The fluorescent material of the enhanced screen can emit visible fluorescence by X-ray irradiation, and it may continue for a short period of time after the X-ray is stopped, which is called afterglow phenomenon. If the film is loaded in the afterglow time, the film can be repeated photosensitive, that is, in the picture of the last image residue. With increasing the use of the screen and aging, afterglow time will be extended. In accordance with the "X-ray screening screen afterglow test and its significance" in the discussion, the ordinary calcium tungstate screen should be after a single irradiation after the more than the above; the rare-earth increase screen after a single irradiation static $number s above, you can open the second film. This not only to avoid the impact of afterglow on the latter piece of film, but also to make the previous film sensitive enough, especially without a cassette automatic film-changing photography system, should be appropriate to adjust the automatic film gap time, to eliminate the image interference.