My research in nuclear chemistry is focused on studying the dynamics of heavy ion reactions over a wide range of energies. While heavy ion reactions have been studied for many years using beams of stable isotopes, the NSCL provides a unique opportunity to explore these reactions with radioactive ion beams (RIBs). These radioactive isotopes can have exotic properties such as neutron skins, halos, or unexpected changes in the shell structure. I am interested in how these exotic properties manifest themselves in heavy ion collisions, specifically fusion reactions.
At energies around the Coulomb barrier, we will study the probability (or cross section) for the fusion of the heavy ions. Heavy-ion fusion has a historic role in the field of chemistry as it is the only known mechanism for producing the heaviest elements of the periodic table. The new ReA3 facility will allow for the RIBs produced at the NSCL to be stopped and reaccelerated at conditions suitable for fusion reactions. Surprisingly, only three fusion experiments with RIBs between the fluorine and tin isotopes have ever been completed. ReA3 will allow us to begin to explore heavy ion fusion with a new arsenal of beams. We plan to examine the possible enhancement and hindrance of fusion due to the exotic properties of the RIBs as well as investigate the quasifission mechanism which hinders the production of super-heavy elements.
Currently, the construction of a fission fragment detector is one of the main activities in the group. In relatively heavy systems the compound nucleus formed from the fusion of the heavy ions will decay dominantly through the fission process. Thus we can measure the probability of fusion by counting the number of times fission occurred. The setup, as shown in the figure, will consist of four large area gas filled detectors called PPACs which will provide high efficiency and precision for measuring fission fragments.
At higher energies (well beyond the Coulomb barrier), heavy ion collisions can be used to explore the nuclear equation of state (EoS). Like any material, nuclear matter has an EoS which relates properties such as pressure, density, internal energy, and temperature to each other. Heavy ion collisions allow us to create and study nuclear matter at different densities, temperatures, and pressures. We want use RIB induced reactions to investigate how the EoS depends on the neutron-to-proton ratio of the nuclear matter. Future plans include using the Modular Neutron Array (MoNA) and the superconducting Sweeper magnet at the NSCL to measure the emission of neutrons in coincidence with heavy charged particles from reactions induced with RIBs. The results from the experiment compared with theory should provide new insight into the nuclear EoS.
Mechanical design rendering of the fission detector setup. The radioactive ion beam enters from the left (white arrow) and travels through the micro-channel plate timing detector (MCP) and impinges on a target. Fission fragments resulting from the fusion of the projectile and target will be detected in the four large area Parallel Plate Avalanche Counters (PPACs).
Near-barrier reactions with radioactive ino beams at the ReA3 facility. Z. Kohley. EPJ Web of Conferences 63, 02003 (2013).
Heavy-ion Collisions: Direct and indirect measurements of the density and temperature dependence of Esym. Z. Kohley, S.J. Yennello. Eur. Phys. J. A 50,31 (2014)
Exploiting neutron-rich radioactive ion beams to constrain the symmetry energy. Z. Kohley, G. Christian, T. Baumann, P.A. DeYoung, J.E. Finck, N. Frank, M. Jones, J.K. Smith, J. Snyder, A. Spyrou, M. Thoennessen. Phys. Rev. C 88, 041601(R) (2013).
Study of two-neutron radioactivity in the decay of 26O. Z. Kohley, T. Baumann, D. Bazin, G. Christian, P. A. DeYoung, J. E. Finck, N. Frank, M. Jones, E. Lunderberg, B. Luther, S. Mosby, T. Nagi, J. K. Smith, J. Snyder, A. Spyrou, M. Thoennessen. Phys. Rev. Lett. 110, 15201 (2013).
Unresolved Question of the 10He Ground State Resonance. Z. Kohley, J. Snyder, T. Baumann, G. Christian, P. A. DeYoung, J. E. Finck, R. A. Haring-Kaye, M. Jones, E. Lunderberg, B. Luther, S. Mosby, A. Simon, J. K. Smith, A. Spyrou, S. L. Stephenson, M. Thoennessen. Phys. Rev. Lett. 109, 232501 (2012).