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National Superconducting
Cyclotron Laboratory

Betty Tsang
Betty Tsang
Professor
Nuclear Chemistry
PhD, Chemistry, University of Washington, 1980
Joined NSCL in December 1980
Phone 517-908-7386
Office 1018
tsang at nscl.msu.edu

Betty Tsang

Professional Homepage

As an experimentalist, I study collisions of nuclei at energies at approximately half the speed of light. From the collisions of nuclei, 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. The shaded blue region in the picture shows the pressure-density relationship, also known as equation of state (EoS), of pure neutron matter deduced from GW170817 observation. The two contours on the figure are two “extreme” formulations of symmetry pressure, which contribute significantly to the core of a neutron star added to the pressure from the heavy-ion collision data for nuclear matter that has the same number of neutrons and protons obtained from experiments. 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 the nucleus you encounter everyday, 2.3x1014 kg/cm3) experiments are planned at NSCL, 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) emitted from nucleus-nucleus collisions. We studied the collisions using 132Sn (heavy radioactive tin isotope) and 108Sn (light radioactive tin isotopes) in 124Sn and 112Sn, heaviest and lightest stable tin targets. The pions detected in this experiment allow us to extract the symmetry pressure at twice of the nuclear matter density.

In a series of experiments at NSCL, 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 the High Performance Computer Center at MSU in our quest to understand the role of symmetry energy in nuclear collisions, nuclear structure and neutron stars. Our recent series of experiments using Ca isotope beams on tin and nickel isotope targets would allow us to place constraints on various input parameters used to mimic the physics of the nuclear interactions in these transport models. We aim to have better symmetry energy constraints that have smaller errors than the current astronomical ones.

Selected Publications

Symmetry Energy Constraints from GW170817 and Laboratory Experiments, M.B. Tsang, P. Danielewicz, W.G. Lynch, and C.Y. Tsang, Phys. Lett. B 795, 533 (2019)

Insights on Skyrme parameters from GW170817, C.Y. Tsang, M.B. Tsang, P. Danielewicz, W.G. Lynch, F.J. Fattoyev, Phys. Lett. B 796, 10 (2019)

Constraints on the symmetry energy and neutron skins from experiments and theory, M.B. Tsang et al., Phys. Rev. C 86, 015803 (2012)

Constraints on the Density Dependence of the Symmetry Energy, M.B. Tsang, Y. Zhang, P. Danielewicz, M. Famiano, Z. Li, W.G. Lynch,
A.W. Steiner, Phys. Rev. Lett. 102, 122701 (2009)