Stupid Questions January 2015

Gondolinian

This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.

Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.

To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.

Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.

To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.

Is anyone aware of the explanation behind why technetium is radioactive while molybdenum and ruthenium, the two elements astride it in the periodic table are perfectly normal? Searching on google on why certain elements are radioactive are giving results which are descriptive, as in X is radioactive, Y is radioactive, Z is what happens when radioactive decay occurs, etc. None seem to go into the theories which have been proposed to explain why something is radioactive.

The dynamics of the strong nuclear force are not well understood when high numbers of nucleons are involved. By which I mean, we have some empirical models that kinda-sorta work for various regimes, given some tinkering with the constants, but we have no from-first-principles understanding. You by no means need to go as far as biology before you get into stuff we cannot calculate from the equations; but in this case we don't even know the equations all that well, because the strong-force constant (ie, the equivalent of G in gravity and alpha in electromagn... (read more)

2Galap11y

Here's what I know about the matter: At low atomic number, isotopes that are more stable tend to be close to a 1:1 ratio of neutrons to protons. At high atomic number, this ratio approaches 3:2. I do not know why this is the case, and I believe it is not entirely understood by anyone. Also, this is not a very good predictor anyway. The real problem is that unlike electron energy levels in an atom, which are well known and easily approximable by various systems and techniques, the nuclear energy levels are not very well understood, and I think to an extent they are even difficult to measure. I believe it is known that unlike the electrons' spherical potential well, the nucleons are bound in a well that is a mixture of a spherical and cubic well, and the exact form is unknown, thus we can't predict the levels very well. I don't know why this is the case, and I believe it is not entirely understood by anyone else either. In short, I think that a good theoretical model that predicts these kind of things has yet to come.

1gwillen11y

Looking at http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCE/nuclearImages/islandOfStability.jpg , one of the patterns I see is that even numbers of protons and neutrons are systematically more stable than odd numbers. So that might answer the specific part of your question about its neighbors. (As to why even numbers, I don't know but I bet it's related to spins.) EDIT: Apparently this is enough of a thing that it even has its own Wikipedia page. http://en.wikipedia.org/wiki/Even_and_odd_atomic_nuclei