Connecting Nuclear Structure to Stellar Astrophysics: Neutron Skin in Tin Isotopes

Jack Silano | 19-LW-004

Project Overview

The first observation of a neutron star merger by the LIGO-Virgo scientific collaboration in 2017 highlights the need to improve our fundamental understanding of the equation of state (EOS) of dense, neutron rich matter. The origin of heavy elements in the rapid neutron-capture process (r-process) and the structure of neutron stars are governed by the properties of neutron rich matter, for which experimental data is limited. Further analysis of this historic event and all future neutron star mergers relies on constraining the nuclear equation of state with experimental observables.

We proposed a novel method for systematically studying the evolution of the neutron skin in stable tin isotopes by measuring the low-energy nuclear dipole strength over the broadest possible range of neutron-to-proton ratios in a single element. Nuclear resonance fluorescence with 100 percent linearly polarized photons from the High Intensity Gamma-ray Source facility was used to selectively measure the electric dipole (E1) photoabsorption strength of tin-112 and tin-124 at excitation energies from 3.5 megaelectron volt (MeV) up to neutron separation, where the Pygmy Dipole Resonance dominates. The dipole polarizabilities of tin-112 and tin-124 were measured to be 7.14 ± 0.21 fm3 and 7.90 ± 0.24 fm3, respectively. These uniquely, systematically consistent measurements provide highly accurate experimental data for improving microscopic nuclear models, as well as calculations of astrophysical nucleosynthesis and neutron star structure.

Mission Impact

The project addressed a fundamental quantity describing nuclear matter at extreme conditions. We provided high-precision and highly sensitive data to constrain the EOS properties that are of paramount importance for low-energy nuclear physics, as well as nuclear astrophysics applications. We addressed important nuclear data needs for constraining the capture cross-section on unstable isotopes by developing a new experimental capability for precision gamma-ray decay measurements. In addition, this effort aligns with Laboratory core competencies of nuclear, chemical, and isotopic science and technology, and high-energy-density science.

Publications, Presentations, and Patents

Silano, J. A. et al. 2019a. "Connecting Nuclear Structure to Stellar Astrophysics: Neutron Skin in Tin Isotopes." American Physical Society April Meeting, Denver, CO, April 2019. LLNL-PRES-771264

——— 2019b. "Connecting Nuclear Structure to Stellar Astrophysics: Neutron Skin in Tin Isotopes." 2019 Fall Meeting of the American Physical Society Division of Nuclear Physics, Crystal City, VA, October 2019. LLNL-PRES-793057