The heaviest version of oxygen ever created falls apart mysteriously quickly. This finding implies a problem with our understanding of a fundamental force of nature.
Yosuke Kondo at the Tokyo Institute of Technology in Japan and his colleagues created oxygen-28 – an isotope of oxygen with eight protons and 20 neutrons – by smashing an energetic beam of fluorine atoms into liquid hydrogen.
The fluorine atoms each had 20 neutrons and nine protons. When they collided with the liquid hydrogen, they each lost a proton, turning the atoms into oxygen-28. The researchers expected these atoms to be stable. But instead, they found that they only existed for about a zeptosecond, or trillionth of a billionth of a second, and then decayed into the less heavy oxygen-24 and four neutrons.
“This is extremely surprising. It opens a very, very big fundamental question about nature’s strongest interaction, the nuclear strong force,” says Rituparna Kanungo at Saint Mary’s University in Canada, who was not involved with the experiment. The strong force binds quarks together to make protons and neutrons, but our understanding of how exactly it works when all those particles show up in large numbers is currently incomplete, she says.
Kondo and his team expected that oxygen-28 would hang around a lot longer because it was thought to be “doubly magic”.
Within the nucleus of every atom, protons and neutrons are grouped into shells, each of which can accommodate specific numbers of particles. When all occupied shells are fully filled, the number of particles within them is called “magic” and the nucleus that they comprise becomes extremely stable.
If both protons and neutrons fully fill an atom’s shells, then it is called doubly magic. The oxygen that sustains life on Earth has this property, which is what allows it to be so abundant.
Through various studies of isotopes like calcium-40 and nickel-48, seven numbers are widely recognised as being magic, including the number 20 for neutrons. The new experiment challenges this idea.
Theoretical models will have to be re-made, and more experiments will need to be done in order to get a sense of what the particles inside oxygen-28 actually do if they are not in full and stable shells, says Kanungo.