Neutron-spectroscopy measurement of a fracton density of states

Inelastic neutron scattering, combined with Brillouin and elastic small-angle neutron scattering, were used to test universality in the spectral dimension d. The fracton density of states, obtained here on a new fractal silica aerogel and over a large frequency interval, now gives d1.8. This suggests that d is a sensitive function of the fractal structure. © 1989 The American Physical Society.