not talking about the virtuous kind, or the popular video game.
Instead, the halo that three scientists were working with was in fact
a halo nucleus. Thomas Papenbrock, associate professor at the
University of Tennessee, Knoxville, Gaute Hagen from Oak Ridge
National Laboratory, and Morten Hjorth-Jenson from the University of
Olso recently calculated the 'halo' of such nuclei, in terms of
physics. Their report was published earlier this month in Physical
Review Letters, titled "Ab-initio computation of the 17F
proton-halo state and resonances in A = 17 nuclei."The
atom fluorine-17 was used, because it is in fact a 'mirror nucleus'
of oxygen-17. Where fluorine-17 has nine protons and eight neutrons,
oxygen-17 has eight protons and nine neutrons. These two atoms
surround oxygen-16: the most abundant and stable isotope of oxygen.
By exciting a proton found orbiting around a fluorine-17, a halo is
formed. This proton is far away from the oxygen-16 core.A
halo nucleus is defined as a nucleus that, because of weak forces,
has its nucleons (protons or neutrons, normally found within the
nucleus) pushed away from the center. These nucleons then form a sort
of halo. One of the challenges the scientists faced was the fact that
halo nuclei only live for a few milliseconds and are very fragile.
Moreover, one could find halo nuclei at the far end of the nuclear
existence spectrum (the dripline), where a slight imbalance between
protons and neutrons means that the nucleus will fall apart.Because
there were more than two bodies interacting in this system,
calculations proved difficult to pinpoint the exact numbers. This
called for sophisticated methods when working with the 17 interacting
particles in the isotope, titled many-body problems. The team, at
first, employed a nuclear Hamiltonian, which reads the energy of the
system regarding its momentum and coordinates. Then, a numerical
method, known as the coupled-cluster method, which calculates the
proton halo state in fluorine-17 by solving the many-body
problems. All this was done on the Oak Ridge
National Laboratory's super-computer Jaguar. Impressive,
considering the calculations reflect a similar value for
the binding energy compared to experimental data, as well
as no adjustable parameters.Scientists hope that the
increased knowledge of nuclei will lead them to discover the limits
of nuclear existence. By investigating the nucleus, applications can
be made to all aspects of life, such as medicine or space travel.