  We propose to search for neutron halo isomers populated via $\gamma$-capture
in stable nuclei with mass numbers of about A=140-180 or A=40-60, where the
$4s_{1/2}$ or $3s_{1/2}$ neutron shell model state reaches zero binding energy.
These halo nuclei can be produced for the first time with new $\gamma$-beams of
high intensity and small band width ($\le$ 0.1%) achievable via Compton
back-scattering off brilliant electron beams thus offering a promising
perspective to selectively populate these isomers with small separation
energies of 1 eV to a few keV. Similar to single-neutron halo states for very
light, extremely neutron-rich, radioactive nuclei
\cite{hansen95,tanihata96,aumann00}, the low neutron separation energy and
short-range nuclear force allows the neutron to tunnel far out into free space
much beyond the nuclear core radius. This results in prolonged half lives of
the isomers for the $\gamma$-decay back to the ground state in the 100
ps-$\mu$s range. Similar to the treatment of photodisintegration of the
deuteron, the neutron release from the neutron halo isomer via a second,
low-energy, intense photon beam has a known much larger cross section with a
typical energy threshold behavior. In the second step, the neutrons can be
released as a low-energy, pulsed, polarized neutron beam of high intensity and
high brilliance, possibly being much superior to presently existing beams from
reactors or spallation neutron sources.
