Far out cosmology: how heavy elements might be made (Introduction)

by David Turell , Tuesday, March 31, 2020, 22:29 (1696 days ago) @ David Turell
edited by David Turell, Tuesday, March 31, 2020, 23:27

We know how very light carbon is made in stars. How about the heavy ones?

https://phys.org/news/2020-03-physicists-heavy-elements.html

"A long-held mystery in the field of nuclear physics is why the universe is composed of the specific materials we see around us. In other words, why is it made of "this" stuff and not other stuff?

"Specifically of interest are the physical processes responsible for producing heavy elements—like gold, platinum and uranium—that are thought to happen during neutron star mergers and explosive stellar events.

"Scientists from the U.S. Department of Energy's (DOE) Argonne National Laboratory led an international nuclear physics experiment conducted at CERN, the European Organization for Nuclear Research, that utilizes novel techniques developed at Argonne to study the nature and origin of heavy elements in the universe. The study may provide critical insights into the processes that work together to create the exotic nuclei, and it will inform models of stellar events and the early universe.

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"At these magic numbers, of which 8, 20, 28, 50 and 126 are canonical values, nuclei have enhanced stability, much as the noble gases do with closed electron shells. Nuclei with neutrons above the magic number of 126 are largely unexplored because they are difficult to produce. Knowledge of their behavior is crucial for understanding the rapid neutron-capture process, or r-process, that produces many of the heavy elements in the universe.

"The r-process is thought to occur in extreme stellar conditions such as neutron-star mergers or supernovae. These neutron rich environments are where nuclei can rapidly grow, capturing neutrons to produce new and heavier elements before they have chance to decay. (my bold)

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"'No other facility can make mercury beams of this mass and accelerate them to these energies," said Kay. "This, coupled with the outstanding resolving power of the ISS, allowed us to observe the spectrum of excited states in 207Hg for the first time."

"The ISS is a newly-developed magnetic spectrometer that the nuclear physicists used to detect instances of 206Hg nuclei capturing a neutron and becoming 207Hg. The spectrometer's solenoidal magnet is a recycled 4-Tesla superconducting MRI magnet from a hospital in Australia. It was moved to CERN and installed at ISOLDE, thanks to a UK-led collaboration between University of Liverpool, University of Manchester, Daresbury Laboratory and collaborators from KU Leuven in Belgium.

"Deuterium, a rare heavy isotope of hydrogen, consists of a proton and neutron. When 206Hg captures a neutron from the deuterium target, the proton recoils. The protons emitted during these reactions travel to the detector in the ISS, and their energy and position yield key information on the structure of the nucleus and how it is bound together. These properties have a significant impact on the r-process, and the results can inform important calculations in models of nuclear astrophysics.

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"The first analyses of the data from the CERN experiment confirm the theoretical predictions of current nuclear models, and the team plans to study other nuclei in the region of 207Hg using these new capabilities, giving deeper insights into the unknown regions of nuclear physics and the r-process."

Comment: very technical paper, but we are learning to answer the question as to why we have 92 natural elements from hydrogen to uranium. dhw asks the question today in another thread wondering why the universe is so big and has such weird parts. To make our elements is one new answer. He asks the question as if God didn't know what He was doing. (Tuesday, March 31, 2020, 11:05)