Гелий-9

HELIUM-9 GROUND STATE OBSERVED. Making superheavy
new elements is difficult since just any old number of neutrons and
protons will not necessarily result in a stable nuclear architecture.
The same is true for producing exotic forms of light nuclei. The
main form of helium consists of two neutrons and two protons.
But heavier, more tenuous, versions can be built amid collisions at
particle accelerators. An extreme example is He-8, thought to
consist of a He-4 core surrounded by a halo of four additional
neutrons. Nature seldom gives one the chance to examine
neutronic matter separate from protons, so the study of "halo
nuclei" has become one of the hot areas of nuclear physics. Now
in an experiment at the National Superconducting Cyclotron Lab
(NSCL) at Michigan State University, physicists have glimpsed
the ground state of an even rarer isotope for the first time. By
shooting a beam of Be-11 nuclei into a target of Be-9 atoms, the
researchers deduce that a He-8 nucleus moving through the lab
with a co-moving neutron can confederate weakly and briefly
(only for 10^-20 seconds) to form a He-9 nucleus. In this case one
can think of the last neutron as constituting a second halo outside
an inner 4-neutron halo.