Fr.: diaphragme d'ouverture
The diaphragm that limits the diameter of the axial light bundle allowed to pass through a lens.
Fr.: lumière catoptrique
Light that is reflected from a curved surface mirror.
Fr.: système catoprtique
An optical system in which the light is reflected only.
The area of → optics which treats of the laws and properties of light reflected from reflective surfaces.
Fr.: isotope fertile
An → isotope not itself → fissile but that is converted into a fissile isotope, either directly or after a short → decay process following absorption of a → neutron. Example: U-238 can capture a neutron to give U-239. U-239 then decays to Np-239 which in turn decays to fissile Pu-239. The most important fertile isotope is U-238. This is by far the most abundant isotope of natural uranium, making up 99.28%. The important transformation chain is: 92U238 + 0n1→ 93Np239 + β- (23.5 minutes) → 94Pu239 + β- (2.36 days).
Fr.: diaphragme de champ
A diaphragm located at an image plane of an optical system that determines the size and shape of the image. → aperture stop.
Fr.: isotope fissile
An isotope that is capable of undergoing nuclear fission after capturing either fast neutron or thermal neutron. Typical fissionable isotopes: 238U, 240Pu, but also 235U, 233U, 239Pu, 241Pu
izotop (#), hamjâ (#)
One of two or more atoms having the same number of protons in its nucleus, but a different number of neutrons and, therefore, a different mass.
Isotope, from → iso- + -tope, from Gk. topos "place."
Izotop, loan from Fr., as above. hamjâ, from ham- "together" → com- + jâ "place" (from Mid.Pers. giyag "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night").
Fr.: fractionnement isotopique
A slight difference between the → abundances of → isotopes of the same → chemical element owing to → physical or → chemical → processes. It results in the → enrichment or → depletion of an isotope. Same as → isotopic fractionation.
Fr.: décalage isotopique
A displacement in the spectral lines due to the different isotopes of an element.
Of or relating to an → isotope.
Fr.: fractionnement isotopique
Same as → isotope fractionation.
Fr.: nombre isotopique
The difference between the number of neutrons in an isotope and the number of protons. Neutron excess.
Fr.: rapport isotopique
The relative abundances of two isotopes of a given chemical element, such as D/H (deuterium/hydrogen), (carbon) 12C/13C, and (uranium) 235U/238U.
spin-e izotopi (#), izospin (#)
Fr.: spin isotopique
Same as → isospin.
Any of molecular entities which differ in their isotopic composition but retain the same → chemical elements, e.g. H2O and HDO.
Any of → isomers having the same number of each isotopic atom but differing in their positions. For example, CH3CHDCH3 and CH3CH2CH2D are a pair of isotopomers.
Short for isotopic isomers.
The boundary layer between a planet's → magnetosphere and the → magnetic field of the → solar wind. It borders the → magnetosheath and is defined by the surface on which the pressure of the solar wind is balanced by that of the planet's magnetic field. The front point of the Earth's magnetopause, on the sun-ward side of the Earth, is about 10 terrestrial radii, on average. This point can be closer or farther, because the magnetopause contracts or expands depending on the intensity of the solar wind.
From → magneto- + pause "break, cessation, stop," from M.Fr. pause, from L. pausa "a halt, stop, cessation," from Gk. pausis "stopping, ceasing," from pauein "to stop, to cause to cease."
From meqnât-→ magnet + marz "frontier, border, boundary," from Mid.Pers. marz "boundary;" Av. marəza- "border, district," marəz- "to rub, wipe;" Mod.Pers. parmâs "contact, touching" (→ contact), mâl-, mâlidan "to rub;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); Ger. Mark; E. mark, margin.
Of or relating to a → protoplanet or protoplanets.