A simple automatic cassette for X‐ray synchrotron topography

Use of synchrotron radiation for X-ray topography has led to an enormous reduction in exposure times and the possibil ity of rapid step by step experiments to study such phenomena as dislocation dynamics or magnetic domain wall motion. The rapidly expanding field has been reviewed recently by Tanner (1977). However, even though the exposure time may be as little as a few seconds (and with the advent of X-rays from storage rings this will be reduced even further), the time required to change manually the X-ray plate, clear the experimental area of personnel and open the shutter is typically two minutes. In short, experiments are severely limited if plate changing is not automated. To promote rapid insertion and withdrawal of the Ilford L4 25 #m nuclear emulsion plates into and out of the diffracted beam a slide projector has been used in reverse as follows. The focusing lens was removed and a hollow brass cylinder was inserted in its place to eliminate X-ray damage to the plastic casing. Each X-ray plate (2 x 2") was mounted in an aluminium frame and placed consecutively in one of the 80 slide slots of a horizontally mounted circular slide magazine. The aluminium frame was necessary to prevent the thin plates from jamming. The loaded projector was then encased in a light-tight black plastic bag and positioned in the experimental area so that an X-ray plate would receive a particular X-ray reflexion when moved into the normal slide projection position. The quartz halogen projection lamp was removed and a lead screen was placed in front of the projector to cover all but the brass tube to avoid fogging of the stacked plates. The experiment could then be completely automated and controlled remotely from outside the experimental area. Multiple exposures were affected simply by advancing the slide magazine by one. The latter operation took approximately 11⁄2 s, meaning that the exposure time and the plate changing time were of the same order of magnitude. Also, the overall experimental time was greatly reduced as in, for example, a study of magnetic domain wall motion while the magnetic field was increased stepwise. 22 plates were exposed in 15 min, whereas under normal conditions this would have taken approximately 90 min. In this experiment, the time limitation was in the exposure time for the plate. Because of chemical reaction between the aluminium, nuclear emulsion and developer the plates needed to be removed from the frames prior to development. In future, plastic frames will be used, and the plates developed in their frames.