DR MITSUO OHTSUKI/SCIENCE PHOTO LIBRARY Researchers have produced the lightest version of a uranium atom ever. It has only 122 neutrons compared with the 146 neutrons found in more than 99 per cent of the world’s naturally occurring uranium, which is known as uranium-238. Isotopes of an element always have the same number of protons – in uranium’s case, 92 – but differing numbers of neutrons. Isotopes are labelled by the total number of protons and neutrons that their nuclei contain, and the new isotope has the lowest number of those particles ever at 214, making it uranium-214. Advertisement Zhiyuan Zhang at the Chinese Academy of Sciences and his colleagues produced the new isotope through a time-consuming process involving blasting samples of tungsten with powerful beams of argon and calcium