Number 194 (Story #1), September 13, 1994 by Phillip F. Schewe and Ben Stein CRITICAL EXPONENTS IN NUCLEAR PHYSICS: In the 1970s physicists found that a variety of physical systems exhibited a universal behavior near a certain critical point. Examples include ferromagnets near their Curie temperature (below which atomic magnetic moments line up) or fluids near to those conditions of temperature and pressure where the gaseous and liquid phases coexist. These systems were observed to be characterized by "critical exponents" which typified the exponential temperature dependence of the system (e.g., the magnet's susceptibility or the fluid's density) near the critical point. Scientists at the LBL Bevalac have now demonstrated that the fragmentation of a gold nucleus (accelerated up to energies of 1 GeV per nucleon) upon striking a carbon target acts like a critical system. They detected the collision debris and catalogued events according to the size and multiplicity of the fragments. Using the multiplicity as the equivalent of "temperature," the nuclear physicists were able to plot various fragment distributions and to extract the same sort of critical exponents studied by condensed matter physicists. The calculated values are very close to those which characterize liquid-gas systems. (M.L. Gilkes et al., Physical Review Letters, 19 Sept. 1994.)