A sagittal focusing and scanning monochromator for 8–80 keV synchrotron radiation at DORIS III

Abstract

A compact incident beam monitor for use with protein crystallography has been developed at Argonne's Structural Biology Center at the National Synchrotron Light Source (beamline X8C). Monitoring the incident x-ray beam at a synchrotron source is eli tical if accurate normalization factors are to be recorded. and a beam monitor must be capable of operating through a wide dynamic range. In the present design, incident beam intensity is monitored by measuring radiation scattered from a thin polymer film into a PIN diode. The response of the diode is linear over a range of 10 orders of magnitude. For improved statistical accuracy, the scat--tering film can be replaced with a thin metal foil. Results from measurements with Cr. Mn, Fe and Co foils indicate that fluorescent radiation emitted by a metal foil can increase the beam monitoring signal up to 50 times that produced from scattering alone. With this detector design, the direction of the forward scattered radiation is restricted to an area not larger than the beam stop, minimizing excessive background radiation in diffraction measurements. Suppm1 materials have been optimized so that no unwanted absorption edge effects are present between 6-19.5 ke V. This design makes the detector useful for monitoring incident beam intensities over a wide range of absorption edges often associated with multi wavelength anomalous diffraction (MAD) expeliments. Accurate incident beam monitoring also simplifies optimization of the x-ray beam through the diffractometer collimation after each new electron orbit of the synchrotron is established. This device would be particularly well-suited for operations on third-generation synchrotron source beamlines. An induction furnace has been constructed to provide a temperature range of 290-2500 K and a cryogenic chamber using a closed-cycled refrigerator has been assembled to cool powder samples from room temperature down to 20 K. The furnace and cryostat are designed as parts of an integrated program to enhance the powder diffraction facilities at the SRS, Dares bury Laboratory. In this work we describe the commissioning of these devices for high resolution powder diffractometry. Powder diffraction results from standard tungsten and silver samples are presented to demonstrate the operation of the apparatus and some of the early experimental results are included. The first KOSSEL experiments using synchrotron radiation were pe1formed in 1992. The exposure time was drastically reduced due to the high intensity of polychromatic synchrotron radiation at HASYLAB. When using imaging plates, serveral seconds of exposure times are sufficient. When using X-ray films, the required time increases to the few minutes. KOSSEL patterns of crisp contrast could be obtained from elements, alloys, intermetallics, semiconductor compounds and minerals.The following problems received special attention: PS01.02.19 KOSSEL-TECHNIQUE BY MEANS OF SYN-CHROTRON BEAM EXCITATION-•Proof of minor tetragonal distortions (c/a :e: 1,02) in FeAl cylindrical specimen, as a f...