U.S. Army Research Laboratory (ARL) physicist Dr. Jeff Carroll of the Sensors and Electron Devices Directorate's (SEDD's) Power and Energy Division was recently recognized with a publication in Physical Review Letters.

International in scope, Physical Review Letters is the premier peer-reviewed journal for basic physics research, including articles of sufficient quality and value to be disseminated to all physicists regardless of their field.

Per the Web of Science, this is only the fourth time, and the first since 2006, that a publication affiliated with ARL has appeared in Physical Review Letters.

The publication, titled "Direct Observation of Long-Lived Isomers in 212Bi," describes results from an international collaboration that included Carroll, who helped arrange the "beamtime," perform the experiment, interpret the results and prepare the manuscript.

"International collaborations of this type, in this case led by physicists at the University of Surrey, require national-scale research facilities, with unique ion accelerators and detector systems," said Carroll.

In order to utilize these facilities, members of collaborations propose a specific study, competing for research time at the facility.

If approved, the study is scheduled for a typical 5 to 7-day period with the experiment running 24-hours per day, requiring scientists to assemble and perform shifts to insure data collection and make modifications to the experimental conditions on the fly.

In addition, the use of such facilities is generally free of cost to participating researchers.
At the particular facility where this collaborative experiment took place, the German GSI Institute for Heavy Ion Research, it can often take years for an experiment to be approved and scheduled, so beamtime is a precious commodity.

The experiment Carroll conducted with fellow scientists, which incorporated insights from his research as a professor at Youngstown State University in Ohio, resolved a long-standing discrepancy between the measured and calculated lifetime for a specific nuclear isomer in 212Bi.

It took about six months of submission for the experiment to be accepted by GSI, and a total of about four years before beamtime was actually scheduled.

According to Carroll, nuclear isomers are long-lived excited states of atomic nuclei with lifetimes ranging from microseconds to many millennia.

Many of the longer-lived isomers are of great interest to ARL, as they store about 100,000 times the energy per unit mass of chemicals.

Since isotopes possessing such long-lived states often have shorter-lived, unstable ground states, some radioisotopes can be "switched" from energy-storing to energy-releasing forms upon demand.

"Although high-risk, nuclear isomers have the potential to enable new types of batteries for applications like persistent, low-power sensors, and this is being investigated under a basic research program within the Power Components Branch, Energy and Power Division of SEDD," noted Carroll.

A lingering problem has been the inability to accurately predict the lifetime of isomers using modern theoretical approaches, so measurements were always required.

Now, the published work shows that calculations may be more accurate in some instances than previously thought, and identifies the isotope 212Bi as a possible new test case for isomer "switching."

Although this research is currently basic in scope, Carroll says that the ultra-high energy densities of isomers and the ability to "switch" them to higher-power levels may lead to innovations that will benefit the warfighter.

To access the paper, visit http://prl.aps.org/abstract/PRL/v110/i12/e122502.