Hi!

My educated guess would be the following:

Here on earth Xe 129, 131, 132 and 134 are the most common stable isotopes. These are also the heaviest stable ones.

On the other hand in the vicinity of the sun you have a lot of neutrons due to the fusion reaction in the sun. Through a quick google search I found that especially Xe129 has a very large cross section for neutron capture (http://www.google.at/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&ved=0CGwQFjAG&url=http%3A%2F%2Fwww.ubka.uni-karlsruhe.de%2Fcgi-bin%2Fpsview%3Fdocument%3Dfzk%2F6694&ei=RuwtUZCFAaeA4gTepIHICA&usg=AFQjCNEO9YkpmyfF6IRbfTH8_2mKQL0rZw&bvm=bv.42965579,d.bGE) which can make this atom unstable (it will then decay to something else) - I would check all the other cross sections for the stable Xe isotopes (if they are also larger for the heavier atoms then it is more likely that the lighter isotopes of Xe will survive near the sun which makes the average weight smaller there than here on earth).

Then you can countercheck for the cross sections of Kr80, Kr84 and Kr86 (you don't nesessary need Kr82 and Kr83 as neutron caption would produce another stable atom for those). Some of these cross sections are found here:

http://prc.aps.org/pdf/PRC/v35/i3/p936_1

if the cross section for neutron capturing are similar, the propability of producing unstable Kr isotopes which can decay in something else is equaly distributed. Hence the average Krypton mass will not be affected by the neutrons from the sun. Therefore the average mass will be approximately the same near the sun and here on earth (or on mars).

Maybe that helps, please let me know if there is something true in my assumptions (its a very interesting question).

good luck

Hannes

Dear Hannes, thank you for the prompt response. I would like to hope that your processes are real, though I am not sure that the solar noble gases can be disturbed by the solar neutrons (?). It is my fault that the presented initial information turned out to be insufficient. It is a matter of specific primordial (the so-called “planetary”) gases, which existed in the early solar system and were captured by some high-temperature solid phases found in some meteorites (in particular, in the Mars meteorites – shergotites). The noble gas isotopic systems could be changed during MHD-processes at the solar system formation, which give us a subtle instrument to study their peculiarities. Since you are a specialist in plasma physics and you are young, you have a chance, as well as a lot of time, to elaborate a new MHD-model of the solar system origin. All the questions are considered in detail in my article “On the Problem of Solar System Origin: The Regularities of Noble Gas Fractionation in Shock Waves”, published in English in the journal “Solar System Research” V. 41. N 3. 231-235. 2007, the reprint of which is attached. Good luck. Galina

Oh, then I misunderstood your question (and again learned something new) - thank you for the paper. :)