An international team at the ISOLDE facility showed that some atomic nuclei can assume asymmetric, "pear" shapes. The observations contradict some existing nuclear theories and will require others to be amended. Published in the journal Nature, a technique pioneered at ISOLDE was used successfully to study the shape of the short-lived isotopes Radon 220 and Radium 224.
Most nuclei have the shape of a rugby ball. While state-of-the-art theories are able to predict this behaviour, the same theories have predicted that for some particular combinations of protons and neutrons, nuclei can also assume asymmetric shapes, like a pear. In this case there is more mass at one end of the nucleus than the other.
In contradiction with some nuclear theories, Radium 224 is pear-shaped, Radon 220 does not assume the fixed shape of a pear but rather vibrates about this shape.
Such exotic atoms with pear-shaped nuclei could help with the searches for electric dipole moments (EDMs), that is the separation of positive and negative charges within the atom.