Where in the universe are the heavy elements on the periodic table created?

New constraints on theoretical nuclear models will help to determine the astrophysical site of the rapid neutron capture process

One of the longstanding open problems in physics is the quest to understand how the elements on the periodic table are created in nature. The heaviest of these elements, those above iron, are believed to be forged in cataclysmic astrophysical events such as supernova or the merging of compact objects, for instance, neutron stars. In the rapid neutron capture or r-process of nucleosynthesis, neutrons are absorbed by light nuclei at astonishing rates to create heavy nuclei. However, we do not yet know under exactly what conditions this process takes place in the universe.

One way to resolve the question of the site of the r-process is to compare the results of computer simulations of proposed astrophysical environments to the pattern of r-process abundances observed in the solar system. This approach requires the answer to many other questions and interweaves knowledge of both astrophysical events and nuclear structure. For example, one source of uncertainty in the abundance yields predicted by simulation is the adopted nuclear physics model. The nuclear models have large uncertainties since the nuclei that participate in the r-process are so neutron-rich they are tremendously difficult to produce in the laboratory. This lack of experimental information prevents scientists from using pattern comparisons to pinpoint the astrophysical event responsible for the r-process.

Researchers led by M. Mumpower at Los Alamos National Lab have developed a transformative approach to this problem. They have constructed a new technique to glean information about the r-process site from anticipated advances in nuclear physics. They use observations of r-process abundances in the solar system to place an additional constraint on the nuclear models. This approach allows the researchers to reverse engineer nuclear properties from well-defined astrophysical observations producing new nuclear model predictions. The researchers have found that each different type of r-process conditions produces a distinct signature in the updated nuclear model prediction, thus allowing an avenue for the site of the r-process to be tested in the laboratory.

Figure: Final r-process abundances before (dashed) and after (shaded) the application of the reverse engineering framework compared to solar data (black dots) for three astrophysical trajectories. The match to solar data yields new predictions for nuclear properties of neutron-rich nuclei.


The feasibility of this new frontier is closer than you might think, as new facilities are being constructed which utilize radioactive beams capable of producing some of the nuclei that participate in the r-process. Coupling these exciting new results with experimental campaigns will allow researchers to fine tune their measurements to look for the predicted theoretical signatures in the nuclear models. This combined theoretical and experimental effort will help to answer one of the most difficult open problems in all of physics: where in the universe are the heavy elements on the periodic table created?

About the Authors

Matthew R. Mumpower is a postdoctoral researcher in the Theoretical Division of Los Alamos National Lab. His research interests focuses on nuclear models and fission which have a wide range of applications including astrophysical environments such as the r-process. More information is available on his website.


Gail C. McLaughlin is a professor in the Department of Physics at North Carolina State University. Her research interests are in neutrino and nuclear astrophysics, with a particular focus on merging compact objects and core collapse supernovae.


Rebecca Surman is an Associate Professor in the Department of Physics at the University of Notre Dame. Her research targets the origins of the heaviest elements and neutrino and nuclear physics aspects of element synthesis in extreme astrophsyical environments.


Andrew W. Steiner is a joint faculty assistant professor at the University of Tennessee in Knoxville and Oak Ridge National Laboratory. He is an expert in the aspects of neutron star structure and evolution that involve nuclear physics.

Reverse engineering nuclear properties from rare earth abundance in the r process

M R Mumpower, G C McLaughlin, R Surman and A W Steiner, J. Phys. G: Nucl. Part. Phys 44 034003

belongs to the special issue: Emerging Leaders, which features invited work from the best early-career researchers working within the scope of J. Phys. G. This project is part of the Journal of Physics series’ 50th anniversary celebrations in 2017. Matthew R. Mumpower was selected by the Editorial Board of J. Phys. G as an Emerging Leader.

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Categories: Journal of Physics G: Nuclear and Particle Physics, JPhys+

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