Evidence for α-particle condensation in nuclei from the Hoyle state deexcitation, A. R. Raduta, NIPNE-Bucharest, Romania − Heavy ion reactions induced by few tens MeV/nucleon beams constitute an ideal framework for producing and studying nuclear excited states close to the decay threshold.  The fragmentation of quasi-projectiles from the nuclear reaction ⁴⁰Ca+¹²C at 25 MeV/nucleon performed at LNS-Catania was employed in order to populate the Hoyle state of ¹²C and investigate the theoretically predicted molecular structures.  Complete kinematic characterization of individual decay events, made possible by the CHIMERA high-granularity 4π charged particle multi-detector, reveals that 7.5±4.0% of the particle decays of the Hoyle state correspond to direct decays in three equal-energy α-particles and thus fulfill the decay criteria of an α-particle condensate.   Moreover, events with increased kinetic energy dispersion in the ¹²C center of mass, which amount to 9.5±4.0%, point toward the occurrence of a second competing molecular configuration, this time of a linear α-chain type.  Both α-particle condensate and linear chain structures have been theoretically predicted but, to our knowledge, not experimentally confirmed so far [1,2].

[1] Ad. R. Raduta et al., Phys. Lett. B705, 2011, 65.

[2] Ad. R. Raduta et al., Int. J. Mod. Phys. E20, 2011, 902.