Lightest known form of uranium created
“Because neutrons have mass, uranium-214 is much lighter than common isotopes”
Scientists have discovered a new type of uranium – the lightest ever known. The discovery could reveal more about a weird alpha particle that gets ejected from certain radioactive elements as they decay. The newfound uranium, called uranium-214, is an isotope – a variant of the element – with 30 more neutrons than protons, one fewer neutron than the next lightest known uranium isotope. Because neutrons have mass, uranium-214 is much lighter than more common uranium isotopes, including uranium-235, which is used in nuclear reactors and has 21 extra neutrons. This newfound isotope isn’t just lighter than others, it also showed unique behaviours during its decay. As such, the new findings will help scientists better understand a radioactive decay process known as alpha decay, in which an atomic nucleus loses two protons and two neutrons, collectively called an alpha particle. Though scientists know that alpha decay results in the ejection of this alpha particle, after a century of study they still don’t know the exact details of how the alpha particle is formed before it gets ejected. The researchers created the new uranium isotope at the Heavy Ion Research Facility in Lanzhou, China. They shone a beam of argon at a target made of tungsten inside a machine called a gas-filled recoil separator, in this case the Spectrometer for Heavy Atoms and Nuclear Structure, or SHANS. By shining a laser at the tungsten, the researchers effectively added protons and neutrons to the material to create uranium. The new uranium-214 isotope had a half-life of just half a millisecond, meaning that’s the amount of time it takes for half of the radioactive sample to decay. The most common isotope of uranium, called uranium-238, has a half-life of about 4.5 billion years, which is about the age of Earth. By carefully watching how the isotopes decayed, the scientists were able to study the strong nuclear force, one of the four fundamental forces that hold matter together, acting on the alpha particle parts – the neutrons and protons – on the surface of the uranium. They found that the proton and neutron in each alpha particle interacted much more strongly than in isotopes and other elements with a similar number of protons and neutrons that have been previously studied. This is likely due to the specific number of neutrons inside the nucleus of uranium-214, the researchers said. The new isotope has 122 neutrons, nearing the ‘magic neutron
number’ of 126, which is especially stable due to the configuration of the neutrons in complete sets, or shells. With this configuration, it’s easier for scientists to calculate the strong force interaction between the protons and neutrons. That makes these isotopes particularly interesting to scientists, since studying these interactions can reveal features related to nuclear structure and decay processes, said Zhiyuan Zhang, a physicist at the Chinese Academy of Sciences. Scientists suspect this proton-neutron interaction could be even stronger in heavier radioactive elements such as isotopes of plutonium and neptunium. These elements have a few more protons, and the configuration of their orbits suggests they could have even stronger interactions than the uranium isotopes.