Whereas that means 54calcium is slightly more stable than isotopes with one more or less neutron, the nucleus is still radioactive and tends to decay in a matter of milliseconds. That’s a relatively long time inside the center of a star, however, where nuclear reactions take place at much shorter timescales. Its longer survival than other isotopes means that 54calcium could play an outsize role in the reactions that create the heavy elements in the universe.
The discovery allows scientists to probe how interactions between protons and neutrons affect the energy gaps between shells and make nuclei more or less stable. “From the beginning of the field of nuclear structure physics, we were stuck with only being able to make detailed studies of the 350 or so stable isotopes—the ones we could dig out of the ground,” says Paul Cottle, a nuclear physicist at The Florida State University. “It has only been since the 1990s that we've been able to look carefully at some of the thousands of known short-lived radioactive isotopes. The big issue addressed in this experiment is developing a detailed understanding of how protons and neutrons talk to each other in nuclei.”
Scientists hope eventually to map the limits of stability and determine which nuclei can and can’t exist. “Scientifically, this is extremely interesting,” says Eric Scerri, a chemist and philosopher of chemistry at the University of California, Los Angeles. “The nuclear magic numbers are kind of giving way—the dogma begins to break down and the rules of the game have to be expanded. When you push things to a more extreme domain, new science comes out.”