Slow neutron scattering with small angle. 5-6

The principle, experimental apparatus, and applications of small angle neutron scattering are briefly reviewed. As for the principle, the mathematical expressions for the nuclear and magnetic scattering cross sections of neutrons are given. The advantages of utilizing cold neutrons are also discussed. As for the experimental apparatus, the one at ILL, Grenoble, is introduced with a bird-eye view, a schematic diagram, and the fundamental parameters of the apparatus. The calculated and measured spectra of neutron flux at the exit of a guide tube are also presented. The first example of the small angle neutron scattering is the measurement of void distribution within aluminum single-crystals irradiated with fast neutrons, which was carried out at Juelich. The second problem is the magnetic unevenness in the single crystal of Fe-Ni invar alloy. The third application is the observation of the helical structure of the tobacco mosaic virus in D2O. It is suggested that significant informations are expected to be obtained about the conformation of RNA in virus from the results of this observation. (Aoki, K.)