212 



RADIATION BIOLOGY 



ENTRANCE 

 SLIT 



(*) 



REFLECTING 30" 

 PRISM OR GRATING 



CONCAVE 

 MIRROR 



ft--™— 



DOUBLE" 

 SLIT 



(c) 



CONDENSER 

 MIRROR 



SOURCE 



ENTRANCE 

 MIRROR 

 BEFORE 

 LOWER SLIT 



ENTRANCE 

 SLIT 



CONCAVE 

 MIRROR 



\ 



PLANE 

 GRATING 



ELLIPSOIDAL 

 FOCAL CURVE 



\ 



/ 

 / 



EXIT 

 SLIT 



Fig. 3-24. Single-monochromator optical systems frequently used for the ultraviolet 

 and visible. Mounting a employs a single prism or several prisms in tandem. Con- 

 cave spherical or parabolic mirrors may be used in place of lenses to eliminate focusing 

 adjustments for wave length. Mounting b is the Thollon biprism arrangement often 

 used in the ultraviolet and visible with crystal quartz prisms. Mounting c is the Litt- 

 row arrangement used in some commercial spectrophotometers. The dispersing 

 element may be a 30° reflecting prism or a reflection plane grating. The d mounting 

 involves a converging beam incident to the dispersing element. Either prisms or 

 reflecting plane gratings may be used. This arrangement is especially useful for 

 producing a magnified spectrum. 



