190 



RADIATION BIOLOGY 



for mirrors and for producing diffuse reflection and scattering inside cham- 

 bers; and (3) highly absorbing material such as low-reflectance black 

 coatings and metallic blacks. 



TRANSPARENT MATERIALS 



The optical properties of the important transparent materials for prisms 

 and lenses are available in several monographs on spectroscopy (Harrison 

 et at., 1948; Sawyer, 1944) and physical methods (Strong, 1943) and in 

 the various physical and chemical handbooks. The optical properties of 



200 



250 



300 



350 



3000 



4000 



5000 



400 1000 2000 

 WAVE LENGTH, m^ 



Fig. 3-16. Spectral transmission of various types of transparent materials. 



halide crystals, useful in infrared spectroscopy, have been summarized 

 by the Harshaw Chemical Company. 



The most useful window materials are fused quartz (sihca), the glasses, 

 and some of the transparent plastics. Their transmittances are plotted 

 in Fig. 3-16. The transparent plastics, especially the acryhc (Lucite and 

 Plexiglas) and polystyrene, are relatively inert chemically, fairly resistant 

 to continuous exposure to water, and transparent in the ultraviolet to 

 about 300 m/i (Kremers, 1947; Wearmouth, 1943) (Fig. 3-16) and in the 

 infrared to about 2200 m/i. Silver chloride, when grown as a synthetic 

 single crystal, has the mechanical properties of a tough plastic and can 

 be rolled into thin transparent films and pressed into optical components 

 such as lenses (Harshaw Chemical Company; Kremers, 1947). When 

 freshly prepared, it is very transparent, but its visible transmittance 

 decreases rapidly on exposure to the visible and ultraviolet. It is especi- 

 ally useful as a window material for the infrared from 1 to 25 ^l. Since it 

 wets glass and metals at 200°C, infrared absorption cells and windows 



