Unique chromium beam experiment unlocks cosmic ray origins and galactic chemistry
A research team led by UMBC physicist Priyarshini Ghosh used the Facility for Rare Isotope Beams (FRIB) at Michigan State University to measure proton spallation cross sections for chromium-52. According to Ghosh, this first-of-its-kind data helps scientists translate cosmic ray observations into a precise map of the Milky Way’s chemical composition.
How does chromium-52 reveal the history of the Milky Way?
When stars die, they blast elemental nuclei into space as cosmic rays. These particles travel near light speed until they hit hydrogen atoms in the galaxy. This collision, known as “proton spallation,” breaks the nuclei into lighter elements. For instance, iron from a supernova can fragment into sodium.
According to Priyarshini Ghosh, a nuclear physicist with the UMBC Center for Space Sciences and Technology, chromium-52 is a critical piece of this puzzle. It has never been measured before, leaving a gap in how scientists trace detected elements back to their original stellar sources. By recreating these collisions in a lab, researchers can finally determine the galaxy’s true chemical history.
Why was the FRIB experiment necessary to get this data?
Collecting this specific nuclear data is expensive and labor-intensive. Ghosh noted that a sample of enriched chromium-52 the size of a chocolate square costs roughly $150,000. To avoid this cost, the team used a different method at FRIB.
The researchers produced chromium-52 by triggering nuclear reactions between a nickel-58 beam and a carbon target. The experiment ran for 43 hours, using a liquid hydrogen target to mimic the environment of space. Jorge Pereira, FRIB magnetic spectrometer operation group leader, stated that FRIB allows scientists to reproduce the specific process of cosmic rays traveling from a dying star under controlled conditions.
The three-step process used at FRIB:
- Creation: The particle accelerator and separator created a chromium-52 beam similar to cosmic rays.
- Simulation: A liquid hydrogen target simulated the hydrogen encountered in space.
- Measurement: The S800 spectrometer recorded what happened to the rays during the collision.
What happens next for cosmic ray missions like SuperTIGER?
The results from this experiment will directly support high-profile missions, including ACE-CRIS and SuperTIGER. Without precise “cross section” data, scientists can’t be certain if a detected element was created in a star or if it’s a fragment of a heavier element that broke apart during its journey.
This work is part of a broader strategic shift at NASA Goddard Space Flight Center and UMBC. The focus is moving toward proton-based cross sections to build a foundational database. According to the research team, this database won’t just map the galaxy; it could eventually help scientists analyze the chemical composition of planetary surfaces.
Frequently Asked Questions
What is proton spallation?
It’s a process where high-energy cosmic ray nuclei collide with hydrogen atoms (protons), causing the nuclei to fragment into lighter elements.
Why is chromium-52 important?
Chromium-52 provides specific insights into galactic processes, but because it had never been measured in a lab, it created uncertainty in astrophysical models.
How long does it take to analyze this data?
According to Priyarshini Ghosh, the data analysis phase takes nearly a year following the actual beam runs.
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