Reverse-Engineering the Neutron-Nucleus Interaction

Project Overview

In high neutron fluence environments, for example neutron star mergers, neutrons are frequently absorbed by the variety of nuclei present in the bulk material, quickly producing unstable, neutron rich isotopes. The delicate interplay of neutron capture with other reaction and decay channels, such as beta-decay, neutron elastic and inelastic scattering, multiple neutron emission, defines the complex reaction network which will give rise to the final isotopic abundance observed in the material. The accuracy of the simulations used to predict the outcomes of such processes rely heavily on the quality of the theoretical models implemented, of which the neutron-nucleus interaction (also known as the optical model potential, OMP) is a critical ingredient. In this project, a new nuclear reaction-theory formalism, combined with state-of-the-art structure calculations, was developed and demonstrated to determine the effective OMP from experiments at both stable and radioactive-beam facilities. Making use of an innovative approach, the critical lack of model constraints was overcome by utilizing experimental (d,p) reactions (a process in which a deuteron drops a neutron in the nucleus under study) data in a new way. Our project developed the code selfe , and used this code to calculate the OMP associated with the medium-mass nucleus 24Mg (both for protons and neutrons) and with the exotic light nucleus 8He. This will allow us to calculate the 8He(d,p) reaction cross section within the Green's Function Transfer (GFT) formalism, and propose a high-profile experiment at the Facility for Rare Isotope Beams (FRIB) to shed light on the controversial nature of the beyond-the-drip line nucleus 9He.  

Mission Impact

The project will positively impact the Nuclear, Chemical and Isotopic Science Core Competency, and, more specifically, the Structure and Reactions of Nuclei R&D priority by taking an important step towards the long standing goal of having a predictive theory for OMPs across the nuclear chart. We will build upon LLNL's nuclear data and theory expertise in the integration of structure and reaction theory, and enrich current theoretical efforts, such as the (d,pγ) surrogate program. It will strengthen the leadership position of LLNL in fully exploiting the capabilities of the DOE's Facility for Rare Isotope Beams (FRIB), and obtain DOE funding for experimental proposals, including (d,p) experiments on short-lived fission yields. It will also benefit Nuclear Weapons Science by providing the microscopic description and prediction of neutron capture rates and reaction networks important for stockpile stewardship and nuclear forensics. The new capability for providing Optical Model Potential (OMP) with UQ will strongly align with the current LLNL efforts concerning nuclear data evaluation, specially regarding the future planned activity in developing mid-fi and low-fi evaluations, and will be integrated in programatically funded projects.

Publications, Presentations, and Patents

D. Bazin, D. et al., 25 (2023)."Perspectives on Few-Body Cluster Structures in Exotic Nuclei." Few-Body Systems 64. DOI: 10.1007/s00601-023-01794-0. Report number: JLAB-THY-23-3921.

Hebborn, C., F. M. Nunes, G. Potel, W. H. Dickhoff, J. W. Holt, M. C. Atkinson, R. B. Baker et al. "Optical potentials for the rare-isotope beam era." Journal of Physics G: Nuclear and Particle Physics 50, no. 6 (2023): 060501. United Kingdom. https://doi.org/10.1088/1361-6471/acc348.

Weinert, M. et al. 6 December 2021. "Microscopic Structure of the Low-Energy Electric Dipole Response of 120 SN." Phys Rev. Lett. 127 (2021) 242501. doi: https://doi.org/10.1103/PhysRevLett.127.242501

Gregory Potel Aguilar, "Probing the 11Li low-lying dipole strength via 9Li(t,p)" (Presentation, COMEX 7th, Catania, Italy, 11-16 June 2023.)

Gregory Potel Aguilar, Nuclear Josephson effect" (Presentation, IVth Topical Workshop on Modern Aspects of Nuclear Structure, Bornio, Italy, February 2023).

Gregory Potel Aguilar, "Nuclear Josephson effect" (Presentation, 28th International Nuclear Physics Conference INPC 2022, Cape Town, South Africa, September 2022).

Gregory Potel Aguilar,"Ab Initio calculations of nuclear reactions and clustering" (Presentation, FRIB-TA Topical Program, East Lansing, MI, USA, August 2022).

Gregory Potel Aguilar, et al.,"Optical Potentials in Nuclear Physics" (Presentation, FRIB-TA Topical Program, East Lansing, MI, March 21 - April 1, 2022).