greater than 0.025 eV and less than or equal to 1 eV.

Related to cold neutron.
Related to continuum region neutron.
Related to fast neutron.
Related to low energy region neutron.
Related to resonance region neutron.
Related to slow neutron.
Related to thermal neutron.
Related to ultra cold neutron.
Related to very cold neutron.

Any state where the creation or addition of a component equals the consumption or removal of that component. The term is often used in nuclear science in the context of the activity of a radioactive nuclide that is fed by a radioactive parent. The system is said to be in equilibrium when the rate of decay of the parent equals the rate of decay of the daughter.

Related to radioactive equilibrium.

equivalent dose
The absorbed dose expressed in terms of the potential injury that it could cause. It is the product of the absorbed dose, the quality factor, and all other necessary modifying factors at the location of interest. The SI standard uni for dose equivalent is the sievert.

Symbol: HT.
Synonym: ambient dose equivalent.
Synonym: directional dose equivalent.
Synonym: dose.
Synonym: dose equivalent.
Synonym: personal dose equivalent.
Related to absorbed dose.
Related to collective dose.
Related to committed dose equivalent.
Related to committed effective dose equivalent.
Related to dose.
Related to effective dose equivalent.
Related to integral absorbed dose.
Related to quality factor.
Related to total effective dose equivalent.
Reference: NUREG-0544, Rev. 4.

A symbol for erbium.

A chemical element with atomic number 68. Erbium was discovered in 1843 by Carl Gustaf Mosander. The name erbium is derived from Ytterby, a town in Sweden, the place of discovery.

Symbol: Er.
Related to lanthanides.
Related to rare earths.
Related to yttrium earths.

A unit of energy defined as exactly 1x10-7 J.

Related to joule.

A symbol for einsteinium.

A symbol for europium.

A chemical element with atomic number 63. Europium was discovered in 1890 by Paul-émile Lecoq de Boisbaudran who was conducting experiments on compounds of samarium and gadolinium. In his experiments, de Boisbaudran noticed spectral lines which he suggested were due to a new element that he was never able to isolate. In 1901 Eugène-Anatole Demarçay was credited for the discovery of europium because he was able to successfully isolate it. The name europium is derived from Europe.

Symbol: Eu.
Related to lanthanides.
Related to rare earths.
Related to terbium earths.

(obsolete term)
A symbol for electron volt. The accepted symbol is eV.

The symbol for electron volt.

exclusion area
(1) The area surrounding a reactor in which the reactor operator (licensee) has the authority to determine all activities. This includes limiting or excluding access to the area by personnel or property.

(2) A security area for the protection of classified matter where mere access to the area would result in access to classified matter.

A rapid increase in reactor power. Excursions may be accidental or they may be deliberate. A safety system test is an example of a deliberate excursion.

exotic atom
An atom whose nucleus is made of a positively-charged fundamental particle or in which an electron has been replaced by a negatively-charged fundamental particle.

Related to atom.
Related to inverted atom.
Related to positronium.
Related to mu-mesic atom.

Of or pertaining to the process of being exposed to ionizing radiation or to radioactive material.

Reference: 10CFR20.
Related to ionizing radiation.
Related to nonionizing radiation.

external dose
That portion of the dose equivalent received from radiation sources outside the body.

external radiation
Generally it is radiation from sources outside a body.

A hand, forearm, elbow, foot, ankle, lower leg, or knee. Extremities are often considered separately from the rest of the body because they are less susceptible to radiation.

Reference: 10CFR20.
eye dose equivalent
The external exposure of the lens of the eye. It is taken as the dose equivalent at a tissue depth of 0.3 centimeters (300 mg/cm2).

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