This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The Compact Accelerator System for Performing Astrophysical Research (CASPAR) recreates conditions inside stars to study how elements are made. The experiment recently restarted with a new target—the ninth element on the periodic table, fluorine.
"What I find most interesting about fluorine is that we think the reaction that created this element took place inside stars pretty early on in the universe," said Leah Zimmer, a Ph.D. candidate in physics at the University of Notre Dame who is using CASPAR to study how fluorine is formed in early stars. "We're really interested in studying interactions with fluorine, as it can be a piece of the puzzle as to how the first stars were formed way back in the early universe." Elements are forged by the intense heat and pressure inside stars that smash together protons and neutrons in fusion reactions. Elements with the smallest atomic numbers, like hydrogen and helium, form the first building blocks in the sequence.
As more protons and neutrons are added inside the cosmic cauldrons, the atomic numbers increase to form heavier elements. CASPAR can mimic these stellar reactions. The small particle accelerator is located nearly a mile underground at Sanford Underground Research Facility (SURF).
It can smash protons into specialized targets to recreate the kinds of conditions that form elements like fluorine. "CASPAR helps us better understand the stellar environment: what elements are produced, how they are produced, what energy they produce while forming and the conditions we can recreate to give us information about the insides of stars," said Dan Robertson, the principal investigator on CASPAR and a research professor in the Department of Physics & Astronomy at the University of Notre Dame. Fluorine, it turns out, is a key building block in the process.
Once in a while, an interaction with fluorine will help elemental production escape a cycle of elements that some stars get stuck in. In these cases, carbon, nitrogen and oxygen are repeatedly produced and then destroyed. This process, called the CNO cycle, can stop the formation of heavier elements.
"But fluorine is one of these breakout reactions that, in certain conditions, can jump from carbon, nitrogen, oxygen, bam, straight through fluorine and on to the heavier elements," Robertson said. Even with a working particle accelerator sitting in an underground lab, recreating the environment where fluorine is formed is much easier said than done. As part of her Ph.D. research, Zimmer had to make the fluorine-based target for the accelerator to hit.
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