How many neutrons can an atom hold?

Now, I think that I've mentioned that there is a theory that the interaction between the protons and the neutrons keeps the nuclei of atoms stable. Which is why most atoms occuring in nature do not deviate from the 1:1 ratio too much without being radioactive. The research in this area is still ongoing with lots of interesting news which really can be so ground breaking that it can change what we know/understand sometimes. Case in point:

A group of scientist, from Michigan State University, who were working on heavy aluminium and magnesium, found that the protons and neutrons do not have to be evenly numbered. With neutrons twice the number of protons, some heavy aluminium and magnesium were found with stability long enough for detection. (of course they decay shortly afterwards)

"They fired a beam of high-energy calcium ions into a sheet of tungsten, producing new elements. Among them, neutron-rich versions of aluminium and magnesium could be spotted in the few milliseconds before they decayed.

The researchers found an isotope of magnesium with 28 neutrons (magnesium-40) — more than twice its normal complement. That's bigger than the previous heaviest magnesium isotope found, which had 26 neutrons."

Read more about it in an article with the same title @ Nature (Published online 24 October 2007 | Nature | doi:10.1038/news.2007.189). Log-in using the NLB Digital library.