FACILITIES

ROTATING

X-RAY ANODE DIFFRACTION UNIT

Stationary anode X-ray tubes have been used for most conventional X-ray diffraction generators. However, since a large amount of heat energy is generated by the electron beam bombardment on the anode, the X-ray intensity is limited. The rotating anode tube can give higher intensity X-rays because the water-cooled anode is rotated at a high speed to distribute the heat energy over the circumferential surface of the anode.

Capability: The maximum operating conditions for this unit are 60 kV and 100 mA. This produces X-rays whose brilliance is 10 to 20 times greater than that of the normal sealed X-ray tubes. This makes it possible to reduce the exposure time dramatically in the photographic method, to scan rapidly with a counter, or to study dynamic changes or transformations in the crystal structure.

Applications: Measurement of the long period in chain-folded polymer crystals. Crystallographic studies of paraffins; observations of phase changes in polymer and paraffin crystals; X-ray diffraction patterns from wet collagen; detection of small amounts of crystalline impurities.

Availability: The use of this instrument by NBS research workers on problems of mutual interest can be arranged. It must be operated only under the direct supervision of the scientist in charge of the instrument.

Contact: Dr. Darrell H. Reneker, Chief, Polymer Crystal Physics Section, Polymer Building, Room A209, Phone 301-921-3344.

oplications: Chemical analysis for the light elements own to lithium in atomic number (except oxygen id nitrogen with the spectrometer as presently set); is application would be particularly useful when sociated with surface and shallow skin depth pheOmena, such as the identification of boride, carbide, nd sulfide precipitates on a fracture surface, for exmple. Application to other types of metallurgical henomena such as detection of dezincification in rass and the reduction of iron oxide in the aluminizng of steel sheet; in the case of the higher atomic umber elements, transitions between outer electron evels, and transitions from the valence band to outer evels are observed. Valence band spectra as a funcon of the state of chemical combination; the bulk of the work that has been done on this instrument has een the study of valence band structure to obtain a etter understanding of the principles of intermetallic ompound formation and the electronic basis for heir physical properties.

Availability: To any qualified NBS research worker.

Also, in appropriate situations the facility can be nade available to researchers from other government, education and industrial organizations.

materials scientists concerned with bonding, electronic configurations, lattice and atomic vibrations, coordination, valence states, and other properties.

Availability: On a selective basis when not required for Crystallography Section programs. The instrument must be operated by Section personnel and only work of mutual interest can be undertaken. Literature:

[1] Inorganic Chemistry, 9, 2228 (1970).

[2] Crystal Structure Communications, 1, 247 (1972).

Contact: Dr. Alan D. Mighell, Room B222, Materials Building, Phone 301-921-2950.

THREE-CIRCLE

X-RAY DIFFRACTOMETER

Operating completely under computer control, the instrument orients a single crystal in the x-ray beam and records the diffracted intensity for each of several thousand reflections.

Capability: Data are collected at rates up to 1000 reflections per day. Accuracy is indicated by the final R value obtained after least squares refinement. Typical values are in the range 3 to 5%.

Applications: Structural parameters, including bond lengths, angles between bonds, and amplitudes of thermal vibrations are obtained. Precise three-dimensional diagrams can be drawn to scale. Diagrams of this type are used by physicists, chemists and other

THREE CIRCLE X-RAY DIFFRACTOMETER. Diagram of the cobalt imidizole complex cation in the compound Co (Im,) (NO). The ellipsoids represent the root-mean-square amplitude of thermal oscillations of atoms.