Nucleons are composed of a collection of quarks and gluons. Here is an artist's conception of a nucleon illustrated as its three basic quarks surrounded by a sea of quarks and gluons. GPDs will allow physicists to form a much clearer picture of the internal structure of a fast-moving nucleon - a snapshot of this structure at one instant in time.
Anatoly Radyushkin, a jointly appointed physics professor at Old Dominion University and senior scientist at Thomas Jefferson National Accelerator Facility, has been named a Virginia Outstanding Scientist of 2004. The award recognizes scientists who have made a recent contribution to basic scientific research that extends the boundaries of a field of science. Radyushkin is an internationally recognized nuclear theorist and a pioneer in the development of generalized parton distributions or GPDs. GPDs are a set of mathematical functions that are allowing physicists to, for the first time, obtain a 3-dimensional snapshot of the inner structure of the particles that make up the nucleus of the atom. This work is giving scientists a glimpse of the structure and dynamics of the basic building blocks of matter. In recognition of his work, the Science Museum of Virginia and the Office of the Governor named Radyushkin one of the recipients of Virginia's Outstanding Scientist and Industrialist Awards.
Radyushkin's work falls in the field of quantum chromodynamics (QCD). QCD is a fundamental theory that addresses the underlying structure of nucleons — the protons and neutrons that makeup the nucleus of the atom — in terms of their more elementary constituents. Nucleons are made up of quarks and gluons, elementary particles referred to as partons. Generalized parton distributions are functions that physicists can use to map out the location and momentum of the quarks and gluons inside a nucleon.
The functions are being developed with information obtained from electron-nucleon collisions. In this process, physicists use an accelerator to propel a beam of electrons to speeds approaching the speed of light. When these electrons strike a target, many collide with particles in the nuclei of atoms. Each collision results in an array of scattered particles. GPDs can be applied to those collisions that result in a scattered electron, proton and a photon, an effect called "deeply virtual Compton scattering." Applying GPDs to this scattering pattern reveals information about the structure of the nucleon before the collision. The result is an essentially holographic picture of the inner structure of the nucleon.
"GPDs allow scientists to use an accelerator to get the effective resolution power of an electron microscope and an X-ray installation," Radyushkin says. He says this work has opened a new field of scientific investigation that allows the measurement of the properties of protons and the comparison of these measurements with theoretical predictions. Experiments measuring and testing GPDs are conducted at Jefferson Lab, which is funded by the Department of Energy's Office of Science, and the testing of these methods are an essential part of JLab's present and future physics program.
Radyushkin completed his pre-doctoral work at Moscow State University in the Russian Federation, and received his Ph.D. in physics there in 1978. He is a permanent staff member of the Laboratory of Theoretical Physics in Dubna, Russia. He came to Virginia in 1991 as a visiting senior scientist at Jefferson Lab. Since 1992, he has split his time as a full professor of physics at Old Dominion University in Norfolk, Va., and senior staff scientist at Jefferson Lab. Radyushkin is an author or co-author on 90 journal papers in his field, which have been referenced in more than 4,400 other publications. He is a member of the American Physical Society and was elected a Fellow of the Society in 1996.
Radyushkin and the six other Outstanding Scientists and Industrialists will be introduced to the Virginia Commonwealth General Assembly March 2. The honorees will receive their award medallions at a black-tie banquet at the Science Museum of Virginia March 30.