Betty Tsang



Education and training

  •  BS, Mathematics, California State College, 1973
  •  MS, Chemistry, University of Washington, 1978
  •  PhD, Chemistry, University of Washington, 1980


As an experimentalist, I study collisions of nuclei at energies corresponding to approximately half the speed of light. In these collisions, we can create environments that resemble the first moments of the universe after the big bang. Properties of extra-terrestrial objects such as neutron stars can be obtained from studying collisions of a variety of nuclei with different compositions of protons and neutrons. One important research area of current interest is the density dependence of the symmetry energy, which governs the stability as well as other properties of neutron stars. Symmetry energy also determines the degree of stability in nuclei.

Recent advance in gravitational wave astronomy led to the discovery of the binary neutron star merger, GW170817, in August 2017. When two neutron stars are within a few hundreds of kilometer, they exert a tidal force (similar to the force the moon exerts on the ocean of the earth) to each other. By measuring the deformation of the neutron stars due to this tidal force, one can deduce how neutron star matter reacts to pressure, temperature and density. We aim to extract information from our experiments to be so stringent that the uncertainties will be smaller than the vertical width of the contours and can thus distinguish the two forms of predicted symmetry pressure.

To explore the density region above normal nuclear matter density (which is the density of typical nuclei, 2.3x1014 kg/cm3), experiments are planned at FRIB, as well as RIKEN, Japan. Our group built a Time Projection Chamber (TPC) that was installed in the SAMURAI magnet in RIKEN, Japan. The TPC detects charged particles as well as pions (about 1/7 times the mass of proton) that are emitted from nucleus-nucleus collisions, which allow us to extract the symmetry pressure at twice of the nuclear matter density.

In a series of experiments at FRIB, we measured the isotope yields from the collisions of different tin isotopes, 112Sn+112Sn (light tin systems), 124Sn+124Sn (heavy tin systems with more neutrons) as well as the crossed reactions of 124Sn+112Sn, and 112Sn+124Sn using a state of the art high resolution detector array (HiRA) and a large area neutron wall. We measure isospin diffusions, which is related to the symmetry energy as the degree of isospin transferred in violent encounters of the projectile and target depends on the symmetry energy potentials. Through measurements and comparisons to the model simulations, we are able to obtain a constraint on the density dependence of the symmetry energy below normal nuclear matter density as shown in the blue star in the figure. This marks the density and pressure region when the crust of the neutron star with very low density starts to transition into a liquid core region composed mainly of neutrons.

In addition to experiments, we carry out transport simulations of nuclear collisions at MSU’s high-performance computing center in our quest to understand the role of symmetry energy in nuclear collisions, nuclear structure and neutron stars. We aim to achieve symmetry energy constraints that have smaller errors than the current astronomical ones.

Scientific publications