A team of nuclear physicists from the Washington University, St. Louis, Michigan State University, Western Michigan University and the University of Connecticut has created and characterized ‘featherweight’ oxygen — the lightest-ever version of the familiar oxygen, with only three neutrons to its eight protons. The results appear in the journal Physical Review Letters.

Oxygen is one of the most abundant elements in the Solar System, but oxygen-11 can be produced only in a laboratory.

It decays immediately after its creation by emitting two protons, and it can be observed solely through detection of its decay products.

Two-proton decay is the most recently discovered nuclear decay channel.

“What is most interesting to the nuclear physics community, however, is that oxygen-11 is the nuclear mirror of lithium-11, a very well-studied heavy isotope of lithium,” said Tyler Webb, a PhD candidate from the Department of Physics at the Washington University, St. Louis.

In nuclear physics, nuclei are said to be mirrors when one has a certain number of neutrons and protons and the other has a reversed amount, such as the 3:8 ratio of neutrons to protons in oxygen-11 as compared to the 8:3 ratio in lithium-11.

“When talking about mirror nuclei, we expect a sort of symmetry to hold,” Webb explained.

“The properties of a nucleus and its mirror should be similar: quantum states should be roughly close in energy relative to the nucleus’ ground state and the wave functions of those states should be similar.”

This symmetry can be stretched or broken, however.

Physicists can compare the actual structure of mirror nuclei against their expected structure to learn more about this important symmetry of atomic nuclei, the stuff that composes the visible matter of the Universe.

In this case, Webb and colleagues are most excited to compare lithium-11, which they know has two very loosely bound neutrons in a halo orbiting its core, to oxygen-11, which has two unbound protons.

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T. B. Webb et al. 2019. First Observation of Unbound 11O, the Mirror of the Halo Nucleus 11Li. Phys. Rev. Lett 122 (12); doi: 10.1103/PhysRevLett.122.122501