Why is astatine so radioactive? I have heard and read about astatine's radioactivity, and it makes no sense to me. Why is it so unstable?  Uranium has a half life ranging from 70 to 4.5 billion years (natural isotopes), and it has 7 extra protons to deal with. I know that atomic nuclei can be stabler if they are spherical, implying that if you make a nucleus that isn't spherical you could destabilize it, but astatine has a maximum half life of 8 hours. Can someone explain this to me?

Information came from a few sources, including SciShow and Wikipedia.
I don't think there is an actual answer to that. What we know about the radioactivity is based mostly on empiric observation and quantum physics is still not able to give precise answers about the process of radioactive decay. 

A similar question could be asked about technetium: why is it unstable, even though it stands in the periodic table between stable elements? Probably it's a matter of their proton and neutron configuration that for some reason are particularly unstable compared to their neighbourhood, but there is still no equation capable of giving the half-life of an isotope.

This has already been discussed and probably we will have to wait until the atom nucleus is better studied before being able to answer this question.