CATHODE-RAY TUBES UvSED AS RADAR SCOPES 



103 



nent whose glow may be long persistent. 

 Both color and afterglow can be varied dur- 

 ing screen manufacture by appropriate selec- 

 tion of the phosphor components. This var- 



periment. Because it is only rarely possible 

 to predict the luminescent properties of pro- 

 posed new phosphors, research in this field 

 must be guided by 'scientific intuition' rather 



Fig. 1. Photographs of PPI scope and single pip 

 The photograph shows the PPI scope actuall.y used in several experiments at The Johns Hopkins 

 University. It is a 7BP7 tube, made by RCA; it has an effective diameter of 6 inches. The radial line 

 is the rotary siveep; the concentric lines are electronic reference rings used in estimating range. The pip 

 in these pictures is seen at slightly more than 10 miles, counting each ring as 5 miles. Pip sizes shown 

 are (a) 1^8x1°, (b) 1^8x60°, (c) 30ms x 1°, and (d)30Atsx 60°. 



iation is largely empirical; rationalization of 

 phosphoric luminescence in terms of atomic 

 weights or any other scheme has defied ac- 

 complishment. Leverenz of RCA states, for 

 example, "There are, as yet, no theories 

 which give quantitative agreement with ex- 



than logic" (29). In cooking up a batch of 

 phosphor the manufactm*er pays attention to 

 crystal size, valence, impurities and other 

 factors; and in coating the glass tube, the 

 thickness of the coating, degree of optical 

 contact, and even thickness of the glass must 



