Researchers at the Facility for Rare Isotope Beams (FRIB) have successfully recreated a rare cosmic reaction in a laboratory setting, providing a new way to track the origin of some of the universe's rarest elements.
Using a rare isotope beam, the team directly measured the process by which arsenic-73 captures a proton to form selenium-74. The experiment offers new data on the formation of p-nuclei, which are proton-rich isotopes heavier than iron that have puzzled astrophysicists for decades.
Published in Physical Review Letters, the study involved a collaboration of more than 45 scientists from 20 institutions across the United States, Canada, and Europe.
Solving the p-nuclei mystery
Most elements heavier than iron form through neutron-capture processes in stars. However, p-nuclei cannot be produced this way, leaving their origin a subject of intense study for over 60 years.
One leading theory suggests these elements are created via the gamma process during supernova explosions. In these extreme environments, intense heat produces gamma rays that strip particles from existing heavy nuclei.
Because many isotopes involved in this process are short-lived, scientists have historically relied on theoretical models rather than direct measurements.
"Even though the origin of the p-nuclei has been a topic of study for over 60 years, measurements of important reactions on short-lived isotopes are almost non-existent," said Artemis Tsantiri, a postdoctoral fellow at the University of Regina who led the study.
Tsantiri noted that experiments of this scale are only now possible with advanced facilities like FRIB.
To conduct the test, the team generated a beam of arsenic-73 using FRIB's ReA accelerator and directed it into a chamber of hydrogen gas. By measuring the forward reaction, the researchers could determine the speed of the reverse process, which is critical to understanding how selenium-74 is created and destroyed in space.
While the new measurements helped cut uncertainty in astrophysical models by half, the data also revealed gaps in current theories. The findings suggest that while the team has clarified the limits of how the lightest p-nucleus is formed, the complete story of stellar nucleosynthesis is not yet understood.