Nuclear Reactions

Our group studies nuclear reactions to provide insight into the mechanism of nuclear fusion reactions.  Currently, experiments worldwide are trying to discover the next new element, which will likely be element 120.  Previous experiments relied on using the very neutron-rich isotope 48Ca as a projectile, but element 120 will require a heavier projectile because of a lack of appropriate targets.  This product will be near the predicted closed shells at Z = 120 and N = 184.  As an analog for these very challenging experiments, we are studying the production of nuclides near the Z = 82 and N = 126 shells, which have much higher production cross sections.  We have measured excitation functions for the reactions of 44Ca, 48Ca, 45Sc, and 50Ti and 54Cr projectiles with lanthanide targets.  In addition, we have developed a simple theoretical model that describes the experimental data well. The results suggest that the production of new elements with projectiles heavier than 48Ca will be heavily suppressed because of two effects: a significant decrease in the probability of forming the compound nucleus, and a significant decrease in the probability that the compound nucleus will survive against fission.  This work is helping to guide the discovery of new elements worldwide. Our future work will focus on producing deformed nuclei, because the deformation of a nucleus substantially affects its likelihood of survival, and we want to investigate this effect further.

This type of research can broadly be described as physical chemistry of nuclei. Chemists working on these experiments learn about radiation detectors, magnetic separators, data acquisition systems, target fabrication, and the use of particle accelerators. Students learn how to do complex data analyses while employing statistical mechanics to model the reaction mechanism.