50 



BIOPHYSICALLY ACTIVE X-RAYS 



The color of the fluorescence is greatly dependent upon the wavelength 

 of the x-radiation. If too short a wavelength is used, practically no 

 fluorescence occurs. 



6600 



4000 

 Violet 



l 5000 j j 6000 



Blue Green Yellow 



7000 A 



Fig. 1-21. These curves show the relative spectral distribution of the emissions 

 from a commercial form of fluoroscopic screen with its maximum in the region of 



o 



most sensitive cone vision. Wavelength 5560 A; color yellow-green. The calcium 

 tungstate screen with its blue emission is used for photographic roentgenological 

 examination of body structures. Note the position of its emission spectrum in 

 relation to the curve for sensitivity of high-speed x-ray photographic film. 



Each type of luminescent compound emits a definite spectral range 

 of fluorescent radiation with one or more spectral bands possessing 

 maxima of rather definite wavelengths. The more common forms of 

 salts that are used in the construction of fluoroscope screens are shown 

 in Table 1-9. 



The relative position of the fluorescent bands emitted by a commercial 

 fluoroscopic and roentgenographic screen and their relative visibility 

 as compared with the photographic spectral sensitivity of a high-speed 

 x-ray film are shown in Fig. 1-21. From these curves it becomes appar- 

 ent that a fluorescent screen with an emission maximum in the yellow 

 green is eminently well adapted for radioscopic work, and that calcium 

 tungstate with its blue fluorescence is best adapted for photographic 

 work. 



Application of Fluorescent Screens to Radiology 



If the luminescent material is applied in a thin layer to a cardboard 

 screen support, and if the mounted compounds emit visible radiations 

 when excited by x-rays, we have a technical radioscopic screen. These 



