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78Ni – doubly magic, extremely neutron rich, but still away from the edge

UT-ORNL physicists compute the structure of the rare nucleus 78Ni
October 27, 2016

UT and Oak Ridge National Laboratory (ORNL) nuclear physicists computed the exotic nucleus 78Ni (consisting of 28 protons and 50 neutrons). Availing themselves of Titan, the powerful supercomputer at ORNL, Gaute Hagen, Gustav Jansen, and Thomas Papenbrock computed the structure of the rare isotope nickel-78 and found that it is, in the terminology of nuclear physics, “doubly-magic.”

The term describes the arrangement of nucleons—protons or neutrons—in the shells of a nucleus. When present in certain “magic” numbers: 2, 8, 20, 28, 50, 82, and 126, they make the nucleus more strongly bound. In doubly-magic nuclei, both the protons and neutrons appear in magic numbers.

Atomic nuclei can be quite fragile, particularly rare isotopes that live for only fractions of a second before they undergo beta decay. This is the territory where nickel-78 resides, along with other isotopes of oxygen, calcium, and tin, for example, which have been the object of previous studies. Researchers suspected that nickel-78 is doubly-magic, and the work of the UT-ORNL team was the first realistic ab initio computation to confirm that’s the case. The results were presented in the paper “Structure of 78Ni from First-Principles Computations,” published in Physical Review Letters. They also found that its neighbor, nickel-80, is still held together by the strong force, thus putting the neutron drip line beyond neutron number 52 for nickel. The theoretical predictions await experimental verification.

Nuclear science has a standing interest in understanding how rare isotopes are structured and applying those findings to fields including materials science and nuclear medicine. Rare isotopes are also important for understanding astrophysics. In fact, nickel-78 is in the region of the r-process (or rapid neutron capture) path: the phenomenon by which the death of a supernova could lead to the formation of heavy elements like uranium and gold.

From left, Oak Ridge National Laboratory’s Gaute Hagen, Thomas Papenbrock and Gustav Jansen used the Titan supercomputer at the Oak Ridge Leadership Computing Facility to calculate the structure of doubly magic nickel-78 and its neighbors. Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; photographer Jason Richards.

Hagen, Jensen, and Papenbrock bring together the expertise and equipment of the national laboratory and the university to investigate this area in the chart of the nuclides. Papenbrock is a professor in the department and Hagen is staff at ORNL and an adjunct assistant professor. Jensen, a former postdoc with UT Physics, is staff at ORNL. Their earlier studies showed that calcium-52 defies expectations for a supposedly doubly-magic nucleus.

To read more about their latest work with nickel isotopes, please visit the ORNL website.

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