Physical Sciences
Atomic Shape-Shifters The Three Shapes of Stable Nickel-64 Nuclei
By Maddy Stratton
T
he atom remains a mysterious component of reality which modern scientists continue working to understand. Strange phenomena start to occur when analyzing these tiny units of matter—only certain amounts of energy are allowed, one electron can be found in several places at once, and overall, chaos ensues. This leaves scientists pondering how they can approach learning more about the strange world of the atom. For starters, researchers can model the atom in different ways to investigate its properties. The models themselves evolve over time as new information is discovered. J. J. Thomson’s 1904 representation argued the atom consisted of a positively-charged nucleus “soup” with drops of negative charge interspersed to make it look like a plum pudding (the model was appropriately named the “Plum Pudding Model”).1 As researchers continued to learn more about the structure of the atom—namely, that it resembles a sphere, consists of a positively-charged nucleus made up of two types of tiny particles (protons and neutrons), which is orbited by even tinier, negatively-charged particles called electrons—the atomic model changed even further (Figure 1). Today, it is changing again, right now, for nickel-64 (Ni-64). Robert Janssens, working alongside his team at UNC’s Triangle Universities Nuclear Laboratory (TUNL) and three other nuclear laboratories, has established the existence of three distinct shapes of the stable Ni-64 isotope.2
“There seems to be an aspect of the nuclear force that isn’t yet understood which shows up in neutron-rich nuclei.”
Janssens’s interest in nuclear physics stems from his experience as an undergraduate at the Catholic University of Louvain in Belgium. During his time there, the university was overseeing the construction of a cyclotron, a particle accelerator. Always showing interest in nuclear structure and reactions, Janssens aided in the construction of the accelerator and was inspired to write his thesis in the same domain of nuclear physics during his senior year.3 He gained a PhD in experimental nuclear physics in Louvain before taking Figure 1: Adding or removing neutrons to/from an atom creates an a postdoctoral position in isotope of that atom. Adding/removthe Netherlands. Then, he ing protons creates a new element. moved to the United States. Today, he and his team of researchers are studying Ni-64 nuclei. Atoms of the same element (which is determined by their number of protons) with differing amounts of neutrons are isotopes of that element. Usually, the nickel atom has 30 neutrons inside its nucleus. Ni-64, however, has 36. This particular isotope of nickel, though less abundant in nature, has stable properties which makes it easier to study in the lab. Janssens’s team and collaborating labs have identified three distinct shapes of stable Ni-64 nuclei, which appear as energy is added to the atom. Specifically, as energy increases, the nuclear shapes resemble the typical sphere (the ground state), a flattened shape, and an elongated football shape [Figure 2].4 These changes in
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