May 16, 2012
American Center for Physics
College Park, MD
Date: Wednesday, May 16, 2012
Speaker: James J. (Jeff) Carroll, US Army Research Laboratory (ARL)
Topic: Ups and Downs of Nuclear Isomers
Time and Location: 1:00 PM, with Q&A to follow; in a 1st floor conference room at the American Center for Physics, 1 Physics Ellipse, College Park, MD-- off River Rd., between Kenilworth Ave. and Paint Branch Parkway.
Abstract: The motions of nucleons within atomic nuclei lead to many different states having specific energies, angular momenta and half-lives, according to the same principles of quantum mechanics that govern electron orbitals surrounding the nuclei. Among the many nuclear excited states, some may possess half-lives sufficiently long to be directly measured by a decay curve: these states are called nuclear isomers. At the present experimental state-of-the-art, the lower limit for isomers is several nanoseconds. However, perhaps the most interesting isomers are those at the other extreme.
Truly metastable isomers exist with half-lives of seconds, days, decades and millennia. The longest-lived metastable isomer is 180mTa, with a half-life greater than the age of the universe. Since the 180Ta ground state has a half-life of only about 8.2 hours, any 180Ta found on Earth (0.012% of natural tantalum) is in the metastable excited state. The existence of nuclear isomers has provided important clues in the development of nuclear models and in understanding the synthesis of heavy elements in stars. Their long half-lives, decay modes and large energy densities have led to current practical uses (99mTc in nuclear medicine) and suggestions of potential future applications (as in isotope batteries). This presentation will give an introduction to the physics of nuclear isomers and a survey of some recent research, including searches for new metastable isomers.
Short bio: James J. (Jeff) Carroll is a physicist with the US Army Research Laboratory (ARL), Adelphi, MD, and leads a research team within its Power and Energy Division. He has published nearly 90 peer-reviewed journal articles related to nuclear physics and nuclear isomers, and has given plenary and invited talks around the world. Prior to coming to ARL in January 2011, he was a Professor in the Department of Physics and Astronomy, Youngstown State University, where he was recognized seven times as Distinguished Professor in Teaching or Research during his fifteen years. James received his Ph. D. from the University of Texas at Dallas in 1991 for nuclear isomer studies with photon sources. He is a co-discoverer of induced depletion (de-excitation) of three of the five nuclear isomers for which this process has been experimentally demonstrated.