GoKawiilGold cannot form until certain unstable atomic nuclei break apart. Exactly how those nuclear transformations unfold has long been difficult to determine. Now, nuclear physicists at the University of Tennessee (UT) report three discoveries in a single study that clarify important parts of this process. Their findings could help researchers build improved models of the stellar events that create heavy elements and better predict the behavior of exotic atomic nuclei.
Heavy elements such as gold and platinum are forged under extraordinary conditions, including when stars collapse, explode, or collide. These events trigger the rapid neutron capture process (or r-process for short). During this process, an atomic nucleus absorbs neutrons in rapid succession. As the nucleus grows heavier and more unstable, it eventually breaks down into lighter and more stable forms.
Along this pathway across the nuclide chart, a common sequence involves beta decay of the parent nucleus followed by the release of two neutrons. The atomic nuclei involved in these reactions are extremely rare and unstable, making them difficult or even impossible to study directly in experiments. Because of this, scientists rely heavily on theoretical models, which must be tested and refined using laboratory data.
Studying Rare Nuclei With CERN's ISOLDE Facility
To investigate the process more closely, UT researchers collaborated with scientists from several institutions. The team included UT Graduate Students Peter Dyszel and Jacob Gouge, Professor Robert Grzywacz, Associate Professor Miguel Madurga, and Research Associate Monika Piersa-Silkowska. Their work also built on data analysis methods developed by Research Assistant Professor Zhengyu Xu.
The researchers began with large quantities of the rare isotope indium-134.
"These nuclei are hard to make and require a lot of new technology to synthesize in sufficient quantities," Grzywacz explained.
The team carried out the experiments at the ISOLDE Decay Station at CERN, which produced abundant indium-134 nuclei and used advanced laser separation techniques to ensure their purity. When indium-134 undergoes decay, it generates excited forms of tin-134, tin-133, and tin-132.
Using a neutron detector funded through the National Science Foundation Major Research Instrumentation program and constructed at UT, the scientists uncovered three major findings. The most significant result was the first measurement of neutron energies associated with beta-delayed two-neutron emission.
"The two-neutron emission is the biggest deal," Grzywacz said.
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