Alpha-particle condensation in nuclei

A round up of the present status of the conjecture that nα nuclei form an αparticle condensate in excited states close to the nα threshold is given. Experiments which could demonstrate the condensate character are proposed. Possible lines of further theoretical developments are discussed. In this article we want to report on the present status of our recent conjecture [1] that at least light nα-nuclei may show around the threshold for nα disintegration, bound or resonance states which are of the α-particle gas type, i.e. they can be characterised by a self-bound quite dilute gas of almost unperturbed α-particles, all in relative s-states with respect to their respective center of mass coordinates and thus forming a Bose condensed state. Such a state is quite analogous to the recently discovered Bose condensates of bosonic atoms formed in magnetic traps. Also there the Bose condensate is characterised by all Bosons occupying the lowest s-wave state of the mean field potential. Of course, in the atomic case the number of atoms can be enormous whereas in the nuclear case we, so far, only consider a handfull of α-particles. However, as soon as n 1, one can expect condensation characteristics and therefore relatively few α’s may be sufficient. The situation is similar to nuclear pairing where also a very limited number of Cooper pairs are involved and yet most nuclei manifest clear signatures of superfluidity. Let us shortly repeat what led us to our conjecture. It is well known that the only nucleus which shows a well developed α-particle structure in its ground state is Be. This singular feature was probably not given the attention it desserves. Other nuclei with three, four, ...,nα-particles collapse in their groud states to a much denser system where the α-particles strongly overlap and probably loose almost totally their identity (see, however discussion below). It seems a very natural