Hwang wins award for resonance theory

Even though Richard Hwang officially retired in 2003, the chalkboard in his office is still cluttered with equations, and piles of old dot matrix printouts stand on top of filing cabinets next to pictures of his grandchildren.

Hwang is tying up the loose ends of a successful 40-year career in nuclear reactor physics, a career that was honored by his selection as the 2004 Eugene P. Wigner Award winner. The award is the American Nuclear Society's highest honor for a reactor physicist.

“ I couldn't expect a better retirement gift,” he said of the award. “It's what everyone who works in this field strives for.”

The Wigner award, given by the American Nuclear Society for “outstanding achievements in the field of nuclear reactor physics,” recognizes Hwang's work on neutron resonance theory, a body of theory that helps nuclear engineers build computer models to predict the complicated behavior of neutron-induced reactions inside a nuclear reactor.

Neutrons are the particles that sustain nuclear reactions within a reactor core. When an atom splits, it releases one or more fast-moving neutrons, which subsequently collide with other atoms causing them to split, producing still more neutrons. In a reactor, this chain reaction is moderated so the rate of neutron absorption balances the rate of neutron production.

Using accelerators, physicists have collected neutron cross section data that describe the likelihood that a neutron passing close to a target nucleus will collide or react with that nucleus. However, scaling this information to the macroscopic world of nuclear reactors involves calculations of great complexity, Hwang said. “You have to consider macroscopic factors like the elemental composition of the core, the reactor lattice configuration and temperature.”

Hwang developed mathematical treatments that convert fundamental neutron data — the “microscopic information” from cross section measurements — into a processed form that nuclear engineers can use in their reactor-scale computer models. Ultimately, those models are used to evaluate reactor safety and design new, more efficient reactors.