Introduction
Nuclear halo states are one of the more fascinating phenomena discovered in
the spectrum of light nuclei. They occur close to the neutron drip lines as a
threshold phenomenon when one or more weakly bound nucleons tunnel into the
surrounding space. The general structure of these halo states is by now almost
generally understood, but the precise role of intruder states and pairing in the
continuum still needs to be discussed theoretically and experimentally. The
existence of halo states has important consequences for the continuum spectra of
such nuclei. This continuum can be probed in lowenergy reactions important in
astrophysics, or in breakup reactions of halo projectiles. A great deal more
work is needed to understand the manybody continuum of twonucleon halo
systems. Here, it will be instructive to examine the isospin analogue, namely
twoproton radioactivity in nuclei in the vicinity of the proton dripline.
Possible proton halo states are also under discussion now.
Experimental probing of halo states continues to be obtained from more
precise breakup and particle transfer reactions, and supplements the
measurements of size, of momentum distributions of fragments, and of beta decays
to or from halo states. Most recently, the kinematicallycomplete measurements
of breakup reactions is leading to a new experimental wealth of information on
structures in the continuum of halo nuclei, including Borromean continuum.
Details of twoneutron correlations and coreexcited states have been measured,
challenging both halo structure models and theories of reaction dynamics.
It is therefore necessary to combine present and future theoretical
capabilities with detailed and accuratelyspecified experimental observations.
The aim of the planned workshop is therefore to gather theorists, and
experimentalists with a flair for theory, to take the measure of current and
future progress in this field.
This workshop is a natural followup of the previous workshops help in 1996
and 2001 with the same title and the same organisers. These were judged by both
the theory and experimental participants to provide most instructive, fruitful
and informal meeting grounds for the detailed discussion of all the necessary
issues. Since we see that much has developed in the five years since the last
meeting, a successor workshop should prove similarly beneficial.
