level 2

Science Alliance Annual Report

2008–2009

UT-ORNL Joint Institutes

Joint Institute for Heavy Ion Research

Stable atomic nuclei maintain specific neutron-to-proton ratios; if they do not, the nuclei experience some level of instability. Slightly less than 300 proton-neutron combinations are stable enough to exist permanently in nature. Thousands more can be synthesized by scientists or created in the stars. But these heavy, exotic nuclei, with too many neutrons or protons to be stable, quickly give off electrons or positrons until they reach more stable arrangements.

Scientists create the new, superheavy elements by fusing lighter nuclei. But their existence is brief. The new nuclei heat up and must find a way to cool back down to a stable state. Often, to do so, they simply break apart through fission.

The Joint Institute for Heavy Ion Research supports work in this fascinating area of physics. Their programs supply critical research assistance and manage dormitory facilities for scientists visiting the ORNL Holifield Radioactive Ion Beam Facility. In spite of recent progress, it’s still a challenge to find the optimal combination of beam and target as well as other conditions to maintain the structural integrity of superheavy nuclei long enough to fuse into new elements at rates that can be measured experimentally. This is due in part to the relationship between the barriers to fission, which stabilize the nucleus, and excitation energy, i.e. the energy difference between the excited state produced by fusion and the ground (stable) state.

Groundbreaking calculations by JIHIR scientists J.C. Pei, Witek Nazarewicz, J.A. Sheikh and A.K. Kerman show that even superheavy nuclei receive a little protection from the electric field produced by the nucleus. The results, consistent with recent experimental data, offer clues to the conditions for creating new elements and provide a wider context for understanding other types of fission, such as that used in reactors to supply energy. Their work should help to establish the mass and charge limits in producing and studying atomic nuclei.

Carrol Bingham serves as JIHIR director; Witek Nazarewicz is the Holifield Facility’s scientific director. Both are professors in UTK physics and astronomy. A $500,000 addition to the JIHIR building was dedicated in February 2009 during the Japan-U.S. Theory Institute for Physics with Exotic Nuclei (JUSTIPEN) workshop.