Pop quiz: What shape is the nucleus of an atom? If you said spherical, you’re right - for almost every isotope of almost every element. But in some weird cases, it seems that the protons and neutrons arrange themselves into football-like shapes. Physicists have been studying these nuclear mutants since their existence was postulated for atoms with between 51 and 67 protons. In the late 1980s, Russian scientists used the idea to explain some baffling behavior of radioactive iodine and cesium.
Now physicists at Argonne National Laboratory in Illinois and colleagues elsewhere have determined that far heavier atoms - specifically isotopes of Europium (Eu) and Holmium (Ho), containing 63 and 67 protons respectively - also have “highly deformed” nuclei.
As reported in Physical Review Letters, the researchers measured the rate at which Eu and Ho engage in a rare form of radioactivity: proton emission. In most cases, radioactive stuff gives off alpha particles, electrons or gamma rays. But a few atoms kick out a proton, and the rate of that ejection depends on the shape of the nucleus. By measuring the atoms’ radioactivity rate, the team found evidence of the football form.