Titanic calculations reveal nickel isotope is ‘doubly magic’

Physicists have demonstrated that nickel-78 is a doubly magic isotope – meaning it is exceptionally stable – using Titan, the most powerful supercomputer in the US. The results may improve our understanding matter’s stability.

Nuclei have individual shells with different energy levels. So-called magic numbers (2, 8, 20, 28, 50, 82 and 126) describe completely full shells, usually associated with highly stable isotopes. When the number of protons and neutrons are both magic numbers, the nucleus is doubly magic. These doubly magic nuclei have higher binding energies than their neighbours.

Nickel-58 is the most abundant of nickel’s isotopes and has 28 protons and just 30 neutrons. Nickel-78 with a whopping 50 neutrons is believed to be very stable and key in supernova nucleosynthesis of elements heavier than iron. However, nickel’s heaviest isotope is hard to prepare in a laboratory, mostly due to low yields. Scientists at the US Oak Ridge National Laboratory in Tennessee used Titan to calculate whether it was really stable and doubly magic. The simulations of all the possible energy configurations took approximately five million calculation hours.

The team claim that this is the first realistic calculation of the internal structure of nickel-78, and also the first evidence that the nucleus is doubly magic. Moreover, they found that the unusual stability of nickel-78 would even allow it to accept up to two extra neutrons without collapsing. The scientists now plan further computational exploration of heavier doubly magic nuclei like tin-100.