Evidence for shape polarization from the emission of complex fragments by compound nuclei

The degree of shape polarization occurring in the decay of the CN as a function of the exit channel depends not only on the atomic number of the emitted fragment but also on the temperature of the compound nucleus. To determine whether this shape evolution occurs at other bombarding energies and to investigate its temperature dependence, silver targets were bombarded with 40-130 MeV 3He beams. Energy spectra for He to Ne decay products observed at different bombarding energies are shown. A striking feature of this figure is the difference in shape observed for the light and heavy decay products He and O, respectively: the He spectra show the typical Maxwellian shape and the O spectra show a Gaussian shape reminiscent of fission. At all bombarding energies, the spectra show an evolution from a Maxwellian to a symmetric shape as the fragment's atomic number increases from He to 0