Hope College Department of Physics and Engineering
Research Experiences for Undergraduates
Project Title: Understanding the Nuclear Structure of 8 Li with a Radioactive Nuclear Beam
Student Name: Carol J. Guess
Student's home institution: Hope College
Research Advisor(s): Dr. P. A. DeYoung, Dr. G. F. Peaslee
Source of Support: NSF-RUI
Collaborators: Dr. E. F. Aguilera, Dr. J.J. Kolata
8 Li is one of many unstable nuclei not abundant in nature. Structural knowledge of these unstable nuclei is important to determine the history of the early universe. The purpose of this experiment was to determine whether 8 Li has a uniform nuclear mass density. A nonuniform mass distribution often signifies the presence of a halo, which affects reaction properties.
A beam of 8 Li collided with a 208 Pb target and fused to form 216 At * , a very unstable compound nucleus. It decayed immediately by neutron evaporation due to its high energy and angular momentum, emitting from 2 to 5 neutrons. At the studied energies of 36 – 42 MeV, 211 At and 212 At were formed. 212 At ended in both its ground and metastable states. 211 At radioactively decayed with alpha emissions of 6.0 and 7.5 MeV, while 212 At decayed with alpha emissions of 7.6 and 7.8 MeV. The beam was cycled on and off, because while the beam was off only decay products were emitted from the target chamber. This greatly improved detection of the desired alphas.
Cross sections were calculated accounting for beam structure. The amount of metastable 212 At formed increases with energy, due to the higher initial angular momentum. The total cross sections were found to be about 100 millibarns lower than predicted. This could be due to incomplete fusion of 8 Li and 208 Pb.
Future research plans include measuring the elastic scattering cross section to find an experimental total reaction cross section. This will constrain our calculations, and the fusion cross sections will be interpreted within those results.
Publications and Presentations:
“Hindrance of Complete Fusion in the 8Li+208Pb System at Above-Barrier Energies.” E.F. Aguilera, E. Martinez-Quiroz, P. Rosales, J.J. Kolata, P.A. DeYoung, P.J. Mears*, C. Guess*, F.D. Becchetti, J.H. Lupton, and Yu Chen. Phys. Rev. C 80, 044605 (2009).
“Protons from 8B+58Ni.” E.f. Aguilera, E. Martinez-Quiroz, H. Garcia-martinez, D. Lizcano, J.J. Kolato, L.O. Lamm, G. Rogachev, P.A. DeYoung, C. Guess*, U. Khadka*, P.J. Mears*, F.D. Becchetti, Y. Chen, H. Jiang, J.D. Hinnefeld, and G.F. Peaslee. Revista Mexicana de Fisica 52, 41 (2006).
“Two-neutron Transfer in the 6He+209Bi Reaction Near the Coulomb Barrier.” P.A. DeYoung, P.J. Mears*, J.J. Kolata, E.F. Aguilera, F.D. Beccetti, Y. Chen, M. Cloughesy, H. Griffin, C. Guess*, J.D. Hinnefeld, H. Jiang, Scott R. Jones, U. Khadka*, D. Lizcano, E. Martinez-Quiroz, M. Ojaniega, G.F. Peaslee, A. Peña*, S. VanDenDrieddshe, and J. Zimmerman. Phys. Rev. C 71, 051601 (2005).
“Understanding the Nuclear Structure of 8Li with a Radioactive Nuclear Beam.” Carol J. Guess*, P.A. DeYoung, G.F. Peaslee, E.F. Aguilera, E. Martinex Quiroz, J.J. Kolata, and J.D. Hinnefeld. Poster CK.025. Division of Nuclear Physics Fall Meeting. Chicago IL, October 2004