SMALL-ANGLE NEUTRON-SCATTERING FROM NANODROPLET AEROSOLS

We report the first measurements of small angle neutron scattering fro m an aerosol. The aerosol was produced by expanding a D2O-N-2 vapor mi xture in a supersonic Laval nozzle. The neutron wavelength (0.5 nm) is less than the typical particle size, and we can therefore derive the average particle size (5-8 nm), number density (similar to 10(12) cm(- 3)), and polydispersity of the size distribution directly from the exp erimental data rather than by inferring them from complex models of pa rticle formation and growth. We also predict and observe a Doppler shi ft-induced anisotropy in the scattering pattern due to the directed mo tion of the aerosol in the nozzle. Further applications of this new te chnique are discussed.