A stopped-flow apparatus is described for X-ray scattering and X-ray absorption studies. It can be successfully operated over a wide temperature range down to 253 K with highly viscous solutions (20 cP). The characteristics of the stopped-flow apparatus and its application to studies of biological reactions are reviewed.

&Se and PbSeCd films, g o w n by two different nonequilibrium growth Whniques. laser-assisted deposition and elecbon-beam evaporation, on two differed types of subsuate, KCI and BaFz. are investigated. The crystal structure of the films is studied by x-ray and reflecting high-energy electron diffraction. On the basis of the structural investigations it is found thal lhe films grown by both non-equilibrium techniques represent heterophase junctions beiween the metastable WI-type phase and ule stable FCC phase. The growth mechanism is semiquantitafively discussed in the framework of Sirota's examinations of the formation of the metastable phases. 'Ihe substrate type is found to intluence only the metastable-phase lanice mnstanL which in lum determines the lhickness of the metastable-phase sublayer.

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Human immunoglobulin (IgG), bovine fibrinogen and bovine serum albumin were irradiated at room temperature with short pulses (50 ns to 2 μs) of 16 MeV electrons in 0.2 M NaClO4 solution containing phosphate buffer (pH 7.5). In the presence of N2O the intensity of light (LSI) scattered by the protein solutions increased after the pulse indicating aggregation. The latter process originates from the attack of protein molecules by OH radicals (aggregation is impeded by t-butanol and augmented by N2O). Upon plotting the relative increase of LSI vs. log time (after the pulse) sigmoidally shaped curves were obtained. From these findings and results of optical absorption measurements the following is inferred: Aggregation occurs as a consequence of chemical alterations of the protein molecules induced by the attack by OH radicals. The transient species formed during and a few pis after the pulse are reacting within a period of several ms. At the end of this period the formation of aggregates starts. It is concluded that the primary radiation chemical process consists (among others) in the generation of nuclcation sites. The latter subsequently initiate aggregation processes.