144 RADIATION moLOGY 



Tabke 4-2. Ui/rRAVioLET Filters. — (Continued) 

 l-oiiH-wavc |>ass Reference 



280-300 Bass, 1948; Itowcn, lltKi; Maclean el al., 



1045 



280-:i20 Corning, 1U18; Scliult-.lena, 1952 



290-310 Polaroid, 1951 



300-310 Kasha, 1948; Ley ami Wingdien, 1934; 



Saiiiidcrs, 1928 



300-330 Corning, 1948; 8chott-Jena, 1952 



310-330 Kasha, 1948; Polaroid, 1951; Schott-Jena, 



1952 



315-365 Maclean et al, 1945; Schott-.Iena, 1952 



340-300 Kaslui, 1948; Schott-Jena, li)52 



340-380 Corning, 1948; Schott-Jena, 1952 



;^50-380 Polaroid, 1951 



360-400 Bowen, 1946; Corning, 1948; Schott-Jena, 



1952 



365-430 Corning, 1948; Schott-Jena, 1952 



380-410 Eisenlirand and von Hallian, 1930; Pola- 



roid, 1951 



420 Bowen, 1946 



more or less strongly, all wave lengths other than those of the selected 

 region. Such filters are simple to use, may be made in large dimensions, 

 and place no limitations on the angular spread of the radiation to be 

 transmitted. On the other hand, it is difficult to obtain absorption filters 

 which can provide both a narrow transmission band and high transmis- 

 sion within the band; further the design of an absorption filter for any 

 particular spectral region is a wholly empirical enterprise. 



Absorption filters may be made of glass, of liquid cells, or of gas-filled 

 cells (chlorine and bromine) or combinations of these. In general, a 

 filter need not (and will not) transmit only a narrow band of wave lengths 

 out of the entire electromagnetic spectrum. Consideration must be given 

 to the characteristics of the radiation source and the radiation detector, 

 or biological subject, to be employed. Transmission bands in far-removed 

 wave-length regions, such as the infrared, might well be of no consequence 

 in particular investigations. 



References to band-pass and long-wave-length-pass absorption filters 

 for various regions of the ultra\'iolet are summarized in Table 4-2. 

 Appropriate combinations of these may be employed for isolation of par- 

 ticular spectral lines from various sources. 



If the absorption of the ultraviolet radiation involves a photochemical 

 decomposition of some component of the filter, the filter may have to be 

 renewed frequently. This is particularly likely with liciuid filters includ- 

 ing organic components. Such decompo.sition may sometimes be mini- 

 mized by placing the sensitive component farthest from the source in the 

 sequence of filter elements. 



