🚀 go-pugleaf

Currently I am preparing for my final Ph.d. examination in Tc-chemistry.
Therefore I should know, why only radioactive Tc-isotopes exist. But this
is indeed not a trivial question.

A short and simple explanation would be, that according to Mattauch's rule
no stable Tc-isotopes should exist. Mattauch's rule is a consequence of the
general beta-stability rules. Exceptions are mass numbers 50 and 180.

Mattauch's (empirical) rule says, that no neighbouring stable isobars
(nuclides of the same mass number) exist. So stable isobars have to differ
in two units. If you look at the "chart of nuclides" you can see, that all
Tc-isotopes nearby the "line of beta-stability" have stable isobars. For
example Tc-98 (the longest-lived Tc-isotope) has the stable neighbours Ru-98
and Mo-98. The isotopes Tc-90,91,93,103 and Tc-105 - Tc-110, which have no
stable neighbouring isobars are radioactive because they are to far away from
the "line of beta-stability".

But why are especially Tc and Pm the beta-unstable elements? What makes them
so unique? Until now, I did not find a satisfying explanation in literature.
Who has an idea about this or wants to discuss the question?

Hans-Juergen
Institute for chem.Technology
KFA-Juelich GmbH