[mppm]

Close, but not quite. The general tendency for large nuclei to be less stable is correct, but for any given size, there is something of a optimum proton/neutron ratio that is most stable, and either adding or removing neutrons will reduce the half-life (minus various complications involving magic numbers etc.). At the very neutron-rich end, isotopes tend to spontaneously and rapidly emit the excess neutrons, and at the very neutron-poor end they will spontaneously shed protons to stabilize themselves. If you map these boundaries on the table of nuclides, you get the so-called neutron and proton driplines, respectively, which delineate the isotopes that, as GGP put it, can be reasonably agreed to exist. If you are interested in this stuff, [1] is a decent overview.

This paricular article is about mapping out isotopes close to the proton-drip-line in a heavy synthetic element, with the particular result that excited states can be more long-lived than the ground state of the isotope. This again is nothing particularly new. Generally excited states are short-lived, but there are many known examples of inversion, with the most extreme being a rare, naturally occurring, isotope of Tantalum: Ta-180m. The ground state Ta-180 has a half-life of 8 minutes, while the excited state is de facto stable, with a still unknown half-life in excess of 3*10^17 years [2].

1. https://en.wikipedia.org/wiki/Island_of_stability

2. https://en.wikipedia.org/wiki/Isotopes_of_tantalum#Tantalum-...