A four-circle diffractometer on a focused, tuneable synchrotron radiation source: mechanical design, computer control and evaluation of system performance

Abstract

An Enraf-Nonius CAD-4 diffractometer has been specially adapted and mounted on a computerautomated alignment carriage for use with the synchrotron radiation X-ray source at SSRL. A separatedfunction focusing monochromator system is used [Hastings, Kincaid & Eisenberger (1978). Nucl. Instrum. Methods, 152,[167][168][169][170][171] to provide radiation which is rapidly tuneable from 3-9 keV. Software for automatic alignment of the goniometer for wavelength calibration and for monitoring the decay of the stored beam have been developed. Integrated reflection intensities were 40 times higher than for the same reflections recorded using a fine-focus X-ray tube (Nifiltered Cu Ke, 40 keV, 30 mA), for SPEAR conditions of 3.7 GeV and 20 mA with colliding beams. For crystals of low mosaic spread, the reflection widths were around 0.015 °. For such narrow reflections, intcgratcd intensities can be measured to 2.7Y/o accuracy. For wider reflections, 2.1~ accuracy has been obtained. A comparison of data collected with synchrotron radiation and a sealed-tube source gave an R factor based on F of 1.8Yo. Thus, accurate structure factors are easily obtained from the synchrotron radiation data. The use of a highly mosaic monochromator crystal resulted in intensity gains at the expense of wider scan widths. The apparatus makes possible anomalous scattering experiments close to absorption edges, rapid data collection from weakly diffracting samples and possible increases in signal-to-noise ratios from samples of low mosaicity.

L3-edge anomalous scattering by gadolinium and samarium measured at high resolution with synchrotron radiation

“…The modified Enraf-Nonius CAD-4 diffractometer described by Phillips, Cerino & Hodgson (1979) was used on the SSRL Beam Line 1-5, where a channel-cut silicon crystal selects the wavelength. The radiation is reflected by the (220) plane on __ one side of the channel and then by the (220) plane on the other side, resulting in an exit beam traveling in the same direction as the incident beam, but displaced vertically.…”

Anomalous scattering of X-rays by cesium and cobalt measured with synchrotron radiation

“…Measurements were carried out with the SSRL diffractometer system which includes a doubly curved mirror and a two-crystal germanium (111) monochromator to focus the beam and select the wavelength (Hastings, Kincaid & Eisenberger, 1978), an Enraf-Nonius CAD4 diffractometer with scintillation counter to measure diffraction intensities, an ionization chamber to monitor the incident beam intensity, and a PDP 11/34 computer to record the data and to control the operation and mechanical adjustments of the equipment. A detailed description of the system and its performance has been given by Phillips, Cerino & Hodgson (1979). The diffractometer is enclosed in a steel box ('hutch') for radiation safety.…”

Atom distributions in sigma phases. I. Fe and Cr atom distributions in a binary sigma phase equilibrated at 1063, 1013 and 923 K

“…General considerations for such experiments have been set forth by Phillips, Cerino & Hodgson (1979) and by Yakel (1980). Particular conditions for this experiment included: 2.06-2.07 GeV (1 eV = 1.6 x 10 -19 J) stored electron energy; flat Ge (1 1 1) crystals in (1,-1) geometry monochromating the photon beam from a focusing mirror set for a 10 keV cut-off; an N2-filled ionization chamber measured the incident-beam intensity.…”