Unique chromium beam experiment unlocks cosmic ray origins and galactic chemistry
image: The research team, led by UMBC's Priyarshini Ghosh, ran a novel experiment on the S800 Spectrograph at the Facility for Rare Ion Beams at Michigan State University. They expect the results to increase understanding of the chemical makeup of the Milky Way galaxy.
Credit: Facility for Rare Isotope Beams/Michigan State University
When a star dies, it generates an explosion of elemental nuclei and hurls them into space. Those elements, called cosmic rays, travel at nearly the speed of light, and eventually, some of them encounter manmade detectors. Recording how many of each of these elements shows up helps scientists better understand cosmic processes—but despite incredible research advances over the last century, uncertainty around how these elements transform as they travel across the light years has left fundamental questions about our galaxy's composition unanswered.
Priyarshini Ghosh, a UMBC nuclear physicist with the Center for Space Sciences and Technology, is at the forefront of research that could significantly improve our understanding of these cosmic phenomena.
Ghosh and her collaborators have just completed a pioneering experiment at the Facility for Rare Isotope Beams (FRIB) at Michigan State University, where they generated and then fragmented a beam of chromium-52 nuclei. Chromium-52 is of particular interest because it can shed light on different processes happening in our galaxy, and yet it has never been measured.
As cosmic ray nuclei like chromium-52 race through the galaxy, they can collide with hydrogen atoms and fragment into lighter elements through a process called “proton spallation.” For example, iron forged in a supernova might break apart into sodium and other particles. The experiment, which occurred earlier this month, measured these exact interactions—recording “proton spallation cross sections” for chromium-52—to help scientists confidently trace detected elements back to their origins. By recreating these high-energy collisions in a laboratory, researchers aim to resolve longstanding discrepancies and reveal the galaxy’s true chemical history.
“The experiment was not only successful in producing the isotopes we need to understand these galactic mechanisms,” Ghosh says, “but the beam runs also provided data that can give us insights into the intricate nuclear processes of proton spallation.”
This kind of nuclear data provided by this experiment is hard to come by, because the experiments required to collect it are costly and labor- and time-intensive. But more data is needed, Ghosh says, because “nuclear data acts as a translator from the data collected by the missions like Voyager 1 and 2, converting it into a meaningful understanding of our galaxy.”
Closing the gap
"What makes this experiment particularly challenging is that enriched chromium-52 costs approximately $150,000 for a sample the size of a chocolate square," Ghosh notes. To overcome this, FRIB will produce chromium-52 from nuclear reactions between a beam composed of nickel-58 and a carbon target.
The experiment ran for 43 hours, during which the team successfully collected data on 50 – 60 isotopes of interest resulting from element collisions and fragmentation. Now, data analysis will take nearly a year, with results expected to improve the precision of astrophysical models and our understanding of our galaxy. That analysis “is another adventurous endeavor,” Ghosh says.
“One of the most exciting aspects of this project is that FRIB offers unique opportunities to reproduce (under control) a very specific process occurring in the universe: the traveling of cosmic rays emitted by a dying star through the galaxy,” said Jorge Pereira, FRIB magnetic spectrometer operation group leader.
The experiment had three key steps. First, “the particle accelerator and separator at FRIB created a nuclear beam of chromium-52 with characteristics similar to cosmic rays. Second, a liquid hydrogen target mimicked the hydrogen that these cosmic rays encounter as they fly through space. Third, the S800 spectrometer will allow us to infer what happens to those cosmic rays as they travel.”
Decoding galactic evolution
Ghosh and her colleagues’ work is part of a developing program at NASA Goddard Space Flight Center and UMBC focused on proton-based cross sections, whose study has been limited. The upcoming experiment represents a strategic shift toward recognizing that proton spallation reactions are essential to interpreting data from space missions and understanding galactic chemical evolution.
This kind of experiment can even help analyze the composition of the surface of planets. The UMBC-led collaboration aims to build a foundational database that could transform our ability to translate cosmic observations into accurate models of how elements are created and distributed throughout the galaxy.
The experiment's results will also directly support missions like ACE-CRIS and SuperTIGER. Ghosh's nuclear data will enable scientists to interpret the observations accurately.
For Ghosh, the excitement lies in the experimental challenge itself. "This is such a feat of nuclear engineering," she reflects. "We're using detectors to expose the physics in specific ways—arm-wrestling with nature to get the answers we need."