How Rapid is the Rapid Neutron Capture Process?

Project Overview

The rapid neutron capture ‘r-process' is responsible for producing about half of the heavy elements in nature and is thought to occur in extreme, high neutron density and high temperature environment in the cosmos such as binary neutron star mergers. The 'neutron-rich' isotopes relevant to neutron capture in the r-process are so short lived that their associated reaction rates cannot be conventionally measured in the laboratory. Intriguing recent results for neutron-rich strontium isotopes suggest that the probability of neutron capture for nuclei this far from stability may be a factor of ten higher than our present understanding. To confirm or refute these results we are determining the neutron capture reaction rate for radioactive strontium-93 using the surrogate nuclear reaction approach. We fielded a measurement at TRIUMF laboratory, using a radioactive beam of strontium-93 and the TIGRESS/SHARC spectrometer to measure deuteron-proton charged particle reactions in coincidence with gamma rays. The analysis the resultant data and associated theory interpretation are nearing completion to answer this important question on neutron capture rates far from nuclear stability relevant to nucleosynthesis processes like the r-process.

Mission Impact

This high-profile project facilitated a new collaboration with scientists at TRIUMF laboratory and paved the way for future radioactive beam experiments there. Furthermore, the science and technical developments achieved will strengthen future experiment proposals at FRIB and other US facilities for basic and applied science. The surrogate nuclear reaction approach can directly impact national security missions and will support the NNSA goal to advance the science, technology, and engineering competencies that are the foundation of those missions. This research advances Core Competencies in Nuclear, Chemical, and Isotopic Science and Technology and High Energy Density Science.

Publications, Presentations, and Patents

A. L. Richard, "Indirect Neutron-Capture Constraints for the Astrophysical i-Process" (Presentation, IReNA Online Seminar Series, virtual, Sept. 15, 2023). 

A. L. Richard, "Impact of the experimentally constrained 93Sr(n,g)94Sr reaction for the astrophysical i-process" (Presentation, 2023 CeNAM Frontiers in Nuclear Astrophysics Meeting, East Lansing, MI, May 22-26, 2023). 

A. L. Richard, "Indirect Neutron-Capture Techniques for the i-Process" (Presentation, i-Process Nucleosynthesis Workshop and School, May 16, 2023).

A. L. Richard, "Impact of the experimentally constrained 102,103Mo(n,g) reaction rates on the Mo, Ru, and Rh abundances predicted for the i-process" (Presentation, i-Process Nucleosynthesis Workshop and School, Limassol, Cyprus, May 15-19, 2023).

A. L. Richard, "Experimental Constraints on Statistical Quantities for Nuclear Astrophysics" (Presentation, Workshop for Applied Nuclear Data Activities - WANDA, February 2023).

A. L. Richard, "Particle-Gamma Coincidence Studies of 93Sr(d,p)94Sr via the Surrogate Reaction Method" (Presentation, 2022 Fall Meeting of the APS Division of Nuclear Physics, New Orleans, LA, October 27-30, 2022).

A. L. Richard, "Particle-Gamma Coincidence Studies of 93Sr(d,p)94Sr via the Surrogate Reaction Method" (Presentation, Nuclear Structure 2022, Berkeley, CA, June 13-17, 2022).

A. L. Richard, "Experimentally Constrained 102,103Mo(n,gamma) Reaction Rates and Their Impact on Predicted i-process Abundances" (Presentation, JINA-CEE Frontiers Meeting, Notre Dame, South Bend, IN,  May 23-27, 2022).