This RIA award will investigate the effect of microstructural variations on the radiative shielding capability of microspheres filled with composite materials. Observed changes in shielding efficiency are to be related to the mechanisms active for wave front or particle interference of the microstructure under consideration. Based on these results and theoretical arguments, models of microstructure dependent behavior will be developed. These models will then be used to predict enhanced shielding for radiation of different types and for particles of varying energy.