NSCL Directory Profile

Bill Lynch Professor Experimental Nuclear Physics   PhD, Nuclear Physics, University of Washington 1980 Joined NSCL in December 1980 Phone (517) 333-6319 Fax (517) 353-5967 Office W106   lynch at nsclmsuedu

Our research is focused upon understanding nuclear collisions and how the information derived from such collisions can improve the understanding of nuclei, nuclear matter and neutron stars. Surprising as it may seem at first, constraints on the pressures that support a neutron star can be obtained by probing the pressures that are achieved in nuclear collisions or by examining the nuclear forces that bind very neutron-rich nuclei. Such nuclear properties can be related to neutron star properties through their common dependence on the equation of state of nuclear matter, which plays the same role for nuclear systems as the ideal gas law plays for gases. Finding appropriate constraints on the nuclear equation of state requires the development of new experimental devices, new experimental measurements and theoretical developments.

One of the largest uncertainties in the nuclear equation of state concerns the symmetry energy, which describes how the energy of nuclei and nuclear matter changes as one replaces protons in a system with neutrons, making the system more and more neutron rich. In some regions in the interiors of neutron stars, matter can be of the order of 95% neutrons. Whether this matter collapses under the gravitational attraction of the neutron star depends on the repulsive pressure from the symmetry energy. Experimental measurements presently do not satisfactorily constrain the pressure from the symmetry energy. Some of our recent experiments have provided constraints on the symmetry pressure; one of our goals is to make such constraints more stringent.


Recently, our group commissioned the new High Resolution Array (HiRA), shown in figure, and applied this new device to investigations of the symmetry energy. This device was constructed by a collaboration of scientists at NSCL, at the University of Washington in St. Louis and at Indiana University. It was recently used to measure the correlations between protons emitted in the collision; such correlations can be inverted to obtain an image of the expansion of a compressed nuclear system and thereby determine the expansion rate. Members of our research group, some of whom are shown in the picture, played important roles in the development of HiRA, as they do with our other research instruments. Students also play important roles in the interpretation and theoretical modeling of the data that they measure, providing them with opportunities to also probe theoretical aspects of the phenomena that they are investigating.