Topics in..
.
Edited by GALEN W. W I N G , Seton HoII University, So. Orange,
N. J. 07079
These articles, most of whieh are to be contributed by guest by calling attention authors, are intended to serve the readers of this JOURNAL lo new developments i n the t h w , design, or availability of chemical laboratoy insbumentation, or by presenting useful insights and explanations of lopies that are of praekkal importance lo hose who use, or teach the use of, modem instrumentation and instmmental techniques.
XXXIII. X-Ray Diffraction Analysis
(continued)*
Part Three-Detectors1 Reuben Rudman, Department of Chemistry Brookhaven National Laboratory, Upton, N.Y. 11973
Three methods are commonly used t o detect X-rays: fluorescent screens, film, and counters.
Fluorescent Screens Materials which emit visible light when placed in an X-ray beam have been coated on cardboard or plastic to form fluorescent screens. Zinc cadmium sulfide and calcium tunwtate are two phosphors which have been widely used. The screens usually have a protective screen coating over the fluorescent material that provides resistance to abrasion, chipping, and peeling (Fig. 33). Fluorescent screens are used for two purposes: (a) To locate the primary beam d e n adjusting apparatus. The screen should be placed a t the end of a long rod so that the operator's hands need not be exposed to the direct beam. ( b ) To decrease the required exposure times when film is used as the detector. I n this ease the screen is placed in contact with the film so that the film is exposed to the light emitted by the screen as well as to the diffracted X-rays. Examples of commercially available screens are Radelin X-ray screens (various types of intensifying (medical and industrial) and fluoroscopic screens) produced by the U.S. Radium Corp. and the DuPont
Cronex Xtra Life Intensifying Screens (PAR speed a t $6.75 a pair and H I speed at $7.40 apair).
Film X-rays affect photographic film in much the same way %as does visible light. However, the emulsion on ordinary film is too thin to absorb much of the incident X-radiation. For this reason, X-ray f i l m are made with rather thick layers of emulsion and large grain siee. Film techniques are used for recording both the positions and intensities of the reflections. If meaningful intensity measurements are to be made, special care must be taken in the handling and developing of film. The proper technique has been discussed elsewhere (Ref. ( 6 ) , pp. 78-111; Ref, (If), pp. 364-76). Morimoto and Uyeda (13) reported the results of tests on 43 types of commerciillly available X-ray films made bv manufacturers. These films " eizhteen .. wrrr trttrd for. filr!! S I R C ~ . f
