Towards describing atomic nuclei beyond the drip line

The study of atomic nuclei at the limit of their existence is an important topic in experimental and theoretical nuclear physics. Nuclei with many more neutrons than protons have their last few neutrons barely bound to the core of the nucleus. Those nuclei are characterized as almost neutron-unbound or as being located near the "neutron drip line". In the chain of oxygen isotopes, Oxygen-24 with 16 neutrons and 8 protons is the Oxygen isotope with the largest number of nucleons whose lowest energy level–the ground state–cannot decay by emission of a neutron. The oxygen isotopes with more neutrons are said to lie beyond the neutron drip line since neutrons are emitted–or "drip off"–even if the system is in its ground state. Still, their existence can be seen in experiments as a very short-lived resonance state which exists for less that 10-20 seconds. In nuclei approaching the drip line, excited neutron-unbound states decay by emission of a neutron and coexist with bound states.

Alexander Volya from Florida State University and NSCL's Vladimir Zelevinsky have developed a new version of the "Continuum Shell Model". This theoretical model simultaneously describes the energies as well as the lifetimes of excited states against the neutron decay for all states shown in Figure 1 – neutron-bound and neutron-unbound states within the same model.

Figure 1: Neutron-bound (black lines) and neutron-unbound states (yellow and red) which are described by the new Continuum Shell Model by Volya and Zelevinsky. more

Reference
Alexander Volya and Vladimir Zelevinsky, Phys. Rev. Lett. 94 (2005) 052501.

Contact
Vladimir Zelevinsky
Zelevins at nscl.msu.edu