Glenn T. Seaborg Award For Nuclear Chemistry

On his departmental Web page, Lee G. Sobotka, 54, professor of chemistry and physics at Washington University in St. Louis, describes his research focus as “understanding, detecting and innovative uses of God’s Quantum Dots.” Those who nominated the award winner get more down to Earth when describing his development of novel technologies to attack important and difficult problems in basic nuclear science.

For example, Sobotka and D. G. Sarantites developed the Dwarf-Ball and Dwarf-Wall devices that allowed the first measurement with full 4π coverage for the emitted charged particles, for example, protons, deuterons, tritons, and α particles, that didn’t require forfeiting the ability to measure photons or neutrons in a surrounding device. This accomplishment required Sobotka to advance both detector technology and signal-processing electronics.

Another example resulted from his recognition that the existing microcircuits built on Si chips for analog pulse-processing designed for high-energy physics applications did not have the necessary features for their work. Sobotka and coworkers Jon Elson and George Engel set to work making some that did. These microelectronics facilitate the operation of 1,000+ element Si arrays for the detection of ionizing radiation. This technology enabled Sobotka and his close collaborator Robert Charity to perform many-particle correlation experiments and thereby study the continuum structure of light nuclei by particle-decay spectroscopy. This includes, for example, the continuum structure or resonances of very exotic nuclei such as ¹⁰C and, he reports most recently, ⁸C. Half a dozen groups around the world are gearing up to use this technology.

These successes motivated Sobotka’s team to develop another generic chip for pulse-shape analysis, one with the ability to tell the type of impinging radiation as well as its energy for certain scintillators. Although this chip is still undergoing testing, groups at Michigan State University and Los Alamos National Laboratory are planning to use it for basic nuclear science experiments and for homeland security applications, respectively.

Sobotka also has a long-standing interest in the density of states (DoS) of the nuclear “quantum dot.” His interest focuses on how the DoS increases with excitation energy and is affected by the neutron-proton asymmetry with the attendant change in the in-medium (nucleon-nucleon) correlations with changing neutron-to-proton ratio.

Sobotka received a bachelor’s degree in chemistry from the University of Michigan in 1977 and a Ph.D. in chemistry from the University of California, Berkeley, in 1982. After a postdoctoral stint at UC Berkeley, he joined the faculty of Washington University in St. Louis in 1984 and has made it his professional home.

A colleague sums up Sobotka’s attributes: “While many scientists meld technology, experimentation, and nuclear modeling, Sobotka has spliced these together to an unrivaled degree. He attributes this to a mind-set of doing what has to be done, when it has to be done, with the resources one can realistically expect to have, while engaging like-minded collaborators who enjoy, as he does, all aspects of the science of discovery.”

Sobotka will present the award address before the Division of Nuclear Chemistry & Technology.