Atomic nuclei make up more than 99% of the matter we see in the Universe. From the possible 6000 nuclei that are predicted to exist, only 283 are stable, whereas, about 2000 short-lived ones have been synthesized to date. The study of these rare isotopes offers the opportunity to elucidate the nucleon-nucleon interaction, as well as the various nucleosynthesis processes in the stars. Reaching the limits of nuclear stability, especially the neutron-rich side ('neutron-drip' line), is challenging and requires powerful techniques and facilities.
Neutron-rich nuclei are typically produced by fission or projectile fragmentation. At the Cyclotron Institute (CI) of Texas A&M University, we explored a novel production approach based on peripheral collisions of neutron-rich beams on heavy neutron-rich targets in the energy range of 25 MeV/nucleon [1]. This approach provides an efficient way to access nuclei towards the neutron drip-line.
Concurrently, we studied the process of chemical (N/Z) equilibration between the reaction partners of peripheral collisions in this energy range, employing a recently developed experimental approach based on the isoscaling technique [2]. The motivation of these studies is the possibility to extract information on the properties of the nuclear effective interaction (via comparisons with microscopic transport models) as manifested in the mechanism of nucleon exchange during the process of N/Z equilibration. We have performed detailed calculations using the code CoMD (Constrained Molecular Dynamics) of A. Bonasera and M. Papa [3]. The code implements an appropriate effective interaction with several forms of the density dependence of the nucleon symmetry potential (symmetry energy) and imposes the Pauli principle at each time step of the collision via a phase-space constraint.
Finally, we explored the symmetry energy of hot neutron-rich nuclei [4] with the aid of the Statistical Multifragmentation Model. The properties of hot nuclei in dense environments are of great importance for astrophysical modeling (e.g., supernovae [5]). The talk concludes with the experimental perspectives offered by neutron-rich rare beams from existing and upcoming radioactive beam facilities in Europe, USA, Japan and other places.
[1] G.A. Souliotis et al., Phys. Rev. Lett. 91, 022701 (2003)
[2] G.A. Souliotis et al., Phys. Lett. B 588, 35 (2004)
[3] M. Papa, A. Bonasera et al., Phys. Rev. C 64, 024612 (2001)
[4] G. A. Souliotis et al., Phys. Rev. C 75, 011601 (2007)
[5] A.S. Botvina and I.N. Mishustin, Phys. Lett. B 584, 233 (2004)
Speaker: G. A. Souliotis
Assistant Professor, Laboratory of Physical Chemistry, Department of Chemistry, National and Kapodistrian University of Athens
Time: Monday, 18 January 2010, 13:00