Microdensitometer readings

Figure 3. Example of a radial scan. The microdensitometer readings Ds are plotted against a radial coordinate. The signal-to-noise ratio is poor because of...

One of the great advantages of the fixed-film fixed-crystal technique is that even with a conventional x-ray tube, it makes possible the observation of extremely weak diffuse lines or satellites. It is thus an outstanding tool for the study of low-dimensional conductors, but some experience is required to read the patterns. To improve the accuracy of the measurements (e.g., extraction of accurate wave vector coordinates) a microdensitometer reading is often necessary (see, e.g., Ref. 119). Film results can also be used as a starting point for counter measurements (see, e.g., Ref. 74). 

The standard deviation of each scanner reading has been estimated to be 0. 7 when using a scale of 0-255 units, and the positional accuracy of the instrument is claimed to be 2pm. Data from the microdensitometer are stored in binary format on magnetic tape as an array, typical dimensions being 600 x 600. Prior to analysis the data are reconverted to integer format and copied into a random-access disc file. 

Figure 2. Calibration curve for the Daresbury Optronics P-1000 microdensitometer by using Ilford Industrial G x-ray film. The figures above the data points indicate the nominal optical density of each measurement, assuming that a scanner reading of 255 corresponds to three optical density units.

Tntium-sensitive Ultrofilm (LKB Industries, Rockville, MD) IS exposed by placing the slides side-by-side against the film in an X-ray film cassette and the entire sheet is exposed at 4°C. After exposure, the film is developed for 5 min at 20°C in Kodak D19 developer, rinsed in a stop bath, and fixed in Kodak Rapid Fix for 5 min at 20°C. The film is rinsed in running water for 20 min at 20°C, rinsed in Photo-Flo solution, and hung to dry. Optical densities of these autoradiograms can be read by a variety of microdensitometers. 

---