THE COMPLEMENTARY USE OF X-RAY AND NEUTRON-DIFFRACTION IN THE STUDY OF CRYSTALS

Neutrons and X-rays interact differently with atoms in crystals. While X-rays primarily give information on electron distributions, neutrons report on nuclear positions, and, through the spin interaction, are s ensitive to magnetic structure. These and other differences have been exploited for many years in, for example, X-N difference studies and i n determining magnetic structure. The major differences in available X -ray and neutron incident-beam intensities have also influenced the wa ys in which the two probes are exploited; not only are neutron sources inherently weaker, but this disadvantage is heightened by the weaker neutron-nucleus interaction. Advances in sources of both types, couple d with developments in instrumentation, have enabled not only the rela tive strengths to be exploited more effectively, but also some of the respective weaknesses in both to be at least partially overcome. After the main relevant advantages of X-rays and neutrons, and specifically of pulsed spallation neutron sources, this paper will discuss some of the scientific areas in which these various advantages are being incr easingly exploited with advanced sources and instrumentation. Although the examples focus in particular on studies of structure and disorder in powder samples, including work at high pressures, some attention i s given to hydrogen location in, and diffuse scattering from, single c rystals. Finally, a personal forward look towards possible future deve lopments is offered.