An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The → process by which the relative → abundance of a given → chemical element or → species in an → astrophysical object is increased. For example the the → increase of the → heavy element content of the → interstellar medium due to → stellar evolution.

→ chemical; → enrichment.

The → enrichment of deuterium (D) with respect to → hydrogen (H) in → Solar System molecules when compared with the D/H ratio in the → interstellar → solar nebula. H-bearing molecules in → comets, → planets, and → chondrite  → meteorites show a systematic D enrichment relative to the → molecular hydrogen of the solar nebula. Because there is no nuclear source for D in the Universe, the observed → isotopic enrichment must have its origin in chemical reactions having faster reaction rates for D than for H. In the Solar nebula the → isotopic fractionation of D between → water and H followed the reversible reaction:
H₂O + HD ⇔ HDO + H₂.
At low temperatures, this reaction favors the concentration of D in HDO. In the → interstellar medium grain chemistry plays a crucial role in D enrichment. See also → enrichment factor.
Apart from → deuterium fractionation, D could be enriched through another mechanism. Since molecular hydrogen (H₂) is more → volatile than molecular deuterium (D₂), D/H ratio could increase in certain planets that orbit near their star.

→ deuterium; → enrichment.

The ratio between the D/H value in → water and in → molecular hydrogen, as expressed by:
f = [(1/2)HDO/H₂O]/[(1/2)HD/H₂] = (D/H)_H2O/(D/H)_H2.
When f> 1, there is → deuterium enrichment.

→ deuterium; → enrichment; → factor.

1) A process that changes the → isotopic ratio in a material. For example, for uranium the ratio of U-235 to U-238 may be increased by gaseous diffusion of uranium hexafluoride.
2) → chemical enrichment.

Verbal noun of → enrich.

The process by which the percentage of → fissile uranium in a sample is increased. Uranium obtained from mining contains several → isotopes of uranium in different compositions, such as U-238 (~99%), U-235 (~0.7%), and U-234 (~0.02%). Among them, U-235 is the only one that is fissile, i.e. can be used in a → nuclear reactor to produce heat (and consequently electricity) in a controlled manner. As such, the concentration of U-235 as a fuel used in a reactor needs to be increased, which is done using several techniques, such as → gaseous diffusion.

→ uranium; → enrichment.