[Gallex] Germanium extraction and conversion

[Phys2]

Bonjour à tous,

J'étudie en ce moment le système de détection de neutrinos, le Gallex. Ce système a alors une partie de traitement chimique importante.

Néanmoins, même si je dispose d'un document qui donne les renseignements que je cherche, je ne connais pas très bien les termes techniques en anglais, et je n'ai pas grande connaissance de la chimie (je m'intéresse davantage à la physique).

Voici le texte en question (trouvé sur ce site) :

Citation:

At the beginning of a new run (i.e. start of exposure) a carrier solution containing about 1 mg stable Ge carrier is added to the GaCl3 solution. For this the non-radioactive isotopes 72Ge,74 Ge and 76Ge, later also 70Ge, are sequentially used in order to monitor carryover from one run to the next one. After three or four w eeks of exposure time, desorption starts by purging the target solution with 1900 m3 of nitrogen in 20 hours. Because tank A is equipped with a more efficient sparger system, the desorption time there is reduced to 12 hours. Germanium is removed from the solution as volatile germanium chloride (GeCl4 ). The gas stream is passed through a system of w ater scrubbers where the GeCl4 is absorbed. At the end of desorption all the germanium is contained in a volume of ab out 30 liters in the first scrubber. A series of smaller columns serves to further concentrate the germanium in a volume of ab out 1 liter of water. The final concen tration step is an extraction in to CCl4 and a back-extraction in to 50 ml of tritium-free water. This step also serves to separate the germanium from any tritium in the tank or the absorber system, since tritium would contribute to the bac kground in 71Ge counting. The last part of the chemical procedure is the conversion of GeCl4 to the gas GeH4 by means of the reducing reagent sodium borohydride (NaBH4). The GeH4 is dried and purified by gas chromatography . Its volume is then measured in order to determine the overall yield of the chemical procedures. Finally , it is placed together with xenon in to a miniaturized prop ortional coun ter. The volume ratio Xe:GeH4 is 70:30, the total counting gas pressure is about 800 Torr. The total chemical yield (i.e. the ratio Ge amount in the counter to the amount of Ge carrier added to the target solution at the beginning of the run) w as on the a v erage 85.6 % for the runs up to B34. Starting with B35, a slight modification of the absorber columns increased this average to 91.8 %. Due to the faster desorption in the A tank, total yields are now about 99 %.

J'aimerais alors avoir quelques explications sur la conversion du GeCl₄ en GeH₄, ainsi que sur le rôle du Xénon.

Quelqu'un pourrait-il m'aider ?

Merci d'avance
Phys2