New research has unveiled a new piece of this cosmic puzzle, pointing towards the role of nuclear fission in the creation of heavy elements. The rapid neutron capture process (r-process) takes place in neutron-rich environments such as neutron star mergers and certain types of supernovae. Many chemical elements heavier than iron are thought to be produced by this process, but the details need to be better understood and cannot be studied in the laboratory.
Scientists from the Department of Energy’s Los Alamos National Laboratory examined r-process element abundances previously observed in stars. They discovered a possible fission signature, indicating that nature will most likely produce superheavy nuclei beyond the heaviest elements on the periodic table.
Recent study proves fission occurrences in the universe using observations
Previously, it was thought that fission occurs in the universe. No one, however, was able to prove it. Scientists used the most recent observations for this study. They discovered connections between light precision metals such as silver and rare earth nuclei such as europium. There is a positive relationship between increasing elements in one of these element groups and the corresponding elements in the other group.
Scientists created the fission models because the laboratory’s mission required them to measure everything relevant to weapons research. When measurements are scarce, the models aid physicists in the interpretation of experiments and the completion of data sets. The models outperform measured data by a wide margin, supporting their extrapolations without measurements. Nuclear inputs of both short-lived and long-lived species are required for studies of heavy element synthesis.
“The only plausible way this can arise among different stars,” said Matthew Mumpower, a theoretical physicist at Los Alamos National Laboratory, “is if there is a consistent process operating during the formation of the heavy elements.”
Scientists considered every possibility. They discovered that fission was the only explanation capable of reproducing the trend.
“This is incredibly profound and is the first evidence of fission operating in the cosmos, confirming a theory we proposed several years ago. As we’ve acquired more observations, the cosmos says, “Hey, there’s a signature here, and it can only come from fission.“
Study predicts heavy elements with atomic masses of 260, influencing stars
The research also suggests the possibility of heavy elements with atomic masses of 260.
Mumpower first predicted the fission fragment distributions for r-process nuclei in a 2020 study. A later investigation at TRIUMF under the supervision of collaborator Nicole Vassh was expected to produce light precision metals and rare earth nuclei.
One way to evaluate this elemental co-production is to compare the forecast to elemental abundances in a sample of stars. Ruthenium, rhodium, palladium, and silver are among these elements, as are europium, gadolinium, dysprosium, and holmium.
After searching 42 stars’ observational data, a new study discovered the expected association. The pattern, when combined with a similar pattern of elements that are slightly heavier and higher on the periodic table, identifies the fission that produced these elements.
Mumpower said, “The correlation is very robust in r-process enhanced stars with sufficient data. Every time nature produces an atom of silver, it produces heavier rare earth nuclei in proportion. The composition of these element groups is in lockstep. We have shown that only one mechanism can be responsible — fission — and people have been racking brains about this since the 1950s.”
