Some large fraction of experimental work in nuclear physics concerns exploring the boundaries of what nuclei exist in nature and how they behave. Nature allows nuclei - made of protons and neutrons - in certain combinations only. Broadly speaking, the number of protons and neutrons should be similar, and not too large. The conditions are set by the fact that protons like sticking to neutrons and vice versa, but not so much to each other, but as long as there are roughly equal amounts then it's okay, and that protons, being electrically positively charged, don't like to congregate together in large numbers. This second effect means that when you start getting to the heavier elements (with >20 protons, say) then the proton to neutron ratio favours neutrons.
One of the most "exotic" nuclei with the same number of protons and neutrons yet observed in the laboratory is Tin-100, with 50 protons and 50 neutrons. This is a particularly special case, since 50 is a so-called magic number in nuclei, which means that having 50 particles of one type is a particularly stable configuration. The fact that it is heavy and does not have the excess of neutrons to balance the repulsive electric force means that it is nevertheless a bit on the unstable side.
Still, having these magic numbers makes it important to study, as the structure should be particularly clean and easy to understand from a theoretical point of view, which is why my colleagues have just published this article in Nature describing some of its properties. Particularly they have looked at the beta-decay, which gives a measure of the structure of the nucleus as a proton decays into a neutron to turn it in to the neighbouring nucleus Indium-100.
Good job Surrey colleagues, and I'm sure our REF coordinator will be pleased, too.
