New Measurement Of Stellar Neutron Source Reaction Fixes Long-Standing Discrepancies
The Jinping Underground Nuclear Astrophysics (JUNA) collaboration has reported a recent direct measurement of the cross-section of an essential stellar neutron source reaction, 13C(α, n)16O. The study research was published in Physical Review Letters on September 23.
By reaching the most accurate cross-sectional measurement of this reaction at astrophysical energies so far, the study research has fixed long-standing discrepancies among previous data on this reaction, which is fundamental for understanding the origin and abundance of elements heavier than iron in the universe.
The origin of said elements is one of eleven Physics Questions for the 21st Century, and neutrons are the key to changing iron into heavier elements. The rate of the neutron source reaction determines how many of these heavier elements could be made in stars.
The neutron source reaction
The 13C(α, n)16O reaction, first proposed in theory as the primary neutron source in stars by Cameron and also Greenstein in 1954, offers neutrons needed in the synthesis of approximately half of all heavier-than-iron elements in the universe. It has long been an target of experimental nuclear astrophysics to accurately measure this reaction at astrophysical energies (0.15– 0.54 MeV). However, the corresponding reaction cross section is very small, which makes it extremely difficult to measure.
In the past 7 years, the JUNA collaboration has developed a series of scientific equipment installed at the China Jinping underground Laboratory (CJPL), which is currently the deepest underground laboratory in the world. The equipment includes an accelerator delivering the most intense α beam in the underground laboratories worldwide; high-power, thick targets that can survive bombardment by an intensive beam of hundreds of coulombs; and a high-sensitivity, low-background neutron detection array.
Recent developments
Using these developments and the ultra-low background environment at CJPL, the research group successfully performed a direct measurement of the cross-section of the 13C(α, n)16O reaction in the astrophysical energy range of 0.24– 0.59 MeV. The measured power range was further extended to 1.9 MeV by using the 3 MV tandem accelerator at Sichuan College.
Providing the first consistent measurement covering the energy range from the stellar energy region up to high energies, the study obtained the most accurate stellar reaction rate for the 13C(α, n)16O reaction to date.
According to Prof. Kajino, a nuclear astrophysicist from Beihang University, the current precise data of this reaction cross section offer with the firm basis to develop astronomical models of the i- and s-process nucleosyntheses to construct a new picture of Galactic chemical evolution of heavy nuclei.
Read the original article on PHYS.
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