AW: request for help with Wikipedia article

[Franz Schönhofer <franz.schoenhofer@CHELLO.AT>]

Franz Schoenhofer

PhD, MR iR

Habicherg. 31/7

A-1160 Vienna

AUSTRIA

phone -43-0699-1168-1319







A few comments on Nathans questions and Mikes answers:





>Is it safe to assume that Cs137 is the majority of the remaining

activity?



I think so, yes. If I am wrong, I am sure someone on this list will

correct me.



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If you look at the curves showing the fission yield vs. fission products

mass numbers you see two peaks at around the mass numbers 90 and 137.

Therefore the most abundant radionuclides after fission are such ones

like Sr-90, I-131, I-132, Te-132, Cs-134, Cs-137 etc. Most of these,

including I-131, have short half-lifes, so they have decayed since long.

Sr-90 and Cs-137 are generated in approximately equal amount both mass

and activity, and they have a similar half-life. But during the

accident, the heat caused the Cs-isotopes to volatilize and they were

attached to aerosols and particles and distributed widely. Sr-90 is not

so easily volatilized, so most of it was deposited together with fuel

particles during the explosion in the vicinity of the damaged reactor or

left in the ruin with the debris. 



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>I assume some C14 was generated in the moderator, and a great deal of

that 

>made it into the atmosphere, but is that not a significant source of 

>contamination?



You ask good questions. What you say is reasonable, and I don't know the



answer.



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There is extremely little C-14 generated in a nuclear reactor, mostly by

"strange" fission events and not by an n,gamma activation reaction,

because graphite consists of almost entirely C-12. Naturally occurring

C-14 is generated at high altitudes by a nuclear reaction involving

nitrogen and the neutrons of the cosmic rays. This also happened at low

altitude with the nuclear bombs as neutron sources. Tritium is generated

in considerable quantities only in heavy water reactors like the

Canadian CANDU by activation of deuterium with neutrons. There were no

elevated C-14 or T activity concentrations observed in precipitation in

Europe. 

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--





I read the Wikipedia article, for which I have some comments - but I

will write them later. As a reliable source of numbers and facts I would

highly recommend IAEA sources.









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