E

• Effective biological lifetime

  Arithmetic mean of the lifetime of a radioactive species in a living organism.

• Effective biological period

  Time interval needed for the amount of a radionuclide incorporated into a living organism to be reduced by half. Its calculation takes into account the fact that this material disappears through two simultaneous channels: radioactive decay and elimination via natural biological means (sweat, excretion, etc.).

• Effective dose (effective dose equivalent)

  The equivalent dose weighted (corrected proportionally to) by the varying sensitivity of the different organs and tissues of the human body. The correction factors are called tissue weighting factors. It is measured in sieverts (Sv): 1 Sv = 1 J/kg. The old unit was the rem: 1 Sv = 100 rem. Until quite recently, this term was known as "effective dose equivalent", but the latest recommendations from the ICRP have simplified the name.

• Elastic collision

  Encounter between elementary particles in which there is no loss of kinetic energy. It can be compared to the collision between two snooker balls.

• Electron

  Stable elementary particle that is part of the most external region (crust) of atoms and has the smallest known negative charge. This charge, which is taken in physics as a unit, equals 1.602 E-19 coulomb. Its rest mass is 1/1836.2 that of the proton.

• Electron capture

  Radioactive transformation in which the nucleus captures one of its core electrons.

• Electron-volt (eV)

  Kinetic energy acquired by an electron when it goes through an electric potential difference of one volt in a vacuum. It equals 1.602 E-19 joule.

• Encapsulated/non-encapsulated source

  An encapsulated source consists of radioactive substances firmly incorporated into solid and effectively inactive matter, or contained within an inactive enclosure that displays sufficient resistance to avoid any scattering of those radioactive substances, under normal conditions of use. When a source contains radioactive material in the absence of these restrictions, i.e., when the presentation and conditions of use do not enable any scattering of the radioactive substance it contains to be prevented, it is known as a non-encapsulated source.

• Enrichment

  Operation that involves increasing the isotopic abundance of a nuclide in a substance. In nuclear materials, enrichment refers to fissionable materials.

• Equivalent dose

  The absorbed dose weighted (corrected in proportion to) by the varying biological effectiveness of the different kinds of radiation on the live medium being considered. The correction factors are called "radiation weighting factors" (formerly radiation quality factors). It is measured in sieverts (Sv): 1 Sv = 1 J/kg. The old unit was the rem: 1 Sv = 100 rem.

• Exposure

  1. Physical magnitude that characterises the ionisation that a radiation causes in the air. It is measured in roentgen (R): 1 R = 2.58 E-4 coulomb/kilogramme. 2. Effect of subjecting or being subjected to ionising radiation.

• External cooling circuit

  Circuit employing water taken from a natural source (river, dam, lake, sea) and used to condense the water steam once it has moved the turbine, similarly to those used in any other coal, fuel oil or gas power station. The water from the external cooling circuit is returned in a controlled manner to the river, dam, lake or sea at a temperature slightly higher than that at which it was taken. This water does not come into direct contact with the nuclear fuel.