Neutrons Play the Lead to Protons in Dance around “Double-Magic” Nucleus

Electric and magnetic properties of a radioactive atom provide unique insight into the nature of proton and neutron motion.

The Science

An exotic, radioactive beam of tellurium (¹³⁶Te), traveling at 8 percent of the speed of light, was created and studied by scientists at Oak Ridge National Laboratory to explore the nature of protons and neutrons, nature’s building blocks. They picked the tellurium because of how its protons and neutrons are organized. Radioactive ¹³⁶Te possesses two protons and two neutrons outside of an extremely stable, a.k.a. “double-magic,” core. The tellurium provides a unique laboratory for exploring the nature of neutron and proton motion. The team found that two neutron and proton pairs in the exotic nucleus dance around the inactive core but on unequal footing. There are many possible dance formations for a neutron and proton pair but the neutrons are curiously more active.

The Impact

This study resolved discrepancies in state-of-the-art calculations that describe the nature of proton and neutron motion. It further resolved questions of models showing the interactions within atomic nuclei. This work paves the way for a more accurate understanding of these building blocks of nature.

Summary

Atomic nuclei are finite many-body quantum systems that exhibit increased stability or “shell structure” when the proton and/or neutron numbers equal 2, 8, 20, 28, 50, 82, or 126. If both the proton and neutron numbers are equal to one of these “magic” values, the nucleus is said to be “double magic.” Atomic nuclei with just a few protons or neutrons outside of these stable cores provide a simple and unique laboratory for exploring the nature of neutron and proton motion. Radioactive ¹³⁶Te, which possesses two protons and two neutrons outside of an inert “double-magic” ¹³²Sn core, is such an example. Scientists at Oak Ridge National Laboratory in Tennessee created an exotic, radioactive beam of ¹³⁶Te. They found that two neutron and proton pairs in the exotic nucleus dance around an inactive ¹³²Sn core but on unequal footing. They made this finding using a novel technique that measures both electric and magnetic properties of radioactive nuclei. The measurements are a powerful and sensitive tool to test and resolve discrepancies in state-of-the-art theoretical models. The results indicate that the simple two proton and two neutron system, around the double magic core, is prolate (shaped like an American football) deformed and that the underlying structure is dominated by neutron motion. The understanding of proton and neutron motion within atomic nuclei is an ever-evolving topic, and the advent of accelerated beams of exotic nuclei has led to many surprises as scientists strive to develop a more accurate understanding of the proton and neutron building blocks of nature.

Contact

James Mitchell Allmond
Physics Division, Oak Ridge National Laboratory
[email protected]

Funding

This material is based upon work supported by the U.S. Department of Energy (DOE), Office of Science, Office of Nuclear Physics, under contract DE-AC05-00OR22725, and this research used resources of the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory, which was a DOE Office of Science user facility. This research was also sponsored by the Australian Research Council under grant DP0773273, by DOE under contract DE-FG02-96ER40963, and by the National Science Foundation, grant PHY-1404442.

Publications

J.M. Allmond, A.E. Stuchbery, C. Baktash, A. Gargano, A. Galindo-Uribarri, D.C. Radford, C.R. Bingham, B.A. Brown, L. Coraggio, A. Covello, M. Danchev, C.J. Gross, P.A. Hausladen, N. Itaco, K. Lagergren, E. Padilla-Rodal, J. Pavan, M.A. Riley, N.J. Stone, D.W. Stracener, R.L. Varner, and C.H. Yu, “Electromagnetic moments of radioactive ¹³⁶Te and the emergence of collectivity 2p⊕2n outside of double-magic ¹³²Sn.” Physical Review Letters 118, 092503 (2017). [DOI: 10.1103/PhysRevLett.118.092503]