EAST LANSING, Mich. — An international collaboration at National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University has demonstrated a new technique for studying particles traveling at one-third the speed of light.  

The result, which will be published in Physical Review Letters, opens up new doors to investigating rare isotopes – fleeting versions of elements not normally found on Earth.

“It’s opening up a whole range of possible studies,” said Roderick Clark, a physicist and co-leader of the nuclear structure group at Lawrence Berkeley National Laboratory, who was not involved in the experiment. “That’s as far as you can go, the frontiers of this research. This is one of the areas that NSCL is leading the world in.”

In the study, NSCL users from the Institute for Nuclear Physics of the University of Cologne in Germany and Central Michigan University teamed with NSCL researchers for a first-ever measurement of the rare isotope germanium-64, Ge-64. Specifically, the researchers gauged the amount of time it takes for an excited, high-energy version of the isotope to decay into a lower energy state – information crucial to nuclear scientists seeking to characterize shape and structure of rare isotopes.

“To make this experiment happen, you need to bring together all the top elements you have available in the lab and from our users,” said Krzysztof Starosta, NSCL assistant professor and the paper’s lead author. “You need everything to be optimized, and it happened for this particular experiment.”

All nuclei are made up of protons and neutrons, and the stable form of Ge-73, relatively abundant on Earth and commonly used as a semiconductor in the computing industry, has 32 protons and 41 neutrons. Ge-64, in contrast, has an equivalent number of protons and neutrons – 32 of each – an exceedingly rare combination for this element.

Physicists are interested in isotopes like Ge-64 with mirror-image sets of protons and neutrons that fall within a specific mass region – heavier than nickel and lighter than tin. It is a nuclear neighborhood marked by strange phenomena, including nuclei that rapidly change from being round to cigar- or pancake-shaped. The broad theoretical outlines of shape-shifting behavior are well understood, yet until now, precise experimental observation has been difficult to achieve, according to the researchers.

NSCL studies isotopes by fragmenting beams of nuclei traveling at more than 62,000 miles per second. This fast-beam method holds certain advantages over alternative means of producing rare isotopes, allowing physicists to study nuclei at the extreme edge of existence.

But studying such speeding nuclei is rife with challenges, too, such as filtering and purifying the beam and having the right equipment to detect the few sought-after isotopes from the many billions of billions of other particles in the beam.

“Until now, such challenges had hindered the success of lifetime measurement experiments at fast-beam facilities,” said Starosta.

The experimental result is only the second time a precise lifetime measurement has been made in the mysterious portion of the nuclear landscape where unusual proton-neutron ratios may cause strange behavior.

The research was supported by the U.S. National Science Foundation and the Gesellschaft für Schwerionenforschung in Germany.

NSCL is a world-leading laboratory for rare isotope research and nuclear science education.

A preprint version of the paper is available at http://lanl.arxiv.org/abs/nucl-ex/0703021.

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